It has been proposed that a defining distinction between viruses and cells lies in the absence or presence of ribosomal genes, respectively. Recent studies revealing that viruses occasionally encode ribosomal proteins (RPs) have challenged this view. However, so far, only viral genomes with up to three RPs have been discovered. Here, we perform a functional genome analysis of the Microcystis jumbo phage PhiMa05 and show that it encodes six RPs, an RP acetyltransferase, and a ribosome biogenesis protein. To our knowledge, this makes PhiMa05 the first cyanophage reported to encode RPs, as well as the virus with the most comprehensive RP-coding set of the known virosphere. Evolutionary analyses suggest that these viral RP-coding genes may have been horizontally transferred from a temperate ancestor of PhiMa05 to certain members of the Vampirovibrionia, a non-photosynthetic basal lineage of Cyanobacteriota, via the integration of the viral genome. We find that four RPs, the RP acetyltransferase, and the ribosome biogenesis protein of the PhiMa05-like prophages are the only copies of those proteins that the near-complete genomes of some Vampirovibrio hosts possess. We hypothesize that such cellular organisms may depend on the PhiMa05-like prophage for protein synthesis, and hence life itself. Collectively, our results provide evidence for the existence of viruses with particularly enriched sets of RP-coding genes and indicate that, in some cases, such viral genes have been transferred to cells, potentially becoming essential for the survival of the host.
The candidate phylum Cloacimonadota is frequently detected in anoxic environments such as anaerobic digestion (AD) reactors, hydrothermal vents, and deep-sea sediments, yet its metabolism remains poorly understood. Metagenomic evidence suggests capacities for amino acid fermentation, carbohydrate degradation, as well as a potential role in syntrophic propionate oxidation (SPO), a key bottleneck in AD. However, a complete methylmalonyl-CoA (mmc) pathway, central to SPO, has not been previously identified in Cloacimonadota genomes. Here, we report results from an acidified lab-scale anaerobic baffled reactor fed with sugar beet pulp, where an increase in the relative abundance of Cloacimonadota correlated with recovery of methanogenesis, resulting in increased methane content in the produced biogas. Metagenomic and metatranscriptomic analyses enabled metabolic reconstruction of the dominant Cloacimonadota operational taxonomic unit (OTU). Furthermore, using a curated database of 204 genome-resolved Cloacimonadota species, we characterized the phylum-level metabolic potential. Comparative genomics revealed alternative proteins, including 2-oxoglutarate:ferredoxin oxidoreductase and aspartate aminotransferase, likely to substitute for missing enzymes in the classical mmc pathway. These proteins were widely distributed and highly conserved across the analyzed Cloacimonadota genomes, suggesting that this variant of the SPO pathway could represent a phylum-specific trait. Moreover, we hypothesize that these alternative pathway steps may link propionate metabolism to protein degradation and poly-γ-glutamate biosynthesis. Network analysis identified the methanogenic archaeon Methanothrix as a potential syntrophic partner, an interaction further supported by propionate-fed enrichment cultures showing co-occurrence of Cloacimonadota and Methanothrix species. Our study sheds light on the Cloacimonadota metabolism, advancing our understanding of their ecological roles and potential for biotechnological applications.
Phage therapy offers a promising alternative to antibiotics for treating multidrug-resistant infections. Plasmid-dependent phages (PDPs) are particularly attractive as therapeutics because they can both kill targeted pathogens and prevent the further spread of antibiotic resistance genes encoded by plasmids. However, the evolutionary trajectories of multidrug-resistance (MDR) plasmids under the selective pressure of PDPs remain poorly understood, particularly in eco-evolutionary contexts that remain permissive to plasmid conjugation. We experimentally evolved populations of Escherichia coli carrying the MDR plasmid RP4 in the presence of the plasmid-dependent phage PRD1 under conditions where the benefits of conjugation were either strong or weak. When opportunities for conjugation were rare, PRD1 only transiently suppressed the conjugative plasmid population due to the rapid evolution of phage-resistant plasmids lacking conjugative ability. Increasing ecological opportunities for conjugation enhanced plasmid suppression and delayed the evolution of phage-resistant plasmids. PRD1 resistance was associated with plasmid loss and reduced conjugative ability, although this trade-off was complex because resistance mutations had heterogeneous effects on pilus production and conjugation. Mutations and IS-mediated inactivation in conjugation genes generated a spectrum of resistance phenotypes, from partial resistance (trbB, trbL) to complete resistance (virB4/trbE). Bioinformatic analysis of publicly available IncP plasmids revealed frequent truncations of the VirB4/TrbE protein, suggesting that plasmid-dependent phages may represent an important selective pressure shaping plasmid evolution in natural populations. Our results demonstrate an evolutionary trade-off between conjugative ability and phage resistance that cannot be easily circumvented by plasmids. Targeting multidrug-resistance plasmids with PDPs is likely to drive loss of conjugation, limiting the transfer of antibiotic resistance genes in microbial communities.
