Nature Microbiology

The archaeal phylum Nanobdellota (formerly Nanoarchaeota) was previously represented by four complete genomes. We present 208 complete Nanobdellota genomes from Oxford Nanopore metagenomes of the Baltic Sea water column and Fennoscandian groundwater (69-201 m below sea level), rotated to the ORC1/Cdc6 replication origin -- a 52-fold expansion of complete-genome representation. Across the ar53 supermatrix and a Nanobdellota-tuned 71-marker supermatrix on 1,239 taxa, the named GTDB orders within Nanobdellota are recovered as monophyletic clades, including the three orders that dominate our environmental sampling: Woesearchaeales, Pacearchaeales, and the GTDB placeholder order SCGC-AAA011-G17. This is consistent with the existing GTDB R232 order-level circumscription. We retire the SCGC-AAA011-G17 placeholder name, replacing it with a complete-genome-anchored SeqCode nomenclatural chain (Maxwellarchaeales ord. nov., Maxwellarchaeaceae fam. nov., Maxwellarchaeum gen. nov., and Maxwellarchaeum balticum sp. nov.) without altering the order-level circumscription. Pacearchaeales and Maxwellarchaeales retain no central or energy metabolism beyond Form III RuBisCO, PEP synthase, and ferredoxin; Woesearchaeales retains partial glycolysis and a V/A-type ATPase. A 4,262-tip phylogeny of rbcL (the RuBisCO large-subunit gene) identifies nine candidate archaea-to-Patescibacteriota Form III RuBisCO transfer events -- including one to a Baltic Minisyncoccia -- versus two reciprocal candidates, consistent with archaea-to-CPR being the more frequently identified direction in our data. All 256 Nanobdellota genomes (208 complete + 48 high-quality non-circular), the ar71 marker set with its 1,239-taxon ML tree, 154 Nanobdellota-trained HMMs for KEGG-ortholog detection in DPANN proteomes (94 ROBUST), and the 4,262-tip rbcL reference tree are released as a community resource, alongside the full analysis archive -- alignments, intermediate trees, structural predictions, and per-step scripts -- at Zenodo (DOI 10.5281/zenodo.20174424; see Using the resource).

Halogenated one-carbon (C1) compounds, such as dichloromethane (DCM), drive critical fluxes in global carbon and halogen cycles. While the genus Dehalobacter is canonically defined by obligate organohalide respiration, its physiological and ecological roles in anaerobic C1 metabolism have remained fundamentally ambiguous. Here, we document a paradigm-shifting metabolic capacity within a sediment-derived microbial consortium: the autonomous fermentation of DCM by a novel population, Candidatus Dehalobacter formatiformans strain J1. Over successive transfers, strain J1 outcompeted co-existing Dehalobacterium formicoaceticum to become the overwhelmingly dominant population (>80% relative abundance), converting DCM stoichiometrically to acetate and formate (4:1) without auxiliary substrates. Genome-resolved metagenomics revealed that strain J1 couples a distinct mec gene cassette--mediating methyl-transfer reactions during DCM activation--to a complete Wood-Ljungdahl pathway for efficient C1 assimilation. Crucially, strain J1 lacks the complete genetic repertoire for de novo cobamide biosynthesis. Physiological validation confirmed that this fermentative pathway is strictly dependent on exogenous cobamides, exposing a profound reliance on community cross-feeding. These findings reveal an unexpected acetogenic lifestyle within Dehalobacter, a lineage historically viewed as comprising obligate organohalide-respiring bacteria. More broadly, this work identifies cobamide-dependent methyl-transfer metabolism as an ecological control on anaerobic DCM fermentation and expands the known roles of Dehalobacter in carbon-halogen cycling in anoxic environments.

