Discoveries

Efflux pumps constitute 21% of AMR in human gut species but only 1% in aquatic (η²=0.127). Metal resistance constitutes 45% in soil/aquatic but 6% in human gut (η²=0.107). Clinical species have 68% accessory (acquired) AMR vs soil 43%. Within 823 multi-environment species, clinical strain fraction predicts total AMR (rho=0.465, p=2.2e-45). K. pneumoniae has 1,115 AMR clusters (only 7 core) across 13,637 genomes. All findings survive family-level phylogenetic control (20/141 families significant). This is the largest genomic AMR-environment analysis to date, extending Gibson et al. (2015, 6K genomes) by 50×.

Cofitness analysis of 801 AMR genes across 28 organisms reveals that AMR cofitness neighborhoods are enriched for flagellar motility (GO:0071973, 5 organisms FDR<0.05), flagellum assembly (GO:0044780, 5 orgs), histidine biosynthesis (GO:0000105, 3 orgs), and tryptophan biosynthesis (GO:0000162, 3 orgs). This enrichment is undetectable with old FB SEED annotations (0/280 significant) — only InterProScan GO (68% coverage) reveals it. Support networks are organism-specific (cross-mechanism Jaccard 0.375 >> within-mechanism 0.207, MWU p=4.3e-13). AMR genes are in larger-than-average ICA modules (median 46 vs 27, p=1.7e-8). The co-regulation with motility and biosynthesis suggests AMR costs reflect competition for the proton motive force.

Random-effects meta-analysis of 801 AMR genes across 25 organisms shows a pooled fitness shift of +0.086 [+0.074, +0.098] when AMR genes are knocked out — all 25/25 organisms positive. This cost is mechanism-independent (KW p=0.89), conservation-independent (core = accessory, p=0.33), and tier-independent (bakta_amr = keyword, p=0.26). The uniformity suggests compensatory evolution has equalized costs to an irreducible floor. However, mechanism strongly predicts conservation status (metal resistance 44% accessory vs efflux 13%, χ²=69.3, p=1.4e-13) — acquisition history, not cost, determines whether AMR genes are core or accessory. Efflux genes (broad-spectrum) show a stronger antibiotic-dependent fitness flip than enzymatic inactivation genes (narrow-spectrum): +0.094 vs −0.001, MWU p=0.007.

Mantel tests across 1,261 species show non-core (acquired) AMR genes have stronger phylogenetic signal (median r=0.222) than core (intrinsic) genes (median r=0.117), paired t-test p=7.0e-16. This contradicts the standard model that acquired resistance is phylogenetically random via HGT. Instead, once a lineage acquires resistance elements, they are stably maintained and vertically inherited, creating clonal AMR lineages. Note: core genes have near-zero Jaccard variance by definition (>=95% prevalence), which partly suppresses their distance-based signal.

Across 1,305 species and 180,025 genomes, 51.3% of AMR gene-species occurrences are rare (<=5% prevalence), 41.3% variable (5-95%), and only 7.5% fixed (>=95%). Median pairwise Jaccard distance between strains = 0.435 — strains within the same species share less than 60% of their AMR repertoire. Atlas Core genes are 77% fixed within species; Singletons are 79% rare — validating the cross-species conservation classification at strain resolution.

1,517 resistance islands detected across 705/1,305 species, with mean phi coefficient = 0.827 (very tight co-occurrence). 88% contain multiple resistance mechanisms (efflux + enzymatic inactivation most common). Maximum island = 43 genes. These multi-mechanism islands provide coordinated defense against multiple drug classes.

Spearman rho = -0.193, p = 2.2e-12. Species with more open pangenomes have slightly lower AMR variability — unexpected. Likely because open-pangenome species accumulate more rare/singleton AMR genes below the 5% threshold, deflating the variability index (which measures the 5-95% zone).

Of 39,532 Fitness Browser dark genes with pangenome links, bakta v1.12.0 reclassifies 33,105 (83.7%). Just 6,427 are "truly dark" — both FB and bakta agree: hypothetical protein. Truly dark genes are structurally distinct: shorter (121 vs 194 aa), less conserved (43% vs 73% core), fewer orthologs (29% vs 64%), higher GC deviation (d=0.247). These properties are consistent with recent HGT outpacing annotation databases.

41% of neighbors of truly dark genes are also hypothetical, 12% are within 2 genes of mobile elements (transposases, integrases, phage proteins). This suggests dark genes concentrate in recently acquired genomic islands rather than being randomly distributed.

Contrary to expectation, truly dark genes with strong fitness phenotypes are depleted in stress conditions (OR=0.53, p<0.001) and enriched in nutrient, mixed community, and iron conditions. This suggests novel metabolic or inter-species interaction functions rather than stress responses.

Only 246/6,427 (3.8%) truly dark genes have zero annotation clues. 84.7% have database cross-references, 43.5% have eggNOG hits (though 55% of COG assignments are "S"/unknown), 29.3% have cross-organism orthologs, 9.5% are in ICA fitness modules.

Comprehensive comparison of bakta v1.12.0 vs eggNOG-mapper across 132.5M gene clusters:
- EggNOG wins on enrichment-style annotations: COG (51% vs 8.2%), KEGG (38.5% vs 17.3%), Pfam (63% vs 7.7%)
- Bakta wins on GO terms (15% vs 7.4%), product descriptions (71.2% vs 70.4%), and UniRef50 links (79.2%, unique)
- Union raises coverage from ~70% to 77.3% for "any functional annotation"
- Bakta rescues 11.2M clusters (of 39.2M) that eggNOG misses entirely

Confirmed by bakta developer Oliver Schwengers across GitHub issues #350, #385, #391, #393:
- PSC pre-computed annotations are sparse: only ~14% of PSC entries have COG, ~19% have KEGG. PSC DB is optimized for product descriptions, not functional categories.
- COG 2024 broke direct mapping: COG 2024 no longer provides representative sequences, forcing lossy indirect WP accession→IPS→PSC mapping.
- Pfam skipped by design: HMMER only runs on hypotheticals (~7.7%). The 92% with PSC matches never get Pfam searched.
- DIAMOND fast < HMM sensitivity: bakta's PSC uses DIAMOND fast mode; eggNOG uses HMM-based ortholog assignment.
- Developer planned to integrate eggNOG into PSC representatives (issue #325) — may have partially happened in DB v6.0 but limited impact.
- The Arche benchmark paper (Alonso-Reyes & Albarracin 2025, PMID 40811208) independently confirmed bakta's conservative annotation transfer vs. other tools.

