Toll-like receptor 2 (TLR2) plays a pivotal role in innate immunity and has recently emerged as a critical regulator of host-microbiome interactions. However, how TLR2 influences host transcriptional responses to colonized microbiome and microbial community dynamics remains largely unclear. A comparison between germ free (GF) and conventionalized zebrafish (Danio rerio) larvae provides a valuable system to investigate how the microbiome influences host transcriptomic responses in a tlr2 mutant versus wild-type control. Vice versa, to understand the role of Tlr2 in regulating the microbiome, we have analyzed microbial community composition in both tlr2 mutant and wild-type zebrafish at larval and adult stages. RNAseq analysis revealed that approximately 2.6% of the zebrafish genome (827 genes) exhibited transcriptomic alterations in tlr2 mutant larvae compared to the wild type under microbiome-colonized conditions, whereas around 2% of the genome (639 genes) showed differential expression under GF conditions. KEGG enrichment analyses show that under both microbiome-colonized and GF conditions major differences between the tlr2 mutant and wild type are related to metabolism. Furthermore, there is a striking difference in endoplasmic reticulum stress responses, including well-known markers for inflammatory bowel disease which are all downregulated in the mutant under the microbiome-colonized condition. Microbiome colonization elicited a broader transcriptional response in tlr2 wild-type larvae than in the mutant, with specifically the ferroptosis, apoptosis and inflammation related pathways differently regulated. In terms of how Tlr2 influences microbial composition, 16 S rRNA gene sequencing showed large differences in beta diversity between the tlr2 mutant and wild type. The tlr2 mutant exhibited higher microbial alpha diversity during early development, whereas alpha diversity was higher in wild-type adults. For larvae at the genus level, tlr2 mutant larvae showed increased Chryseobacterium and Flectobacillus but reduced Gracilibacteria abundance relative to wild-type controls. For adult gut samples, the relative abundance of Cetobacterium was higher in the tlr2 mutants, indicating a developmental stage-specific restructuring of the microbiome. TLR2 not only modulates host transcriptional responses to microbial colonization, but also shapes gut microbial diversity, composition, and metabolic potential. Our findings highlight the critical role of TLR2 in orchestrating immune-metabolic homeostasis and provide new insights into its broader function in maintaining host-microbiota symbiosis across developmental stages.

We investigated the early-life interplay between microbiota, host, and environment by longitudinally monitoring nasal and gut microbiota in 30 veal calves over their first five months of life. Microbial composition and stability were highly compartmentalized. Fecal communities showed increasing biomass, diversity, and homogeneity with age. Conversely, nasal microbiota remained less diverse and highly variable between individuals, likely influenced by mucociliary clearance and transient colonization. Environmental factors, diet, and clinical indicators were associated with both microbial communities, alongside distinct cytokine profiles. As calves matured, microbiota dynamics and composition covaried across body sites, reflecting systemic immune development and environmental adaptations. This study provides a comprehensive, multi-layered characterization of microbial dynamics, identifying the first month of life as a critical window for interventions targeting the fecal microbiota. The nasal microbiota, by contrast, remains flexible and amenable to modulation throughout the production cycle.Supplementary InformationThe online version contains supplementary material available at 10.1186/s42523-025-00494-w.

Mosquito microbiota abundance and composition are modulated by a variety of factors, including pathogen exposure. The microbiome can also influence pathogen infection of the host and thus harbours considerable potential to impact transmission of pathogens. As such, there is a growing interest in using particular bacterial members of the microbiota for novel vector-control strategies. However, before novel microbiota-based approaches can move towards translation, a more complete understanding of the interactions between mosquitoes, their microbiome, and the pathogens they transmit, is required to better appreciate how variation in the microbiome of field mosquitoes affects these interactions. To examine the impact of the mosquito background and the associated diversity of bacterial microbiota within distinct hosts, we exposed several laboratory-reared and field-collected Aedes aegypti mosquito lines to Zika virus (ZIKV) and examined their bacterial load and composition in response to pathogen exposure and viral infection success. Intriguingly, we show that ZIKV exposure and infection had distinct impacts on microbiome composition and density within different mosquito lines. In one laboratory-reared line ZIKV exposure and infection reduced the bacterial load, while conversely in another line load was increased by the virus. Distinct responses of the microbiome were also seen in mosquitoes collected from the field. Sampling site-specific differences in the microbiome of mosquitoes were observed as virus infection altered microbiome alpha and beta diversities in one cohort, while in mosquitoes from other sampling sites, viral progression through the mosquito had minimal effect on the microbiome. We also identified bacterial taxa correlating with either ZIKV infection or a lack of infection. These taxa are potential candidates for future follow-up studies disentangling functional mechanisms and directionality of interactions. Overall, our study highlights that interactions between mosquito, virus, and microbiota are variable and context dependent, and that tripartite interactions among distinct mosquito cohorts and their microbiomes are not universal.