Symbiotic associations between microorganisms often involve eukaryotes partnering with microbes for nutrient exchange, protection, and resource acquisition. Bacterial lineages like the Chlamydiota have evolved entirely symbiotic lifestyles, exploiting their eukaryotic hosts for energy, diverse metabolites, and shelter. The study of environmental chlamydiae - outside the well-studied vertebrate host range - has revealed diverging interactions on the mutualism-parasitism spectrum. This highlights their potentially important roles in host-microbe interactions underscoring the relevance of obtaining isolates from diverse environments and hosts. Here, we describe an isolate of a chlamydial symbiont of the freshwater cnidarian Hydra. The symbiont could be isolated and stably maintained in insect cell lines and represents a member of the recently described family-level lineage Chlamydiae Clade III for which we propose the name Endochlamydiaceae. Fluorescence and electron microscopy reveal the symbiont morphology and its endodermal location. Comparative genomics shows the isolate, named Endochlamydia hydrae, encodes a conserved set of genes involved in host invasion, communication, and pathogenicity. Instead of displaying unique genomic adaptations to its animal host, E. hydrae shows signs consistent with ongoing genome reorganisation and streamlining, suggesting a more recent host shift. Screening for closely related 16S rRNA gene sequences in public environmental microbiomes also indicates a broader host range. Moreover, exploration of environmental Hydra oligactis populations revealed they might serve as host for a wider spectrum of chlamydial species. This study highlights the evolutionary success of chlamydiae and their genomic toolkit to infect a wide range of hosts and their ecological significance by interacting with diverse organisms.
Microorganisms are metabolically versatile and central to marine ecosystems, yet the potential of marine microbial communities to degrade different bioplastics and the effect of environmental factors are poorly understood. Employing multi-seasonal in situ and in vitro experiments, we assessed the biodegradation of six commonly used bio-based bioplastic materials at a coastal site in the brackish Baltic Sea and characterized the associated microbial communities using metagenomics and metatranscriptomics. Cellulose acetate (CA), polybutylene succinate (PBS), and polyhydroxybutyrate/valerate (PHB) degraded at varying rates across materials, seasons, and experimental settings, with up to 28% weight attrition after 97 weeks in situ (CA) and 56% carbon loss as CO2 after 4 weeks in vitro (PBS). The three biodegraded plastics developed similar microbial communities that differed markedly from those on the other materials (cellulose acetate propionate, polyamide, and polyethylene) and in the water column. The main microbial populations on the biodegraded plastics included aerobic and facultative anaerobic heterotrophs with a broad capacity for carbohydrate metabolism. Populations with the potential for nitrogen fixation and denitrification were more prevalent on the biodegraded plastics, suggesting that bioplastic biodegradation is constrained by and coupled to the marine nitrogen cycle. Based on the metatranscriptomic signal of key genes involved in the initial hydrolysis of CA, PBS, and PHB, we identified diverse microbial populations that can potentially drive the biodegradation of these materials in the Baltic Sea, many of which encoded the potential to degrade multiple bioplastics. We propose the term 'bioplastisphere' to denote the distinctive microbial communities associated with biodegradable plastics.