• Only 33.3% of bakta's 17.6M distinct UniRef50 IDs exist in kbase_uniprot.uniprot_identifier
• The bridge reaches RefSeq (71%), OrthoDB (46%), STRING (40%), KEGG (36%) of matched IDs
• Missing from bridge: GO, EC, InterPro, Pfam — importing full UniProt would unlock these
• For now, eggNOG remains the better source for COG/KEGG/Pfam enrichment analysis

Any join that touches kbase_uniprot.uniprot_identifier can exceed spark.driver.maxResultSize (1GB) via broadcast exchange. Fix: SET spark.sql.autoBroadcastJoinThreshold = -1 to force sort-merge joins. See data/bakta_reannotation/scripts/compare_bakta_eggnog.py for the pattern.

Analysis of 172 species with sufficient data showed:
- Median partial correlation for environment effect: 0.0025
- Median partial correlation for phylogeny effect: 0.0143
- Phylogeny dominates in 60.5% of species
- Environment dominates in 39.5% of species

No significant difference between "environmental" bacteria (where lat/lon is meaningful) and host-associated bacteria (p=0.66).

Attempting to query ANI for all 13K+ genomes in a single IN clause fails/times out. Must iterate over species and query ANI for each species separately. See docs/performance.md for pattern.

The pangenome table already contains no_core, no_aux_genome, no_singleton_gene_clusters, no_gene_clusters - no need to compute from gene_cluster table.

Tested whether open pangenomes (low core fraction) show different patterns. Results:
- rho=-0.05, p=0.54 for environment effect
- rho=0.03, p=0.73 for phylogeny effect
- No significant relationship found

The 12 pangenomes without matching species clades are mostly obligate symbionts:
- Portiera aleyrodidarum (whitefly symbiont)
- Profftella armatura (psyllid symbiont)
- Various uncultivated lineages (UBA, TMED, SCGC prefixes)

These are valid pangenomes but filtered from species metadata due to single-genome status.

Analysis of 32 species across 9 phyla (357,623 genes) reveals a remarkably consistent "two-speed genome":

Novel/singleton genes consistently enriched in:
- L (Mobile elements): +10.88% enrichment, 100% consistency across species - STRONGEST SIGNAL
- V (Defense mechanisms): +2.83% enrichment, 100% consistency
- S (Unknown function): +1.64% enrichment, 69% consistency

Core genes consistently enriched in:
- J (Translation): -4.65% enrichment, 97% consistency - STRONGEST DEPLETION
- F (Nucleotide metabolism): -2.09% enrichment, 100% consistency
- H (Coenzyme metabolism): -2.06% enrichment, 97% consistency
- E (Amino acid metabolism): -1.81% enrichment, 81% consistency
- C (Energy production): -1.75% enrichment, 88% consistency

Biological implications:
- Core genes = ancient, conserved "metabolic engine" (translation, energy, biosynthesis)
- Novel genes = recent acquisitions for ecological adaptation (mobile elements, defense, niche-specific)
- Horizontal gene transfer (HGT) is the primary innovation mechanism, not vertical inheritance
- The massive L enrichment (+10.88%) suggests most genomic novelty comes from mobile elements
- Patterns hold universally across bacterial phyla, suggesting deep evolutionary constraint

Hypothesis validation: All 8 predictions from initial N. gonorrhoeae analysis confirmed across 32 species.

This represents a fundamental organizing principle of bacterial pangenome structure.

Multi-function genes with composite COG assignments (e.g., "LV" = mobile+defense, "EGP" = amino acid+carb+inorganic ion) are not annotation artifacts:

• LV (mobile+defense): +0.34% enrichment, 76% consistency
• Suggests functional modules like "mobile defense islands"
• Should not be filtered out as noise - they represent genuine multi-functional genes

Each of ADP1's 8 carbon sources requires a distinct set of respiratory chain components. Quinate requires only Complex I (all other components dispensable). Acetate requires Complex I + cytochrome bo3 + ACIAD3522 + more (the most demanding). Glucose requires no specific component (full redundancy). This is not a quantitative gradient — it's qualitatively different wiring per substrate class.

Quinate produces fewer NADH per carbon (0.57) than glucose (1.50), yet Complex I is more essential on quinate. The resolution: β-ketoadipate pathway products (succinyl-CoA + acetyl-CoA) enter the TCA cycle simultaneously, creating a concentrated NADH burst that exceeds NDH-2's reoxidation capacity. Glucose distributes NADH across Entner-Doudoroff + TCA steps where NDH-2 suffices.

Proteomics shows all three NADH dehydrogenases are expressed at similar levels under standard conditions: Complex I mean 27.6 (66th percentile), NDH-2 27.0 (59th), ACIAD3522 26.2 (48th) — all within 1.4 units of each other around the genome median (26.4). The cell doesn't switch respiratory configurations by regulating dehydrogenase expression. Instead, all three run simultaneously and the one that becomes limiting depends on the NADH flux rate from the carbon source. This is a passive, flux-based wiring system rather than an active regulatory switch.

Complex I (13 subunits, proton-pumping): quinate-essential, glucose-dispensable. NDH-2 (1 subunit, non-pumping): no growth data but predicted backup for glucose. ACIAD3522 (NADH-FMN oxidoreductase): acetate-lethal (0.013), quinate-fine (1.39). Each handles a different metabolic regime — division of labor in electron transport.

The β-ketoadipate pathway in ADP1 has 8 core genes, but 51 genes total show quinate-specific growth defects — a 7:1 support-to-pathway ratio. The support genes organize into 3 biochemically rational subsystems: Complex I (21 genes, NADH reoxidation), iron acquisition (7 genes, Fe²⁺ for ring-cleavage dioxygenase), and PQQ biosynthesis (2 genes, cofactor for quinate dehydrogenase). This quantifies a general principle: the metabolic infrastructure required to run a pathway dwarfs the pathway itself.

Of the 51 quinate-specific genes, 30 (59%) have no FBA reaction mappings — PQQ biosynthesis, iron acquisition, transcriptional regulators, and respiratory chain components are invisible to the metabolic model. For Complex I specifically, FBA predicts 1.76× higher flux on aromatics but 0% essentiality, because FBA's linear programming cannot represent the threshold effect of losing a single subunit from a multi-subunit complex.

Cross-species ortholog-transferred fitness data shows Complex I defects are largest on acetate (-1.55 vs background) and succinate (-1.39), not aromatics. ADP1's quinate-specificity likely reflects an alternative NADH dehydrogenase (NDH-2) that compensates on lower-NADH-flux substrates. The "aromatic support network" is really a "high-NADH-flux bottleneck network."