In a single Oxford Nanopore long-read metagenome from a Fennoscandian deep-groundwater borehole (KR0015B, Aspo Hard Rock Laboratory, Sweden), 791 protein clusters span at least one chromosomal contig and at least one co-sampled circular mobile element -- the cross-replicon LGT-candidate cohort. The 199 participating chromosomes are dominated by three small-genome / symbiont-associated lineages -- Patescibacteriota, Omnitrophota, and Nanobdellota -- but the per-chromosome participation rate tells a different story: Omnitrophota chromosomes participate at an order-of-magnitude higher rate (mean 56 cross-replicon clusters per genome), while Patescibacteriota and Nanobdellota dominate by compositional abundance only. Two large divergent circular mobile elements (233-kbp u20424375 and 123-kbp u29249220) -- each lineage-restricted within a single Omnitrophota genus, with sparse cross-phylum reach (only 12 of their combined 289 cross-replicon clusters involve a non-Omnitrophota partner) -- together account for 37% of the cohort and lack canonical plasmid or phage signatures. The 233-kbp element carries a Mu-class DDE transposase, is found integrated in one host chromosome at 99.3% nucleotide identity over 87% of element length, and carries an essentially complete bacterial big-operon r-protein cluster (31 r-protein KOs) as cargo with no rRNA genes -- a cargo profile with no published precedent in the mobile-element literature. Seven cross-replicon clusters span both domains; per-cluster phylogenies confirm gene-tree topologies that violate the species-tree expectation in 6 of 10 callable smoking-gun trees. We release the cross-replicon cluster table, integrated mobile-partner classifications, and chromosome taxonomy as a community resource. A parallel cross-chromosome catalog without the mobile-partner requirement contains 957 clusters, 95% of which carry no co-sampled circular plasmid or virus partner -- a chromosome-only LGT footprint that bounds the MGE-coupled cohort and is consistent with vehicle-free / direct-contact transfer in lineages whose close-contact symbiotic biology is well-documented.

Fungal hyphae form spatially confined interfaces in soil that mediate close associations with bacteria, collectively referred to as the hyphosphere. Despite its recognized ecological importance, experimental access to hyphosphere-associated microbial communities under realistic soil and plant-associated conditions has remained limited. Here, we present a soil-mimetic microcosm that enables controlled reconstruction and recovery of hyphosphere bacterial communities embedded within plant-associated soil. The system integrates field-derived soil, a native soil microbial inoculum, living cotton seedlings, and a spatially constrained fungal inoculum housed within sterile cell-strainer assemblies, permitting hyphal extension into soil while preserving a recoverable fungal-soil boundary. Using the soil-borne plant pathogen Fusarium oxysporum f. sp. vasinfectum as a model filamentous fungus, we show that the microcosm enables reproducible recovery of hypha-associated soil microaggregates containing physically attached bacterial cells. Full-length 16S rRNA profiling revealed pronounced reductions in bacterial richness and evenness in hyphosphere samples relative to bulk and rhizosphere soils, consistent with recruitment of a restricted subset of the surrounding microbiota. Ordination analyses demonstrated clear compositional separation between soil and hyphosphere compartments, with convergence of hypha-associated communities across bulk and rhizosphere contexts. Phylogenetic turnover analyses indicated phylogenetic structuring, whereas taxonomic analyses identified a conserved set of bacterial genera consistently associated with hyphae alongside compartment-specific taxa influenced by soil and plant context. Together, these findings establish the novel hyphal release-and-capture microcosm as a reproducible, ecologically grounded platform for studying hyphosphere-associated bacterial communities in plant-associated soils.

Identifying antibiotic resistance genes (ARGs) from metagenomic data is critical for studying antimicrobial resistance across microbial communities and pathogens. However, there is no standardized methodology for ARG annotation. Here, we compare ten commonly used ARG detection pipelines by analysing over 270 million prokaryotic genes from the Global Microbial Gene Catalogue across 13 distinct habitats. We observed up to a 45-fold difference in the number of reported ARGs, with a mean Jaccard index of only 16% between pipelines. Pipeline selection profoundly impacted downstream biological interpretations, with drastic changes to estimates of ARG relative abundance and richness, to the characterization of pan- and core-resistomes, and to the class-level composition of the inferred resistome. ARG detection pipelines make different, defensible trade-offs, and no single approach should be treated as authoritative. Therefore, users should justify and communicate choices carefully, as our analyses show that, taken uncritically, the same data can support conflicting biological and ecological interpretations.