Associations with microbial symbionts shape the ecology and evolution of almost all eukaryotes. One of their defining features is their specificity, but despite this, many symbioses show a degree of flexibility, with some symbiont species capable of colonizing multiple (often closely related) host species. Although widespread, the functional and evolutionary consequences of flexibility in host-symbiont pairings are poorly understood. Bivalves from the diverse, globally distributed, and ecologically important family Lucinidae are ideal for investigating this, as multiple host species can associate with the same symbiont species, often at the same location. We used metatranscriptomics to investigate the molecular responses of one symbiont species, Candidatus Thiodiazotropha endolucinida, in association with three different host species that co-occur in seagrass meadows in the Caribbean Sea. In replicated experiments, we identified host species-specific patterns of symbiont gene expression including those for key functions such as carbon fixation, cell division, and sulfide oxidation. Our work shows that the symbiont consistently responds in different ways to association with different host species. Because all samples were collected at the same site on the same day, and were thus exposed to the same environmental conditions, these differences are likely driven by host rather than environmental factors. In addition, host species had significantly different carbon isotope signatures, which were consistent with distinct modes of host-microbe interaction indicated by transcriptomics. Our results show that not only symbiont genotype, but also symbiont phenotype may enable coexistence of closely related host species, demonstrating the power of symbiosis in promoting and maintaining biodiversity.
Despite rapid advances in characterizing the human microbiome, the ecological pressures shaping its transitions from healthy to diseased states remain poorly resolved. This is particularly true for periodontitis, a slow-progressing chronic inflammatory disease associated with well-defined shifts in the subgingival microbiome. Here, we report the development of a complex synthetic community model of the subgingival microbiome, designed for systematic interrogation of ecological factors that drive community restructuring. The model includes 22 prevalent and abundant subgingival species maintained in mucin-rich medium under microaerophilic, continuous culture conditions, in a chemostat. Using this system, we interrogated the impact of serum, as a surrogate for the inflammatory exudate produced by the host in response to biofilm accumulation, on community structure and function. Through integrated 16S rRNA gene sequencing, metatranscriptomics, and metabolomics, we found that serum was not required for a community with a periodontitis-like configuration to establish, but its presence intensified features of dysbiosis. Serum increased total biomass, promoted polymicrobial aggregate formation, promoted nitrogen and protein metabolism thereby modifying the environmental pH towards alkalinity, and introduced nitrosative stress. Serum also modified the community metatranscriptome in ways that paralleled microbiome activities in human periodontitis. Serum, however, decreased community diversity by disproportionally conferring a competitive advantage to the pathogen Porphyromonas gingivalis. This synthetic community model has revealed serum as a key nutritional pressure that modulates subgingival microbiome ecology and may perpetuate dysbiosis.
Microbial secondary metabolites have been recognized and utilized for nearly a century. Nevertheless, the eco-evolutionary mechanisms governing their distribution among microorganisms remain largely unresolved. In this study, we examined intraspecific interactions within Streptomyces albidoflavus and identified a strain exhibiting potent antagonistic activity against conspecifics. This "killer" phenotype was attributed to the production of kosinostatin, a hybrid aromatic polyketide antibiotic. Evolutionary genomic analyses provided strong evidence that the kosinostatin biosynthetic gene cluster was horizontally acquired in S. albidoflavus over a relatively short evolutionary timescale, a finding consistent with its sparse distribution within this species, across the genus Streptomyces, and even throughout the phylum Actinomycetota. Using microcosm assays, we demonstrated that the kosinostatin producer outcompeted sensitive conspecifics in liquid culture but not in soil, indicating that environmental context plays a key role in altering the fitness benefits of this cluster. Moreover, the competitive advantage was observed only in the presence of sensitive strains, revealing a trade-off between fitness benefits and metabolic costs. These results highlight the role of context-dependent selection in shaping the evolutionary persistence of the kosinostatin cluster. The current distribution pattern of this cluster in S. albidoflavus likely results from a dynamic interplay of intraspecific horizontal gene transfer, vertical inheritance, and recurrent gene loss. Overall, our findings establish an eco-evolutionary framework that explains the rarity of a potent antibiotic gene cluster in Streptomyces, illustrating how environmental constraints, fitness trade-offs, and gene flux collectively orchestrate the biosynthetic architecture of Streptomyces species.