ACIAD3137 (UPF0234/YitK) and ACIAD2176 (DUF2280) correlate at r > 0.98 with Complex I genes across 8 growth conditions. Both lack FBA reaction mappings and have no assigned metabolic function. Their near-perfect co-fitness with the nuo operon suggests physical or regulatory association with Complex I.

ACIAD3522 (NADH-FMN oxidoreductase) has a growth ratio of 0.013 on acetate — essentially lethal — while showing no defect on quinate (1.39) or glucose (1.39). This is the largest condition-specific effect of any single gene in the 2,034-gene growth matrix. FBA predicts zero flux through ACIAD3522 on all conditions. Its biological role is unknown but the extreme acetate specificity suggests it catalyzes an NADH-linked reaction that is uniquely required for acetate catabolism.

After correcting NDH-2 false positives (filtering text-matched candidates to organisms with ≤2 hits per genome), the cross-species compensation test reverses: organisms WITH validated NDH-2 show LARGER Complex I aromatic deficits (mean -0.297) than those without (-0.156, p=0.52). The initial analysis (10/14 organisms with NDH-2, apparent support for compensation) was driven by misannotated Complex I subunits leaking through the text filter in 5 organisms. This demonstrates the importance of validating text-based gene identification — a finding that looked supportive was actually an annotation artifact.

31% of dispensable genes have condition-specificity scores ≥ 1.0. Top condition-specific genes for each carbon source are the enzymes biochemically predicted to be required: urease subunits for urea, protocatechuate 3,4-dioxygenase for quinate, Entner-Doudoroff enzymes for glucose, glyoxylate shunt for acetate, lactate-responsive regulator for lactate. This validates the growth matrix as a high-quality functional genomics dataset.

Hierarchical clustering of 2,034 genes by their 8-condition growth profiles produces an optimal K=3 with silhouette=0.24 — no discrete functional modules. The phenotype landscape is a gradient, with one exception: 24 genes form a tight quinate-specific module (the aromatic degradation pathway). Gene essentiality varies continuously across conditions, supporting the Guzman et al. (2018) "adaptive flexibility" framework.

Of 2,593 TnSeq-dispensable genes, 272 (10.5%) lack growth data from the deletion collection. These are systematically different: shorter (813 vs 981 bp), less annotated (91% vs 100% RAST), and less conserved in the pangenome (76.5% core vs 93.3%, p=1.4e-20). Hypothetical proteins are massively enriched (q=2.4e-25). The deletion collection has a bias toward well-characterized, conserved genes.

Robust ICA (30-50 FastICA runs + DBSCAN clustering) consistently finds 17-52 stable modules per organism across 32 bacteria. 94.2% of modules show significantly elevated within-module cofitness (Mann-Whitney U, p < 0.05; mean |r| = 0.34 vs background 0.12). Genomic adjacency enrichment averages 22.7× across organisms, confirming modules capture operon-like co-regulated gene groups.

The initial D'Agostino K² normality-based thresholding gave 100-280 genes per module — biologically meaningless. The ICA components themselves were fine; the problem was deciding which genes "belong" to each module. Switching to an absolute weight threshold (|Pearson r| ≥ 0.3 with module profile, max 50 genes) reduced modules to 5-50 genes and dramatically improved all validation metrics:
- Cofitness enrichment: 59% → 94.2%
- Within-module |r|: 0.047 → 0.34 (mean across 32 organisms)
- Modules became biologically coherent (22.7× genomic adjacency enrichment)

Caulo (198 experiments) showed the weakest signal in the pilot (2.9x correlation enrichment vs 31x for DvH), but organisms down to 104 experiments (Ponti) still produced stable modules. The key is capping components at 40% of experiments — higher ratios cause FastICA convergence failures and extreme slowness.

Several table schemas differ from the documented schema:
- keggmember uses keggOrg/keggId (not orgId/locusId) — must join through besthitkegg
- kgroupec uses ecnum (not ec)
- seedclass has orgId, locusId, type, num (not subsystem/category hierarchy)
- fitbyexp_* tables are long format (not pre-pivoted as documented)

from berdl_notebook_utils.setup_spark_session import get_spark_session works from regular Python scripts on JupyterHub — not just notebook kernels. This enables running full analysis pipelines from the command line without jupyter nbconvert. The auto-import in /configs/ipython_startup/00-notebookutils.py only affects notebook kernels.

Cross-organism module alignment using BBH ortholog fingerprints revealed 156 module families spanning 2+ organisms. The largest family spans 21 of 32 organisms across Proteobacteria, Bacteroidetes, Firmicutes, and Archaea — evidence of deeply conserved fitness regulons. 28 families span 5+ organisms.

This required using orthologs from ALL organisms in the analysis — an initial run using only 5-organism orthologs found just 27 families with no family spanning more than 4 organisms. The ortholog graph density is critical.

Using BBH pairs from 5 organisms (10K pairs, 1,861 OGs) vs all 32 organisms (1.15M pairs, 13,402 OGs) produced radically different results:
- Module families: 27 → 156 (6x)
- Families spanning 5+ orgs: 0 → 28
- Family-backed predictions: 31 (4%) → 493 (56%)

Lesson: always extract orthologs for ALL organisms in the analysis, not just a pilot subset. The ortholog graph is not additive — adding organisms creates new transitive connections.

The initial enrichment pipeline (KEGG + SEED + TIGRFam, min_annotated=3) annotated only 8.2% of modules (92/1,116). Root cause: KEGG KO groups average ~1.2 genes per term, so modules with 5-50 members almost never have 3+ genes sharing the same KO. Adding PFam domains (which have 814 terms with 2+ genes vs TIGRFam's 88) and lowering the overlap threshold to 2 increased annotation to 79.7% (890/1,116). PFam is the dominant annotation source — it provides domain-level functional labels that match module granularity.

Impact on downstream analysis:
- Predictions: 878 → 6,691 (7.6×), now covering all 32 organisms
- Annotated families: 32 → 145 out of 156 (93%)
- Three organisms (Caulo, Methanococcus_S2, Korea) went from 0 enrichments to 24-29 enriched modules

Held-out KO prediction benchmark across 32 organisms showed ortholog transfer dominates at gene-level function prediction (95.8% precision, 91.2% coverage), while Module-ICA has <1% precision at the KO level. This is expected and informative, not a failure: modules capture process-level co-regulation (validated by 94.2% cofitness enrichment and 22.7× adjacency enrichment), not specific molecular function. An ABC transporter module correctly groups binding, permease, and ATPase subunits — but each has a different KO. The right framing for module-based predictions is "involved in [biological process]" not "has function [specific KO]."