Background Bacterial fitness is shaped by interactions between genome variation and environmental context, yet how these interactions determine its predictability and heritability remains unclear. In the clinically important pathogens of Klebsiella pneumoniae, a leading cause of hospital-acquired infections, this question is particularly pressing. Despite extensive genomic characterization, we still lack a systematic understanding of how genome-wide variation translates into fitness across diverse environments in K. pneumoniae. Methods We filled this gap by profiling a systematic collection of 1,462 clinical K. pneumoniae isolates across 214 diverse environmental and pharmacological stress conditions using high-throughput chemical genomics. Fitness was quantified from colony growth and integrated with whole-genome sequencing data. Genome-wide association analyses identified genetic determinants of fitness, and machine learning models incorporating genomic features were used to predict fitness.Results Fitness exhibited a strongly environment-dependent genetic architecture, with modest but significant concordance between genetic background and phenotypic variation. Under antibiotic and stress-combination conditions, fitness was driven by discrete, high-effect determinants, including known resistance genes, resulting in stronger signals and improved predictability. In contrast, non-antibiotic environments showed more polygenic and distributed architectures with weaker associations. Genome-wide analyses identified both established and previously uncharacterized genes linked with fitness across conditions. Resistance and virulence determinants exhibited clear context-dependent trade-offs, conferring fitness advantages under selection but imposing costs in non-selective environments. Consistent with this, plasmid carriage showed environment- and genotype-dependent fitness effects, with benefits under antibiotic pressure and measurable costs otherwise. Genomic variant-based models for fitness prediction achieved moderate performance (Mean Spearman correlation ({rho}) = 0.36 (95% CI: 0.18-0.67) for predicted versus observed values in unseen data) across conditions, with improved accuracy under strong antibiotic selective pressures, and produced well-calibrated prediction intervals with high coverage. Despite strong population structure effect on predictions, models captured predictive gene and SNP biomarkers for fitness. Conclusion These findings highlight that bacterial fitness is an emergent property of genome-environment interactions rather than a fixed attribute of genotype. This work establishes a unified high-dimensional genotype-phenotype framework linking genomic variation to fitness across diverse conditions in a major pathogen, with broader implications for other pathogenic bacterial species.

Bacterial signals control the development of marine algae, yet the molecular basis of these cross-kingdom interactions remains largely unknown. Thallusin is the paradigmatic case: isolated in 2005, it induces rhizoid and cell wall formation in the green seaweed Ulva at picomolar concentrations, but its biosynthesis has remained elusive for two decades. Comparative genomics across five bacterial phyla identifies a conserved set of genes - the eustigmatophyte bacterial operon (ebo) - as determinants of thallusin biosynthesis. Isotope labeling, heterologous expression, and gene deletion in Stieleria maiorica show that the aromatic scaffold derives from a cyclitol precursor and L-aspartate, with subsequent prenylation and cyclization. Searching 124,295 prokaryotic genomes identifies producers in eleven bacterial lineages, including soil cyanobacteria, establishing thallusin as a widespread cross-kingdom signal reaching beyond the ocean.

Microbes that remain uncultivated occupy nearly every ecosystem on the planet; this is particularly true in soils, where despite their prevalence, the roles of rarely cultivated microbes in driving biogeochemical cycles and ecosystem function remain poorly explored. We combine metagenome-informed substrate selection with enrichment sub-communities to generate reduced-complexity communities that preserve co-occurrence and expand experimental access to underrepresented soil lineages without requiring prior isolation of each member. Carbohydrate-active enzyme (CAZyme) profiles from soil-derived genomes were used to select carbon compounds predicted to enrich difficult to culture taxa, including members of the phylum Acidobacteriota. Based on 16S rRNA amplicon sequencing, we reproducibly enriched Terriglobus (Acidobacteriota) on multiple metagenome-guided substrates. Select communities with consistent presence and varying abundance of Terriglobus were passaged in a longitudinal design to generate 89 metagenomes; genus-level profiling revealed that community composition varied between biological replicates but remained consistent within replicates over time, providing diverse Acidobacteriota-containing configurations for downstream analysis. Association network inference identified a core set of co-occurring taxa that positively tracked with Terriglobus across the longitudinal series. In parallel, the substrate-guided approach led to isolation of a novel Terriglobus species, the first cultured representative of its GTDB species cluster. Together, these results establish a generalizable strategy for generating communities enriched with rarely cultivated taxa, yielding tractable systems for studying microbial interactions and community assembly in soil.