Reactive oxygen species (ROS) are essential for cellular signalling and redox homeostasis, but their accumulation causes cellular oxidative stress. In inflammatory bowel disease, oxidative stress is linked to chronic inflammation and alterations in the gut microbiota. We hypothesised that these alterations may result from the impact of ROS on the interactions between bacteria and their viruses, bacteriophages. We followed the evolution of three Escherichia coli strains and a virulent bacteriophage in a chemostat under continuous growth and studied the impact of oxidative stress on this community. We show that both the bacteriophage and its three hosts persisted in the system over 10 days, but the relative abundance of bacteriophages was decreased in the presence of ROS. Oxidative stress also limited bacteriophage population diversity by favouring the selection of specialist bacteriophages with a narrower host range. Concomitantly, ROS accelerated the evolution of bacterial resistance to bacteriophages and drove the fixation of genomic mutations in genes related to cell surface structures or located in mobile genetic elements. These results highlight that oxidative stress impacts the evolutionary dynamics between bacteria and bacteriophages with consequences for microbiota diversity and potential implications in the context of intestinal inflammation.
Rhizopus microsporus is a major cause of mucormycosis, an infection caused by Mucorales that increasingly affects immunocompromised individuals. Certain isolates of R. microsporus harbor bacterial endosymbionts that regulate key fungal functions, particularly asexual and sexual reproduction, but these effects have been explored exclusively in environmental isolates. Although some clinical isolates contain Mycetohabitans endosymbionts, their influence on fungal reproduction remains unknown. This dependence on endosymbionts for asexual spore formation in environmental isolates has established the Rhizopus-Mycetohabitans association as a model for studying fungal-bacterial endosymbiosis, but it has also constrained comparative studies across environmental and clinical backgrounds. We show that light exposure partially restores asexual sporulation in endosymbiont-cured environmental strains, enabling the generation of isogenic sporulating lines. Transcriptomic analyses revealed that both light and endobacteria modulate overlapping signal transduction pathways, regulating the expression of conserved genes involved in asexual development in Mucorales and other fungi. Functional assays demonstrated that asexual spores from cured strains are viable; however, the presence of endosymbionts accelerates spore formation, enhances osmotic stress tolerance, and helps maintain cell-wall integrity. Cured strains exhibit altered membrane composition, including reduced ergosterol levels, which may contribute to their resistance to macrophage phagocytosis. Despite these compensatory adaptations, cured strains showed attenuated virulence in a murine mucormycosis model, highlighting the role of bacterial endosymbionts in fungal pathogenicity. The discovery of light-induced sporulation in cured strains provides a valuable experimental framework for future comparative studies requiring asexual spores, offering new opportunities to explore the role of fungal-bacterial endosymbiosis in fungal biology and human disease.
Shipworms (Bivalvia: Teredinidae) are the most prolific wood consumers in marine environments. These wormlike marine bivalves digest wood using carbohydrate-active enzymes (CAZymes) produced by intracellular bacterial endosymbionts housed within their gills. Although several shipworm species are known to host multiple co-occurring symbiont species, the factors that influence symbiont community assembly, including the phylogenetic identity and metabolic capabilities of the symbionts, remain poorly understood. We sequenced gill symbiont metagenomes from multiple specimens of two shipworm species, Teredo bartschi (22 specimens) and Lyrodus pedicellatus (14 specimens), which have sympatric distribution in the wild, and which were reared together in laboratory co-culture. From these metagenomes, we assembled 90 metagenome-assembled genomes representing seven distinct symbiont species. The metagenome of each host specimen contained between one and five symbiont species, with each including at least one nitrogen-fixing symbiont. Six of the seven identified symbiont species were found in both host species, demonstrating a lack of host species specificity in these symbioses. We identified patterns of symbiont occurrence and co-occurrence in these two hosts and used these patterns to constrain the core set of CAZyme and nitrogen-fixation gene classes necessary to support host survival. Our results indicate that, in these two host species, symbiont community composition reflects the symbionts' capabilities for carbohydrate degradation and nitrogen fixation, rather than strict species-specific mechanisms of host and symbiont sorting.