The min_annotated parameter (minimum overlapping genes to test for enrichment) must be calibrated to the annotation database's granularity. For gene-specific annotations (KEGG KOs: ~1 gene/term), min_annotated=3 eliminates nearly all tests. For domain-level annotations (PFam: many genes share domains), min_annotated=2 works well with FDR correction. Fisher's exact test handles small counts correctly — the statistical validity comes from FDR correction across all tests, not from requiring large overlaps per test.

Across 33 diverse bacteria, putative essential genes (no transposon insertions in RB-TnSeq) are 86.1% core vs 81.2% for non-essential genes (median OR=1.56, 18/33 significant after BH-FDR). The enrichment is real but modest — most genes in well-characterized bacteria are core regardless of essentiality. The signal is strongest in organisms with larger clades (more genomes = more reliable core classification).

Essential genes that map to core clusters are 41.9% enzymes and only 13.0% hypothetical — they are the well-characterized metabolic backbone (ribosomes, DNA replication, cell wall, cofactor biosynthesis). Essential-auxiliary genes (essential but not in all strains) are only 13.4% enzymes and 38.2% hypothetical. Essential-unmapped genes (strain-specific, no pangenome match) are 44.7% hypothetical — prime targets for functional discovery.

Essential-core genes are enriched in Protein Metabolism (+13.7 pp vs non-essential), Cofactors/Vitamins (+6.2 pp), Cell Wall (+3.9 pp). They are depleted in Carbohydrates (-7.9 pp), Amino Acids (-5.6 pp), Membrane Transport (-4.0 pp) — functions that are conditionally important rather than universally essential. This aligns with Rosconi et al. (2022) who found pan-genome composition influences essentiality in S. pneumoniae.

The Fitness Browser aaseqs file (fit.genomics.lbl.gov/cgi_data/aaseqs) uses RefSeq-style locus tags (e.g., ABZR86_RS) for some organisms, while the FB gene table uses the original annotation locus tags (e.g., N515DRAFT_). This caused a complete join failure for Dyella79 (0% merge rate). Only 1 of 34 organisms was affected, but any pipeline joining aaseqs-derived data with gene table data should verify locus tag consistency.

Across 194,216 protein-coding genes in 43 bacteria, there is a clear 16-percentage-point gradient from essential genes (82% core) to always-neutral genes (66% core). The same pattern holds when binning by strongest negative fitness effect (min_fit < -3 → 78% core vs min_fit near 0 → 66%) and by fitness breadth (important in 20+ conditions → 79% core vs 0 conditions → 66%). This establishes that the essentiality-conservation link from conservation_vs_fitness is not binary but quantitative.

Counter to the expectation that accessory genes impose a carrying cost, core genes are more likely to show positive fitness effects when deleted (24.4% ever beneficial vs 19.9% for auxiliary; OR=0.77 for auxiliary vs core, p=5.5e-48). Core genes participate in more pathways and trade-off situations — they help in some conditions but cost in others. This challenges the "streamlining" model where accessory genes are metabolic burdens.

Genes with strong condition-specific phenotypes (from the FB specificphenotype table) are 77.3% core vs 70.3% for genes without specific phenotypes (OR=1.78, p=1.8e-97). This contradicts the intuition that condition-specific fitness = niche-specific genes = accessory genome. Instead, core genes are more likely to have detectable condition-specific effects because they are embedded in well-characterized, essential pathways.

ICA fitness modules (co-regulated gene groups) are 86.0% core vs 81.5% baseline across 29 organisms (Fisher OR=1.46, p=1.6e-87; per-organism paired Wilcoxon p=1.0e-03, 22/29 organisms show enrichment). 59% of modules are >90% core genes. Co-regulated fitness response units are preferentially embedded in the conserved genome — the core genome is not just structurally conserved but functionally coherent at the module level.

Surprisingly, module families spanning more organisms do not have higher core fractions (Spearman rho=-0.01, p=0.914). The baseline core rate (~82%) is so high that there is no room for a gradient — families are nearly all core regardless of breadth. This is a ceiling effect, not evidence against the conservation-function relationship.

0 essential genes appear in any of the 1,116 fitness modules across 32 organisms. ICA decomposes fitness variation, so genes with no fitness data (essential = no transposon insertions) are invisible to it. This means fitness modules capture only the non-essential portion of the genome's functional architecture.

25,271 genes (17.8%) are true trade-offs — important (fit < -1) in some conditions, burdensome (fit > 1) in others. These are 1.29x more likely to be core (OR=1.29, p=1.2e-44). Core genes have more trade-offs because they participate in more pathways with condition-dependent costs and benefits. This explains why core genes are simultaneously more burdensome AND more essential than accessory genes.

The core-burden paradox is driven by specific functional categories: RNA Metabolism (+12.9pp), Motility/Chemotaxis (+7.8pp), Protein Metabolism (+6.2pp) all show core genes as more burdensome. But Cell Wall reverses: non-core cell wall genes are MORE burdensome (-14.1pp). The paradox is not a uniform property of the core genome but reflects the trade-off architecture of specific functional systems.

Genes that are both burdensome in the lab AND core in the pangenome represent the strongest evidence for purifying selection in natural environments. They're costly to maintain, yet every strain keeps them — nature requires them in conditions not captured by the lab. By contrast, 5,526 genes are costly + dispensable (candidates for ongoing gene loss), and 21,886 are neutral + dispensable (niche-specific).

Cross-organism essential gene analysis across 48 diverse bacteria (221,005 genes, 17,222 ortholog families) reveals 15 families that are essential in every organism: ribosomal proteins (rpsC, rplW, rplK, rplB, rplA, rplF, rps11, rpsJ, rpsI, rpsM), chaperonin (groEL), CTP synthase (pyrG), translation elongation factor G (fusA), valyl-tRNA synthetase (valS), and geranyltranstransferase (SelGGPS). These represent the irreducible essential core of bacterial life.

Of 17,222 ortholog families across 48 bacteria, only 859 (5.0%) are universally essential — essential in every organism where the family has members. 4,799 families (27.9%) are variably essential (essential in some organisms, non-essential in others), and 11,564 (67.1%) are never essential. Variable essentiality (the majority of essential families) demonstrates that genomic context profoundly shapes which genes an organism requires for viability.

7,084 essential genes have no orthologs in any other FB organism. Of these, 58.7% are annotated as hypothetical proteins — the least characterized yet most functionally important genes in each organism. By contrast, universally essential genes are only 8.2% hypothetical. The orphan essentials are prime candidates for novel biology.