During infection, pathogenic mycobacteria damage the membrane of the Mycobacterium-containing vacuole (MCV), triggering host repair responses that preserve an intracellular permissive niche before bacteria escape to the cytosol at later stages. How the MCV transitions from repairable injury to catastrophic rupture remains poorly understood. Here, we dissected the respective contributions of the ESX-1 effectors EsxA/EsxB and the cell-envelope lipid phthiocerol dimycocerosate (PDIM) during Mycobacterium marinum infection of the amoeba Dictyostelium discoideum. Combining host reporters for membrane damage and repair with single and double bacterial mutants, we show that EsxA/EsxB and PDIM are both required for full intracellular virulence but act at distinct stages of MCV damage progression. Loss of EsxA/EsxB strongly reduced recruitment of ESCRT and autophagy reporters to the MCV, demonstrating that EsxA initiates repairable membrane lesions. In contrast, PDIM-deficient bacteria retained the ability to recruit early damage reporters and ESCRT machinery but showed reduced autophagy-associated repair, failed to efficiently acquire cytosolic perilipin coating, and remained largely confined within the MCV. Genetic disruption of host autophagy restored cytosolic access and intracellular growth of PDIM-deficient bacteria, indicating that PDIM is specifically required to overcome host repair capacity rather than to initiate damage. Importantly, the sequential requirement for EsxA and PDIM was conserved during infection of murine microglial BV-2 cells. Remarkably, PDIM-defective mutants induced lysenin recruitment, a reporter of sphingomyelin exposure, but progression to autophagy engagement was strongly decreased. Together, our results support a two-step model in which EsxA initiates MCV membrane damage, while PDIM amplifies these lesions towards catastrophic rupture, enabling escape to the cytosol and dissemination.

Cryptococcus neoformans and Cryptococcus gattii are major causes of fungal pneumonia and meningitis, frequently co-occurring with Mycobacterium tuberculosis in endemic regions, where co-infection is associated with increased mortality. Yet, how Cryptococcus adapts to mycobacterial co-presence within the lung remains poorly understood. Here, we show that mycobacterial cues trigger a conserved adaptive programme in C. gattii, mirroring responses previously observed in C. neoformans. Increasing exposure to mycobacteria drives cell and capsule enlargement and promotes titan cell formation, accompanied by dose-dependent remodelling of chitin and chitosan. Importantly, in vivo exposure to heat-killed mycobacteria increases C. gattii pulmonary burden, linking structural remodelling to enhanced persistence. These findings identify mycobacterial co-presence as a driver of fungal phenotypic plasticity and reveal pathogen-pathogen interactions as critical regulators of disease outcome, highlighting a previously unrecognised axis of co-infection relevant to C. gattii pathogenesis and therapeutic strategy.

The gut virome represents a vast reservoir of genetic diversity with profound implications for human health, yet it remains the "dark matter" of the microbiome due to the staggering complexity of reproducible viral profiling. It remains fundamentally contested whether biologically informative virome signals can be robustly recovered from routine whole-metagenome sequencing (WMS), and to what extent these signals offer ecological insights independent of the bacteriome. Here we present VIP2B, a framework that leverages Type IIB restriction tags to extract multifaceted viral features (encompassing taxonomy, coverage, function, and phenotype) directly from bulk WMS data. Through extensive benchmarking across incomplete references, unseen genomes, and high bacterial or host background, we demonstrate that VIP2B achieved high precision and robust taxonomic concordance. By applying VIP2B to paired bulk and virus-like particle (VLP)-enriched datasets, we reveal a species-level overlap far greater than previously recognized, proving that standard bulk metagenomes contain a wealth of recoverable viral information. Analysis of 20 clinical cohorts demonstrates that coverage-, function-, and phenotype-resolved viral features consistently identify disease-associated signatures that escape taxonomic analysis alone, significantly improving diagnostic models over bacteriome-only approaches. Finally, we define two distinct gut virome community states at the population scale (n=6,090), characterized by divergent diversity profiles and health associations. Our findings establish the gut virome as a non-redundant, clinically actionable component of the human holobiont and provide the methodology necessary to transition microbiome research toward a truly multi-kingdom framework.