Seagrasses support immense biodiversity and are critical for maintaining coastal ecosystem health. These foundation species benefit from a 'three-way' facultative relationship with one of the common inhabitants of seagrass meadows, lucinid bivalves, which host specific bacterial Ca. Thiodiazotropha symbionts. Relatives of the bivalve symbionts have been detected on seagrass roots raising the possibility that these symbionts may colonize both animals and plants; however, no study has yet compared bivalve- and seagrass-associated symbionts at the same site and time. Our combination of 16S rRNA gene amplicon and metagenome sequencing revealed a greater diversity than was previously observed within both lucinid bivalves and on seagrass roots from the Adriatic Sea and resulted in the closed genome of one prominent symbiont species. We show that two of the Ca. Thiodiazotropha ASVs found on seagrass roots are identical to those found in bivalve hosts at the same site. This suggests that symbiont sharing may occur in the seagrass habitat between these two host species, which has important evolutionary and ecological implications for both hosts and symbionts.
Gut microbial communities often differ at the strain level among individual hosts, but the mechanisms driving this variation remain poorly understood. One potential factor is "priority effects", a process in which differences in the timing and order of microbial colonization influence subsequent community assembly ("first come, first served" dynamics). We hypothesize that priority effects operate at the strain level within species, where closely related bacteria exhibit niche overlap, and that these dynamics can lead to community divergence even under similar environmental conditions. We tested these predictions, using the gut microbiota of honeybees, which harbor conserved microbial communities that differ in strain composition among individual bees. We sequentially colonized microbiota-depleted honeybees with two distinct microbial communities composed of the same 12 core microbiota species but different strains, ensuring that individuals shared species-level composition but differed at the strain level. We found that firstcomer strains consistently dominated the resulting communities, suggesting strong priority effects. Dropout experiments in which the firstcomer strain of a species was removed led to only partial increases in the colonization success of the conspecific latecomer, suggesting that both intra- and inter-species interactions contribute to priority effects. Our findings highlight the significant role of priority effects in strain-level community assembly and reveal their influence in shaping the specialized gut microbiota of honeybees, with important implications for the development of probiotic strategies in beekeeping.
The root nodules formed by rhizobia and leguminous plants are specialized structures for nitrogen fixation. However, a large number of non-rhizobial endophytes also coexist within the nodules, and their contribution to nitrogen fixation under abiotic stress conditions remains unclear. Here, using the wild leguminous shrub Sophora davidii as model system, we identified an important NRE (Bacillus siamensis BT-9-1) by analyzing keystone taxa within the bacterial cooccurrence network of root nodules. This strain could improve the survival of Mesorhizobium metallidurans YC-39 under saline-alkali stress. A mechanistic investigation revealed that the expression of ilvA, ilvH, and ilvD was downregulated, and the contents of (2S)-isopropylmalate and succinic acid decreased in M. metallidurans YC-39 under saline-alkali conditions, whereas B. siamensis BT-9-1 presented increased accumulation of these metabolites. These findings indicate that B. siamensis BT-9-1 cross-feeds M. metallidurans YC-39 with these metabolites, rescuing the compromised branched-chain amino acid synthesis pathway and the tricarboxylic acid cycle in saline-alkali environments. Eventually, coinoculation with B. siamensis BT-9-1 and M. metallidurans YC-39, along with (2S)-isopropylmalate and succinic acid supplementation, increased nitrogenase activity of the symbionts. Our study reveals a novel mechanism by which non-rhizobial endophyte Bacillus species enhances the growth and nitrogen fixation efficiency of M. metallidurans under saline-alkali stress through the delivery of key metabolites.