Universally essential genes are 91.7% core vs 80.7% for non-essential genes. 71% of universally essential families are 100% core across all genomes in their species. Orphan essentials (no orthologs) are only 49.5% core — they are strain-specific essential functions that haven't been conserved across species.

By finding non-essential orthologs that participate in ICA fitness modules, we generated 1,382 function predictions for hypothetical essential genes across 48 organisms. All predictions are backed by cross-organism module family conservation. This demonstrates that module context from non-essential orthologs can illuminate the function of essential genes that are invisible to fitness-based methods.

The env_embedding_explorer project showed that human-associated samples dampen AlphaEarth geographic signal (2.0x vs 3.4x for environmental). We hypothesized this bias explained the weak environment effect in the ecotype analysis (median partial correlation 0.003). However, stratifying 213 species by dominant environment type (47% human-associated, 21% environmental) shows the opposite: human-associated species have higher partial correlations (median 0.084) than environmental species (0.051). Mann-Whitney p=0.83. The original conclusion — phylogeny dominates — holds regardless of sample environment. The geographic signal in embeddings and the environment-gene content relationship are distinct phenomena.

Using isolation_source harmonization (12 categories from 5,774 values), 106/224 species in the ecotype analysis are majority human-associated (gut + clinical). Only 47/224 (21%) are majority environmental (Soil, Marine, Freshwater, Extreme, Plant). This is a more systematic classification than the original manual species-level categorization, and confirms the clinical bias but shows it doesn't confound the ecotype results.

Environmental samples (Soil, Marine, Freshwater, Extreme, Plant) show a 3.4x ratio in embedding cosine distance between nearby (<100 km, mean=0.27) and far (>10K km, mean=0.90) genome pairs. Human-associated samples (gut, clinical) show only a 2.0x ratio (0.37 vs 0.75). Hospitals worldwide have similar satellite imagery (urban built environment), so human-associated genomes have more homogeneous embeddings regardless of geography. The pooled "All samples" curve (2.0x ratio) is dominated by the 38% human-associated fraction and substantially underestimates the true geographic signal in the embeddings.

Implication: Any analysis using AlphaEarth embeddings as environment proxies should stratify by sample type, or at minimum exclude human-associated samples. The weak environment signal found in ecotype_analysis (median partial correlation 0.0025) may be partially explained by this clinical bias.

Of 83,287 genomes with AlphaEarth embeddings, 38% are human-associated (clinical 20%, gut 16%, other 2%). Environmental categories are much smaller (soil 7%, marine 7%, freshwater 7%). This reflects NCBI's bias toward pathogen sequencing — clinical isolates have good geographic metadata from epidemiological tracking, which is why they disproportionately have embeddings.

30,469 genomes (36.6%) cluster at coordinates with >50 genomes of >10 species. However, several flagged locations are legitimate DOE/research field sites: Rifle, CO (1,883 genomes, DOE IFRC), Saanich Inlet (1,529, oceanographic time series), Siberian soda lakes (812, extremophile campaigns). The heuristic needs refinement — checking isolation_source homogeneity at each location would better distinguish field sites from institutional addresses.

3,838 of 83,287 genomes have NaN in at least one of the 64 embedding dimensions. The cause is unclear — possibly missing satellite imagery at those coordinates, or coordinates that fall outside satellite coverage (polar regions, ocean). These must be filtered before any embedding-based analysis.

In the ENIGMA contamination-functional project (108 overlap samples), primary univariate associations were non-significant across defense, stress, metabolism, and mobilome outcomes in both mapping modes. However, after adding mapped-coverage-aware sensitivity models, contamination-defense association became significant (coverage-adjusted OLS contamination p = 3.98e-4 relaxed, 3.54e-3 strict; high-coverage subset Spearman p = 0.0207 relaxed, 0.0098 strict). This indicates the strongest signal is conditional on mapping coverage/model specification rather than broad across all outcomes.

When strict and relaxed mapping modes were computed independently in NB02 (instead of reusing strict outputs), 1,140 of 1,590 genus-feature pairs differed between modes (~71.7%), and site stress scores differed for all 108 samples. Strict-vs-relaxed sensitivity is therefore analytically meaningful and should not be approximated by copied feature tables.

enigma_coral.ddt_brick0000454 currently provides taxonomy through Genus (no species/strain rows). A species-proxy mode (species_proxy_unique_genus) that keeps only unique genus->single GTDB clade mappings retained 150 genera, but mapped abundance collapsed to mean 0.031 (vs 0.343 in strict/relaxed genus modes). In this low-coverage regime, defense trend was positive (rho=0.169) but non-significant (p=0.081), indicating that true species-level gains likely require higher-resolution ENIGMA taxonomy or metagenomic mapping.

After adding explicit confirmatory vs exploratory labels in NB03 and applying global BH-FDR across all reported p-values, confirmatory defense Spearman tests in genus-level modes remained null (p=0.546/0.483; q=0.862/0.849). The strongest surviving signal was exploratory: relaxed coverage-adjusted defense model retained q=0.046, while strict and other sensitivity signals attenuated above q<0.1. Interpretation should therefore prioritize null confirmatory evidence and frame positive results as exploratory.

Re-testing confirmatory defense endpoint under four index constructions (all-metals composite, uranium-only, top-3 variance metals, PCA-PC1) did not produce significant confirmatory associations after FDR correction (all q=0.546 across 8 confirmatory-variant tests). This indicates the null confirmatory result is not an artifact of one specific contamination-index formulation.

Spearman correlation of community-weighted GapMind amino acid biosynthesis completeness against
ambient amino acid metabolomics across 131 NMDC soil samples:

• 11/13 tested aa pathways trend in BQH-predicted direction (negative r = lower community
  completeness co-occurs with higher ambient metabolite concentration); binomial sign test
  p = 0.011
• Two pathways reach FDR significance (BH-corrected q < 0.05): leucine (r = −0.390, q = 0.022,
  n = 62) and arginine (r = −0.297, q = 0.049, n = 80)
• Both FDR-significant pathways are among the most energetically expensive to synthesize (leucine:
  37 ATP equivalents; arginine: 26 ATP equivalents) — consistent with BQH predicting loss is
  most favored when the benefit of gene retention is lowest
• Methionine shows the largest effect (r = −0.496) but is underpowered (n = 18, q = 0.117)
• leu signal is robust to soil-only stratification (q = 0.022 unchanged) and to study-level
  blocking (dataset is 95% single-study; see below)
• Tyrosine is an anti-BQH outlier (r = +0.42, ns): likely explained by phenylalanine hydroxylation
  providing an alternative tyrosine source that decouples biosynthesis completeness from pool size

First demonstration that community-weighted pangenome completeness scores correlate with measured
metabolite pools at landscape scale using public multi-omics data.