Entamoeba histolytica (Eh) is a formidable intestinal pathogen, yet the ecological principles governing its invasion of the gut microbiome remain elusive. Upon colonization, Eh encounters resident bacteria typically sequestered within aggregates and biofilms. While Eh utilizes cysteine proteinases to degrade biofilm matrices and access bacterial prey, the strategies bacteria employ to sense and evade this predation are largely unknown. Here, we identify a metabolic signalling axis that allows the probiotic bacterium Bacillus subtilis to perceive and respond to predatory Eh. In the absence of mitochondria, Eh relies on fermentative glycolysis, using alcohol dehydrogenase to produce distinct metabolic byproducts. Using quantitative proteomics and single-cell imaging, we demonstrate that B. subtilis detects the Eh-derived metabolite acetaldehyde as a proxy for predator presence. By mapping the acetaldehyde-responsive regulatory network, we show how this metabolic input is transduced to control the motility machinery, while our data suggest that the broader predatory secretome acts as a multi-modal signal influencing multiple bacterial physiological programs. This chemical cue triggers a rapid phenotypic switch in B. subtilis, driving a transition towards a motile, planktonic "flight" response. Our findings reveal that commensal bacteria exploit the unique metabolic signature of anaerobic parasites to coordinate defensive behaviours, highlighting how inter-kingdom signalling shapes microbiome architecture during infection.

Mechanistic understanding of gut ecology is limited by the availability of tools for precise manipulation of microbiome composition. Here, we isolate lytic phages to enable targeted removal of gut commensal Escherichia fergusonii (Ef) from complex, undefined stool-derived in vitro communities. A single phage drove resistance without fitness cost in monoculture, but resistant Ef exhibited reduced fitness in communities, enabling expansion of closely related Proteobacteria. Resistance arose via reversible promoter inversion linked to outer-membrane function. A phage cocktail overcame resistance to achieve Ef knockout across communities with minimal collateral effects. Using knockout communities, we show that Ef is necessary and sufficient for preventing Salmonella invasion. Replacement with an Ef transposon-mutant library revealed that community-specific fitness defects are enriched in genes involved in outer-membrane assembly. Disruption of these genes sensitized Ef to antagonistic community members, highlighting interspecies warfare as a key driver of microbiome ecology. These results establish phage-mediated perturbation as a framework for linking species to community-level function and for enabling precision microbiome engineering.

Using a longitudinal cohort of 633 Gambian children (IHAT-GUT, NCT02941081), we resolve two mechanistically distinct ecological pathways linking Prevotella stercorea to infection risk. Its abundance positively predicts gut microbiome richness, consistent with community-level colonisation resistance for enteric outcomes. However, its association with reduced acute respiratory infection (ARI) persists unchanged after richness adjustment, identifying a species-autonomous pathway independent of community diversity. Weight-for-age z-score (WAZ) is uncorrelated with microbiome richness within strata, supporting WAZ as a proxy for host immune-metabolic reserve rather than a determinant of microbiome composition. In Low-WAZ children, P. stercorea at Day 1 associates with suppressed CRP, whereas in higher-WAZ children, elevated Day 1 inflammation predicts subsequent P. stercorea colonisation at Day 85, consistent with host-context-dependent immune selection. ARI and fever protection is richness-independent and concentrated in Low-WAZ children. P. copri does not retain an independent protective association when modelled jointly. These findings have direct implications for microbiome-directed interventions.