Phages infect bacteria by binding to specific surface receptors, driving co-evolution in microbial communities and offering therapeutic potential. However, how receptor specificity shapes the cross-resistance patterns and evolutionary trade-offs during phage-bacteria co-evolution remains unclear. Here, we investigated the genetic basis and fitness trade-offs of phage resistance in Salmonella to phages targeting O-antigen, core oligosaccharide, and BtuB (TonB-dependent receptor for vitamin B12) under individual or combinatorial pressures. The interaction matrices between phage-resistant strains and phages targeting three different receptors showed that bacterial cross-resistance to phages depends on the receptor type. Lipopolysaccharide (LPS) truncation conferred cross-resistance to phages targeting either the O-antigen or core oligosaccharide; whereas resistance to phages targeting BtuB occurred exclusively through mutations in the btuB gene. For LPS receptors whose biosynthesis involves multiple genes, the fitness cost associated with phage resistance is gene-specific. Among mutations conferring resistance to both O-antigen-targeting and core-targeting phages, those in the rfaJ gene exhibited the lowest fitness cost. The three-phage combination targeting three receptors exhibited potent antibacterial effects. Under this selective pressure, Salmonella developed resistance through receptor modification. Resistance to O-antigen-targeting and core-targeting phages emerged first through mutations in LPS biosynthesis genes, with mutations in the rfaJ gene dominating. Subsequently, mutations in the btuB gene accumulated to resist BtuB-targeting phages, ultimately evading predation by all three phages. Our results reveal receptor-driven evolutionary trade-offs and sequential resistance acquisition in Salmonella under multiple phages pressure, enhancing understanding of microbial interactions and informing phage therapy strategies.
A key bottleneck in microbiome engineering is ensuring long-term host association of introduced microbes. Selecting probiotic candidates based on evolutionary genomic decay signatures of emerging host dependency offers a potential solution. The Ruegeria strain B4 of population MC10, identified by such signatures, showed persistent coral colonization in a companion study. Whether this persistence translates into measurable host benefit compared to other coral-associated Ruegeria strains, and which mechanisms underlie such benefit, remained unknown. Here we directly compare the probiotic efficacy of MC10-B4 against two sympatric Ruegeria strains isolated from the same coral colony and mucus compartment, controlling for host genotype and microenvironment. MC10-B4 inoculation significantly increased heat stress tolerance in the model cnidarian Aiptasia (Exaiptasia diaphana strain H2), outperforming both controls. To understand the mechanistic basis, we characterized the functional profile of MC10-B4 using integrated multi-omics. The MC10 genome is enriched in host-interaction genes, including siderophore-mediated iron acquisition and exopolysaccharide biosynthesis, confirmed phenotypically by iron scavenging and enhanced biofilm formation. Following exposure to coral tissue extract, MC10-B4 underwent a coordinated "motile-to-sessile" proteomic reprogramming, downregulating flagellar motor components whereas upregulating flagellin and biofilm regulators. This response was distinct from sympatric relatives, which instead mounted broad upregulation of nutrient acquisition systems. MC10-B4's functional profile, particularly its oxidative stress sensitivity, contrasts with traits favored in conventional probiotic screens. Our results provide mechanistic insight into traits associated with long-term host association and thermal benefit, validating an evolution-guided approach that prioritizes innate colonization potential over pre-defined laboratory functionalities for rational probiotic design.
The squid-vibrio symbiosis has illuminated fundamental mechanisms of beneficial animal-microbe associations, yet the interactions within sepiolid squid of the Mediterranean Sea remain underexplored. Here, we characterize the Sepiola affinis squid-vibrio symbiosis by combining whole-genome sequencing of light-organ isolates, confocal microscopy, and temperature-dependent growth assays. Comparative genomic analyses (ANI, phylogenomics, and functional analyses) revealed two previously undescribed Vibrio species to be symbionts of the S. affinis light organ. One of the species clusters more distantly from other Vibrio species, whereas the second is closer to established Vibrio clades and exhibits an expanded repertoire of mobile elements and type VI secretion components, suggesting heightened capacity for genetic exchange and interbacterial interaction. Furthermore, confocal microscopy of juvenile squid established that the S. affinis light organ comprises twelve crypts connected by pores and ducts, expanding the number of symbiotic niches relative to other sepiolid squid. In addition, fluorescently labeled isolates from the two Vibrio species colonized juveniles in both mono- and co-colonization patterns within crypts. Finally, growth assays across 16°C-24°C identified species-specific temperature differences, indicating temperature preferences that may align with seasonal variability in the Mediterranean Sea. Together, these findings position S. affinis as a tractable model for studying how symbiont diversity, organ architecture, and interbacterial interactions contribute to the stability of a mutualistic symbiosis.