PCA of 220-sample × 80-pathway GapMind completeness matrix:

• PC1 = 49.4% of variance captures near-complete Soil vs Freshwater separation (Mann-Whitney
  p < 0.0001; median PC1 Soil = +3.86, Freshwater = −6.28)
• PC1 loadings are dominated by carbon utilization pathways (glucuronate, fumarate, succinate,
  cellobiose, galactose) — not amino acid pathways
• Amino acid pathways load more strongly on PC2 (16.6%), separating sub-clusters within Soil
• 17/18 aa pathways are significantly differentiated across ecosystem types (q < 0.05 KW),
  but the primary driver is carbon substrate availability, not biosynthesis capacity

Implication: when community metabolic potential is used as a feature space, carbon substrate range
is the dominant ecological axis and will confound aa pathway analyses unless controlled for.
Use PC1-residualized or ecosystem-stratified analyses for BQH-type tests.

Study-level analysis of the 131-sample H1 dataset revealed that 95% of samples (125/131) come
from one NMDC study (nmdc:sty-11-r2h77870). The remaining 6 samples are from a second study.
This means:
- Cross-study LC-MS protocol heterogeneity is effectively absent as a confounder (contrary to
the naive expectation for NMDC metabolomics)
- The leucine BQH signal is internally consistent within one analytical protocol
- Future multi-study NMDC metabolomics analyses should count study-level sample representation
before treating the aggregate as cross-study data

Only ~2% of compounds in nmdc_arkin.metabolomics_gold have KEGG compound IDs populated.
Pathway matching must rely on compound name substring patterns rather than KEGG-based ontologies.
Key caveats:
- Substring matching introduces collision risk (e.g., 'leucine' matches inside 'isoleucine') —
use first-match-wins ordering with longer/more specific patterns before shorter ones
- Chorismate itself is rarely detected; shikimic acid and 3-dehydroshikimic acid serve as upstream
proxies but reflect precursor availability, not chorismate pool size
- Three aa pathways remain untestable (cys, his, lys) due to absent compound detections in the
175-sample overlap cohort

See also docs/pitfalls.md for the isoleucine/leucine substring collision fix.

Analysis of 1,872 bacterial species with complete pangenome, GapMind pathway, and AlphaEarth embedding data reveals:

H1: Pangenome openness → pathway completeness (r=0.107, p=3.6e-6)
- Weak but significant positive correlation
- Open pangenomes (high accessory/core ratio) have slightly more complete pathways
- Stronger relationship with pathway VARIABILITY (std dev): r=0.066, p=0.004
- Suggests accessory genes enable metabolic heterogeneity within species

H2: Niche breadth → pathway completeness (r=0.392, p=7.1e-70) — STRONGEST SIGNAL
- Moderate positive correlation using AlphaEarth embedding diversity
- Embedding variance (ecological diversity) has even stronger effect: r=0.412, p=1.8e-77
- Geographic distance alone: r=0.360, p=1.8e-58 (weaker than embedding-based metrics)
- Species with broader ecological niches require more complete metabolic toolkits

H3: Pangenome openness → niche breadth (r=0.324, p=5.6e-47)
- Moderate positive correlation
- Open pangenomes correlate with broader ecological niches
- Core fraction shows strong NEGATIVE correlation with niche breadth: r=-0.445, p=1.4e-91
- Pangenome flexibility enables adaptation to diverse environments

Key insight: AlphaEarth embedding diversity is a better predictor of metabolic completeness than geography alone. The embeddings capture ecological context (soil vs marine vs clinical), not just geographic distance. This explains why embedding variance (r=0.412) outperforms geographic range (r=0.360) in predicting pathway completeness.

Data coverage limitation: Only 6.8% of species (1,872/27,690) have sufficient AlphaEarth coverage (≥5 genomes with embeddings). This is due to missing lat/lon metadata for most NCBI genomes, especially clinical isolates.

Full pangenome analysis (27,690 species, NB11b) reveals that over half of functionally dark gene OGs are pan-bacterial, present in thousands of species across multiple phyla. Species counts range from 1 to 27,482 (median 135). This demonstrates that functional dark matter is not a minor annotation gap but a fundamental limitation in understanding broadly conserved biology. The top-ranked unknowns (COG0468, COG0443, COG0491) are present in virtually all sequenced bacterial genomes yet have zero functional evidence.

The darkness spectrum classification across 57,011 dark genes shows T1 Void (zero evidence) is only 4,273 genes (7.5%). The majority — T4 Penumbra (22,500, 39.5%) — have 3-4 converging lines of evidence (fitness phenotype, domain annotation, ortholog group, module membership). The "dark matter problem" is not monolithic: most genes have substantial clues, and the key bottleneck is targeted experimental validation, not computational inference.

Across 47 testable dark gene clusters, 29 (61.7%) show directional concordance between lab fitness condition and carrier genome environment (Fisher's combined p=0.031). NMDC independent validation confirmed all 4 pre-registered abiotic predictions (nitrogen~nitrogen, pH~pH, anaerobic~dissolved_oxygen) and all 7 pre-registered trait predictions. This provides the first systematic evidence that Fitness Browser lab phenotypes reflect real ecological function, validating fitness data as a proxy for in situ importance.

65 dark gene ortholog groups show conserved fitness effects across 3+ organisms. Dark gene concordance levels are statistically indistinguishable from annotated genes (Mann-Whitney p=0.17). Motility-related dark genes show the strongest cross-organism concordance, suggesting conserved but incompletely annotated chemotaxis machinery.

Shewanella MR-1 contributes 25/100 top fitness-active candidates, 587 scored dark genes total, and covers 20.8% of the top-500 in just 3 experiments (stress, nitrogen, carbon). This reflects deep condition coverage (121 conditions), a large dark gene complement, and high fitness effect magnitudes (142 genes with |fit| >= 4). For conservation-weighted prioritization (Route B), S. meliloti ranks first (1,630 OGs, 195 kingdom-level gaps) due to its broader coverage of conserved unknowns.

Evidence-weighted (Route A, NB09) and conservation-weighted (Route B, NB11) covering sets both select 42 organisms covering ~95% of priority, sharing 39 organisms. Route A puts MR-1 first (deep condition evidence); Route B puts S. meliloti first (most kingdom-level gaps). The complementarity enables both targeted hypothesis testing (Route A) and novel function discovery (Route B) from largely the same organism set.