Despite intense interbacterial antagonism mediated by mechanisms such as the type VI secretion system (T6SS), pathogenic Acinetobacter frequently persist within highly competitive polymicrobial infections. How these pathogens navigate such hostile environments to achieve co-existence remains poorly understood. Here, we show that pathogenic Acinetobacter employ distinct, multifaceted strategies to resist elimination by both distantly related competitors and closely related kin. T6SS-active strains outcompete heterologous bacteria by deploying a large and diverse repertoire of antibacterial effectors. In contrast, some naturally T6SS-deficient strains resist exogenous T6SS attacks by elaborating a unique, high-density polysaccharide capsule (KL34) that functions as an effective physical shield. Most intriguingly, we uncover a mechanism that prevents lethal competition among kins. A conjugative multidrug-resistant plasmid encoding T6SS repressors is transferred into aggressive strains upon T6SS-mediated attack, leading to suppression of their antibacterial activity. We also found that conjugation is induced by T6SS attack, which effectively suppresses attacking kin and promotes co-infection in vivo. Together, these findings reveal a dynamic and multilayer defense program that enables Acinetobacter to withstand interbacterial warfare while facilitating co-existence. Our study establishes a paradigm in which damage-triggered plasmid transfer enforces targeted suppression, reshaping microbial interactions in polymicrobial communities.

Bacterial persisters are frequently described as metabolically dormant, yet the endogenous metabolic programs that sustain survival during prolonged nutrient limitation remain poorly understood. Here, using stationary-phase Escherichia coli as a model of antibiotic tolerance, we combine proteomics, genetics, metabolic phenotyping, and single-cell imaging to define a metabolic framework underlying persistence. Perturbation of tricarboxylic acid cycle function broadly reprogrammed stationary-phase physiology, suppressing lipid and glycerol metabolism, altering energy homeostasis and proteostasis, and reducing antibiotic tolerance. Systems-level analyses identified phospholipid-derived glycerol catabolism as a central metabolic node linking endogenous carbon recycling to persistence. Genetic disruption of glycerol utilization impaired proton motive force homeostasis, reduced formation of large polar protein aggregates, altered division-associated remodeling, and sensitized cells to antibiotic-induced lysis. Functional metabolic assays further revealed that persisters retain a selective capacity to utilize glycerol for rapid proton motive force restoration without growth resumption. Together, our findings support a model in which stationary-phase persisters are not metabolically inert but sustained through endogenous metabolic rewiring that coordinates energy maintenance, proteostasis, and antibiotic tolerance.

The rise of antibiotic-resistant bacterial infections has driven renewed interest in bacteriophage therapy, where viruses that specifically kill bacteria are used as targeted antimicrobials. Pseudomonas aeruginosa, a WHO critical-priority pathogen that causes severe infections in hospitalized and immunocompromised patients, presents a major challenge for phage therapy because of its extraordinary genetic diversity. Phages effective against one bacterial strain often fail against others, and existing cross-resistance-profiling approaches require iterative empirical testing of each new patient isolate. To establish a genome-based framework for rapid phage-isolate matching, we assembled a collection of 95 genomically diverse P. aeruginosa phages representing 20 genera and tested each against 99 genetically diverse clinical isolates, generating 9,405 infection outcome measurements. Bacterial O-antigen serotype emerged as the dominant determinant of strain susceptibility, while defense systems, anti-defense systems, and prophage burden contributed smaller strain-specific effects. The full curated multivariate model explained 47% of strain-susceptibility variance. Machine-learning models integrating these features and pangenome-derived gene clusters reached a per-strain AUROC of 0.86. In an in vivo proof-of-concept test against a single held-out strain, the ML-designed cocktail produced a [~]12-fold greater median CFU reduction than the expert-designed cocktail (q = 0.045), with both cocktails substantially reducing burden relative to the untreated control ([~]113-fold for ML, [~]9-fold for CG; both q < 10{square}3). SHAP analysis of the model identified bacterial surface-architecture genes (LPS biosynthesis, outer membrane proteins, type IV pili) as the dominant predictors, with defense-system content modulating which specific phages succeed against a strain rather than uniformly damping susceptibility. Together, these results establish a genome-based framework for predicting phage susceptibility in genetically diverse clinical isolates.