The plant pathogenic bacterium Clavibacter michiganensis (Cm) is a systemic vascular pathogen that colonizes both xylem vessels and the intracellular apoplast during different stages of infection. To identify traits and loci associated with adaptation to these distinct host microenvironments, we conducted tissue-specific experimental evolution. Twenty independent Cm lineages were repeatedly passaged in either tomato stems or leaves to promote adaptation to vascular or apoplastic lifestyles, respectively. After fifteen passages, adapted clones were characterized for virulence and virulence-related traits. These characterizations demonstrated clear differential associations of virulence-associated traits with the adapted tissue. The majority of vascular-adapted clones displayed enhanced surface attachment, reduced cellulase activity, reduced exopolysaccharide (EPS) production, and attenuated virulence on tomato compared to the parent clone. In contrast, apoplast-adapted clones displayed reduced biofilm formation and enhanced EPS production and retained their virulence on tomato. Whole-genome sequencing of all adapted clones revealed candidate loci linked to tissue adaptation. Six of ten vascular-adapted clones carried two independent mutations in CMM_1284, a putative HipB/XRE-type transcriptional regulator. A CMM_1284 marker exchange mutant displayed phenotypes similar to vascular-adapted clones, suggesting a role for this regulator in vascular colonization. Together, these findings highlight the role of phenotypic plasticity in tissue adaptation of plant pathogens, showing that tissue-specific adaptation involves modulation of surface attachment, EPS production, and cell wall-degrading enzymes and suggest a trade-off between vascular persistence, supported by strong surface attachment, and systemic virulence, which depends on bacterial dispersal and migration.
Microbial symbionts are closely related to the internal and external factors of their host. However, the prevalence of phylosymbiosis (the presence of host phylogenetic signal in microbial community composition) remains controversial, especially in animals collectively referred to as herpetofauna. To expand our understanding of host-microbiota interactions, we analysed 11 697 symbiotic microbiota samples from of 337 herpetofaunal species, covering skin, oral cavity, gut, cloaca, feces, and other body sites. The composition of the microbial communities gradually changes along the digestive tract, and is host-specific in each region. Overall, herpetofauna's dominant microbial taxa (Firmicutes, Proteobacteria, Bacteroidota) are more similar to mammals than fish (which are dominated by Proteobacteria, Firmicutes, and Fusobacteriota). However, phylosymbiosis in herpetofauna is weaker than in mammals and tends to occur at higher host taxonomic levels. The strength of the phylosymbiosis signal is influenced by body site, host genetic distance, and analytical method. It indicates that phylosymbiosis exists but is not universal. The intensity and significance of this signal are influenced by host taxonomic scale, the location of the microbial communities, and the assessment methods. These results advance our knowledge of host-microbe interactions across the Tree of Life.
Recognizing self-versus nonself is a crucial step in the development of multicellularity. The social bacterium Myxococcus xanthus is a tractable model organism for studying this transition from single-cell to multicellular life. The polymorphic cell-surface receptor TraA directs cooperative behaviors toward kin. TraA is a highly specific receptor, capable of recognizing other TraA proteins with identical or nearly identical sequences by homotypic binding, but the molecular basis of this specificity remains poorly understood. Here, we generated a targeted TraA mutant library comprising thousands of variants with substitutions at 10 predicted specificity-determining residues. Screening revealed variants with altered recognition profiles, often resulting in promiscuous and/or heterotypic TraA-TraA interactions. We further identified key residues that govern specificity, as substitutions at these positions rewired recognition outcomes. Finally, we propose an evolutionary model in which new TraA specificities arise through promiscuous intermediate states shaped by reward-punishment dynamics. Together, these findings demonstrate the malleability of TraA specificity and provide molecular and evolutionary insight into social recognition.