Adding 25 non-FB organisms (Bacillota, Actinomycetota, Campylobacterota) to the covering set candidate pool selects 50 organisms spanning 6 phyla (vs 4 for FB-only). P. aeruginosa PAO1 ranks #1 (3,713 OGs) and M. tuberculosis reaches #6 (first Actinomycetota). However, Bacillota organisms (B. subtilis, S. aureus) are NOT selected because their kingdom-level OGs are already covered by Pseudomonadota selections. They remain valuable for studying genes in native Gram-positive context, but don't contribute unique OG coverage.

Analysis of 433 Pseudomonas species (12,732 genomes) using GapMind carbon pathway predictions reveals that the P. aeruginosa group has near-complete loss of plant-derived sugar catabolism compared to the P. fluorescens/putida group. 43 of 62 pathways differ significantly (FDR < 0.05), with the largest effects in xylose (+74 pp), ribose (+64 pp), arabinose (+63 pp), galacturonate (+60 pp), and myo-inositol (+59 pp). Amino acid catabolism remains near-universal (>99.5%) in both groups, consistent with Palmer et al. (2007) showing CF sputum is amino acid-dominated.

Among free-living species, carbon profiles are significantly associated with isolation environment (PERMANOVA p = 0.006), but predictive accuracy is modest (RF balanced accuracy 0.41 vs 0.25 chance). D-serine, arabinose, rhamnose, and fucose are the most discriminating pathways.

Four-category classification of 7 FB organisms × 23 GapMind pathways reveals:
- 35.4% Active Dependencies (complete + fitness-important)
- 41.0% Latent Capabilities (complete but fitness-neutral in rich media)
- 14.9% Incomplete but Important
- 8.7% Missing

Key insight: ALL Latent Capabilities become fitness-important under condition-specific analysis (nitrogen limitation, stress, carbon source shifts). This validates the core_gene_tradeoffs finding that lab fitness underestimates natural selection on metabolic genes.

Pan-bacterial analysis (2,810 species, ≥10 genomes each):
- Spearman(variable pathways, openness): rho=0.327, p=7.2e-71
- Partial Spearman controlling for genome count: rho=0.530, p=2.83e-203
- Signal holds across 18/21 phylogenetic groups tested
- Amino acid biosynthesis pathways (leu, val, arg, lys, thr) show largest accessory dependence gap (~0.14)

This is much stronger than the pangenome_openness project's null result for environmental/phylogenetic predictors of openness. Metabolic pathway variability is a genuine predictor.

The Fitness Browser's own KEGG tables (besthitkegg + keggmember + kgroupec) provide direct gene-to-KEGG KO-to-EC-to-pathway mapping for all 48 FB organisms. This is much simpler than the DIAMOND blastp pipeline used by conservation_vs_fitness to build a link table, and covers more organisms. The chain: besthitkegg → keggmember → kgroupec → keggconf → GapMind pathway.

Hierarchical clustering of 225 species (≥50 genomes, ≥3 variable pathways) by GapMind pathway profiles:
- Median 4 metabolic ecotypes per species, max 8
- More ecotypes correlate with pangenome openness (partial rho=0.322, p=8.0e-07)
- Top ecotyped species: Alistipes onderdonkii (8), Barnesiella intestinihominis (8)

39.8% of metal-important genes are also NaCl-important across 19 organisms and 14 metals, but this overlap reflects shared stress biology (cell envelope, ion homeostasis, DNA repair) rather than chloride counter ion contamination. The definitive evidence: zinc sulfate (0 mM Cl⁻) shows 44.6% NaCl overlap and the highest DvH profile correlation (r=0.715) — higher than most chloride-delivered metals.

After removing the ~40% of metal-important genes that overlap with NaCl stress, the core genome enrichment persists for 12 of 14 metals. Essential metals (Mo, W, Se, Hg) actually show stronger enrichment after correction (e.g., Mo delta +0.132 → +0.145). The original atlas conclusion (OR=2.08) is not an artifact.

Whole-genome fitness correlation with NaCl: Zn (r=0.72) > Mn (0.55) > Cu (0.53) > Co (0.50) > Hg (0.48) > Ni (0.45) > Al (0.42) > Mo (0.40) > U (0.35) > Se (0.34) > Cr (0.32) > W (0.30) > Fe (0.09). Metals that broadly displace cofactors share more genes with ionic stress; metals targeting specific pathways (Mo/W for molybdopterin, Fe for iron-sulfur clusters) are distinct from general stress.

Synechococcus elongatus has 12 NaCl dose-response experiments (0.5–250 mM), far more than any other organism (1–6). This makes the n_sick >= 1 threshold much easier to satisfy, producing an 88.6% shared-stress rate. Excluding SynE, overall overlap drops from 39.8% to 36.7%. Analyses using NaCl fitness data should account for experiment count when setting importance thresholds.

FW300-N2E3 produces tryptophan (WoM: Increased), has 231 genes with significant fitness when grown on tryptophan (FB), has a complete tryptophan biosynthesis pathway (GapMind), yet 0/52 P. fluorescens strains in BacDive can utilize tryptophan as a carbon source. This convergence of four independent lines of evidence makes a compelling case for tryptophan overflow metabolism serving a cross-feeding or signaling function rather than a catabolic one. The finding is consistent with Fritts et al. (2021) and Ramoneda et al. (2023) who showed amino acid cross-feeding is widespread in soil communities and tryptophan auxotrophy is particularly common.

All 13 WoM-produced metabolites that could be mapped to GapMind pathways had "complete" pathway predictions, and all 13 also showed growth in FB experiments. This perfect agreement validates GapMind's accuracy for Pseudomonas fluorescens FW300-N2E3, consistent with Price et al. (2022, 2024). The matched metabolites are common amino acids and organic acids with well-characterized pathways.

The 94% mean concordance across four databases decomposes into: FB 21/21 = 100% (structural), GapMind 13/13 = 100% (structural), BacDive 3/7 = 43% (informative). Overall 37/41 comparisons are concordant (90.2%). A binomial test comparing BacDive utilization of WoM-produced metabolites (43%) against the species baseline (27.5%) shows no significant difference (p=0.40). The high concordance is largely inevitable given that FB always shows growth for metabolites used as sole C/N sources, and GapMind predicts complete pathways for common amino acids.

The top 18 genes significant across all 21 FB metabolite conditions are amino acid biosynthesis enzymes: homoserine O-acetyltransferase (methionine), ATP phosphoribosyltransferase (histidine), dihydroxy-acid dehydratase (branched-chain), isopropylmalate dehydrogenase (leucine), shikimate dehydrogenase (aromatic), imidazoleglycerol-phosphate dehydratase (histidine). These are essential for growth on any minimal medium. The ~370 genes significant in only 1-2 conditions are the truly substrate-specific ones. This distinction is critical for interpreting WoM↔FB integration.