Host-associated lipids shape plant-microbiome interactions, but their microbiome-mediated turnover and role in pathogen exclusion are not fully understood. In tomato, lauric acid (C12:0) occurs across root-associated compartments, and its abundance at the root-soil interface is linked to soil-dependent differences in rhizosphere community composition and Ralstonia solanacearum colonization. Lauric acid promotes Ralstonia motility and virulence in vitro while inhibiting some beneficial lauric-acid-sensitive taxa, especially Gram-positive antagonists. In disease-suppressive soils, rhizosphere communities enriched in lauric-acid-degrading taxa are associated with lower local lauric acid levels and reduced pathogen colonization, suggesting community-dependent buffering of the rhizosphere lauric acid pool alongside other protective microbiome functions. Soil perturbation, microbiome transplantation, gnotobiotic SynCom reconstruction, and isotope tracing provide convergent evidence that microbiome-mediated lauric acid turnover contributes to colonization resistance and helps explain how rhizosphere lipid chemistry influences pathogen invasion outcomes in tomato, revealing an ecologically grounded protective mechanism for pathogen management.

Microbes that span environmental reservoirs and diverse human infections are often described as generalists or as ubiquitous, yet ecological theory predicts generalism should be unstable when specialists outperform within any one niche. Here we show that Pseudomonas aeruginosas apparent ecological breadth reflects convergent, cryptic specialism (CCS) - repeatable, environment-linked genomic differentiation that is not confined to deep lineages - rather than strict specialism or generalism. An analysis of 6,627 genomes with source-environment metadata reveals that environments are broadly dispersed across the phylogeny, inconsistent with lineage-locked specialization. Despite this shallow phylogenetic structure, genome content predicted environment-of-isolation across nine genotype-discernible environments, including under cross-validation that blocks phylogenetic relatedness. Interpretable feature profiles recovered both shared and environment-specific signals, including genomic signatures distinguishing distinct chronic and acute human infections. Finally, phenotypes from 47 diverse strains clustered more strongly by environmental source than by phylogenetic relatedness. Together, these results indicate that widely distributed bacterial "generalists" can comprise mixtures of cryptic, convergent specialists. By mapping genotype-defined ecological structure, our approach can identify when apparent generalists harbor hidden structure relevant to infection risk.

The continual advancement of genetic tools has been critical to our modern understanding of bacteria, with transposons, plasmids, and homologous recombination becoming workhorses of molecular microbiology. However, precisely specified reverse genetic approaches remain painstakingly slow and inaccessible, particularly in non-model strains. This reality is exemplified by the opportunistic pathogen, Pseudomonas aeruginosa (Pa), where conventional allelic exchange remains the dominant reverse genetic method. Here, we adapt a rapid genetic toolkit for use in Pa, relying directly on commercially available oligonucleotides (120 bases) to create precise genomic mutations through homologous recombination (i.e. oligo recombineering). Oligo Recombineering followed by Bxb-1 Integrase Targeting (ORBIT) uses a short attachment site for an integrating plasmid, which provides traditional antibiotic selection and can also carry flexible cargo. We establish Pa ORBIT works effectively for gene deletion without off target mutations, optimize protocol parameters (e.g. oligo length, electroporation), and demonstrate markerless and clean deletions. Importantly, our toolkit works well in clinical Pa strains as demonstrated by constructing efflux pump deletions in three different isolates. To test the high throughput capabilities of Pa ORBIT, we created over 160 degron-based hypomorphs (i.e. knockdowns) across 43 essential proteins in a pooled mutant library. Upon screening this library with and without antibiotics, we identify highly vulnerable essential proteins and hypomorphs that display synergy with clinical drugs. Therefore, ORBIT can be used for cutting edge low and high throughput investigations in this priority pathogen, setting the stage for answering critical basic and clinical science questions. SignificanceTo understand bacterial genomes, researchers need access to rapid, flexible, precise and high throughput genetic perturbation tools. Here we present an oligonucleotide-based method that satisfies these requirements for use in the opportunistic pathogen, Pseudomonas aeruginosa. By relying on oligos to encode genomic homology arms, no molecular cloning is required - making these tools rapid, robust, and scalable. We benchmark gene deletions in both lab and clinical strains, opening the possibility of rapid genetic studies across the P. aeruginosa pangenomic space. At high throughput, we use an oligo pool to create a mutant library of degron tagged essential proteins. These knockdowns (i.e. hypomorphs) show certain essential genes are highly vulnerable and others are synergistic with clinical drugs, providing insight into future antibiotic and co-therapy development.