Of 7,609 metal-important gene records across 24 organisms, 4,177 (55%) are sick under metal stress but have a <5% sick rate across 5,945 non-metal experiments (antibiotics, osmotic, carbon sources, etc.). The remaining 38% are "general sick" (important across many conditions) and 7% are "metal+stress" (shared with other stresses). This demonstrates that the Metal Fitness Atlas's metal-important gene set is not dominated by general stress response — the majority are genuine metal tolerance determinants.

Metal-specific genes are 84.8% core (pooled) vs 90.2% for general sick genes — a statistically significant difference (Cochran-Mantel-Haenszel p=0.011). Both categories are enriched above the 79.8% baseline. This partially supports the Metal Atlas's two-tier model: general stress response (Tier 1) is more core than specialized metal resistance (Tier 2), but both are predominantly core. The accessory genome contributes only modestly to metal resistance machinery.

Among the top novel candidates from the Metal Atlas, three stand out as metal-specific rather than pleiotropic: UCP030820/OG01015 (67% metal-specific, oxidoreductase, 7 metals), YebC/OG01383 (58%, transcriptional regulator/translation factor, 6 metals, 11 organisms), and DUF1043-YhcB/OG03264 (50%, cell division protein, 5 metals). In contrast, YfdZ (15%) and the Mla/Yrb system (0-25%) are pleiotropic — important for many conditions, not just metals. DUF39 (0%, sick rate 0.64) is a general fitness factor despite spanning 8 metals.

YebC was recently shown to be a translation factor for proline-rich proteins (Ignatov et al. 2025). Many metal homeostasis proteins (P-type ATPases CopA/ZntA, CDF transporters) contain proline-rich cytoplasmic loops. Hypothesis: YebC is specifically needed under metal stress because upregulation of proline-rich metal transporters creates a translation bottleneck that YebC resolves. Under non-metal conditions these transporters are not highly expressed and YebC is dispensable.

Initial analysis showed 0% metal-specificity for essential metals (Mo, W, Se, Mn), seemingly due to DvH's 608 non-metal experiments making specificity impossible. After fixing a locusId type mismatch that had silently excluded DvH, essential metals show 47-61% metal-specificity: Manganese (61%), Molybdenum (61%), Tungsten (57%), Selenium (46%). The experiment-count bias is real but less severe than initially thought.

Bacteria isolated from heavy metal contamination sites have metal tolerance scores a full standard deviation above the environmental baseline (Cohen's d = +1.00, Mann-Whitney p=0.006, n=10). The effect is dose-dependent: heavy metal (+1.00) > waste/sludge (+0.57) > all contamination (+0.43) > industrial (+0.20). This validates the Metal Fitness Atlas's genome-based prediction method against real-world isolation ecology. The signal holds within Pseudomonadota and Actinomycetota after phylogenetic stratification.

Species name matching (exact + GTDB suffix removal) links 42,227 BacDive strains (43.4% of 97K) to 6,426 GTDB pangenome species. The bridge enables cross-referencing BacDive phenotypic data with pangenome-derived predictions without Spark queries. The 56.6% unmatched strains reflect GTDB's different species boundaries from LPSN/DSMZ taxonomy.

Host-associated bacteria (n=12,086) have slightly but significantly higher metal tolerance scores than environmental bacteria (d=+0.14, p<0.0001). This contradicts the expectation that host niches have lower metal exposure. The likely explanation is genome size confounding: BacDive host-associated strains are dominated by Pseudomonadota pathogens with large genomes and correspondingly more KEGG-annotated gene clusters, inflating the normalized metal score.

Survey of DUF4041 (PF13250) in the 293K-genome BERDL pangenome found 4,572 gene clusters across 1,696 species and 33 phyla — far exceeding the >500 homologues reported in Saxton et al. 2026 (Nature). 86.7% are accessory or singleton genes, consistent with mobile defense island carriage. The patchy distribution across many phyla and families supports horizontal gene transfer.

The SNIPE nuclease domain belongs to Pfam family PF13455 (Mug113), not PF01541 (canonical GIY-YIG restriction enzymes/DNA repair). Both are in the GIY-YIG clan (CL0418) but are distinct families. This explains why zero gene clusters show DUF4041 + PF01541 co-occurrence — it's biological truth, not an annotation artifact. The paper describes the nuclease as "GIY-YIG" at the superfamily level, but never cites Pfam accessions. Verified via InterPro/UniProt analysis of the E. coli SNIPE protein (A0A0A1A5Z2: PF13250 at positions 232–333, PF13455 at positions 443–520).

The phagefoundry_strain_modelling database (separate from the GenomeDepot annotation browsers) contains experimental data from Gaborieau et al. 2024 (Nature Microbiology): 188 E. coli strains × 96 phages = 17,672 binary infection outcomes, plus an ML model (AUC=0.883) with SHAP importances for 1,582 gene cluster features. Lambdavirus 411_P1 (phage lambda) infects only 1/188 strains (0.5%), vs. 43.4% for Myoviridae — consistent with widespread ManYZ receptor loss making lambda-mediated infection rare.

Fitness Browser data (168 experiments, E. coli K-12 Keio collection) shows ManXYZ knockouts have severe fitness defects on D-mannose (fit = -3.93) and D-glucosamine (fit = -2.75) but are dispensable for D-fructose (fit = +0.18 to +0.66). This contradicts the UniProt annotation "fructose import across plasma membrane" (GO:0005354) for ManX. The mannose/glucosamine specificity is critical for understanding why SNIPE targets the ManYZ pore — it's the mannose transporter that phage lambda exploits for DNA injection, not a general sugar transporter.

The Fitness Browser contains one archaeal SNIPE protein in Methanococcus maripaludis JJ (locus MMJJ_RS01635), annotated with both PF13250 (DUF4041) and PF13455 (Mug113/GIY-YIG nuclease), plus PF10544 (DUF2525). This is a full two-domain SNIPE protein with 129 experiments of fitness data — the first SNIPE homologue with genome-wide knockout phenotypes available for analysis.

PhageFoundry Klebsiella genome browser contains 1 DUF4041 annotation (3 proteins at 558 aa — same length as E. coli SNIPE) and 4,619 PTS_EIIC (PF02378/ManY family) annotations. Klebsiella is the only PhageFoundry species with both SNIPE and the ManX-family PTS domain (PF00358). This is clinically relevant — SNIPE could affect phage therapy efficacy in this key pathogen.