BackgroundArtificial diet-reared silkworms (Bombyx mori) exhibit reduced gut microbial diversity and impaired growth performance compared to mulberry-fed counterparts. While Bacillus subtilis is widely used as a probiotic in livestock and aquaculture, its impact on silkworms remains unexplored. This study investigates whether dietary supplementation with B. subtilis enhances larval development and elucidates the underlying mechanisms involving gut microbiota and metabolic pathways.ResultsSupplementing artificial diets with B. subtilis (6 × 105 CFU/g) significantly increased larval body weight by 9.1–22.1% during instar stages and improved feed utilization efficiency (FUE) by 4.09%–6.80% compared to controls. Cocoon quality metrics, including cocoon shell weight (+ 9.77% in females) and cocoon shell ratio (+ 6.56%), also improved. Mechanistically, B. subtilis did not colonize the midgut but transiently modulated gut physiology: it elevated midgut fluid pH and enhanced α-amylase, trypsin, and lipase activities. 16 S rRNA sequencing revealed reduced gut microbial diversity (Shannon index, P < 0.01) and shifts in community structure, with decreased abundances of potential pathogens (e.g., Pseudomonas) and commensals (e.g., Lactobacillus). Targeted metabolomics identified a 3.1-fold increase in phenylalanine levels in hemolymph, linked to upregulated aromatic amino acid metabolism pathways (KEGG). Dietary phenylalanine supplementation (0.4%) replicated B. subtilis-induced growth promotion, confirming its pivotal role in host-microbe interactions.ConclusionsB. subtilis enhances silkworm growth and silk production through multi-faceted mechanisms: reshaping gut microbiota composition, improving digestive enzyme activity, and elevating phenylalanine biosynthesis. These findings establish B. subtilis as a promising probiotic for optimizing artificial diet systems in Lepidoptera and highlight the central role of amino acid metabolism in insect-microbiome symbiosis.Supplementary InformationThe online version contains supplementary material available at 10.1186/s42523-025-00473-1.

The bacterial genus Endozoicomonas is a predominant member of the coral microbiome, widely recognised for its ubiquity and ability to form high-density aggregates within coral tissues. Hence, investigating its metabolic interplay with coral hosts offers critical insights into its ecological roles and contributions to coral health and resilience. Using long- and short-read whole-genome sequencing of 11 Endozoicomonas strains from Acropora loripes, genome sizes were found to range between 5.8 and 7.1 Mbp. Phylogenomic analysis identified two distinct clades within the family Endozoicomonadaceae. Metabolic reconstruction uncovered clade-specific pathways, including the degradation of holobiont-derived carbon and lipids (e.g., galactose, starch, triacylglycerol, D-glucuronate), the latter of which suggests involvement of Endozoicomonas in host 'sex-type' steroid hormone metabolism. A clade-specific type 6 Secretion System (T6SS) and predicted effector molecules were identified, potentially facilitating coral-bacterium symbiosis. Additionally, genomic analyses revealed diverse phosphorus acquisition strategies, implicating Endozoicomonas in holobiont phosphorus cycling and stress responses. This study reveals clade-specific genomic signatures of Endozoicomonas supporting its mutualistic lifestyle within corals. Findings suggests possible roles in nutrient cycling, reproductive health, and stress resilience, offering novel insights into coral holobiont functioning.

Metronidazole is a potent antibiotic often prescribed to treat gastrointestinal enteropathies, but is known to induce loose stools, negatively alter the fecal microbiome, and affect fecal metabolites. Dietary intervention may aid in the recovery following antibiotic cessation, but little research has been conducted regarding the potential of fiber utilization for microbial recovery in canines. Using an in vitro fermentation assay, the objective of this study was to investigate the fermentation characteristics of dietary fibers using fecal inocula from dogs treated with metronidazole. Four healthy male beagles were fed a commercial kibble diet for 2 weeks, then administered metronidazole (20 mg/kg body weight twice a day) for 2 weeks. Fresh fecal samples were collected at weeks 2 and 4, stabilized in a 20% glycerol solution, and then frozen. For the in vitro fermentation experiment, feces from each time point (ABX−= pre-metronidazole collection; ABX+ = post-metronidazole collection) were thawed, diluted in an anaerobic diluting solution, and used to inoculate tubes. Tubes contained sterile medium and either cellulose, pectin, beet pulp, or chicory pulp fiber to test fermentation potential, with additional tubes used without fiber inclusion for blank corrections. At baseline (0 h) and after 6, 12, and 18 h of fermentation, pH, short-chain fatty acid (SCFA) production, and microbiota were measured. Data was analyzed within each fiber using the Mixed Models procedure of SAS version 9.4, with effects of antibiotic treatment, time and treatment*time interactions reported, accounting for the random effect across replicates. As expected, antibiotic administration had large effects on fiber fermentability characteristics, slowing pH reduction, lowering SCFA production, and altering SCFA molar ratios. Butyrate production was minimal among all fibers tested in ABX+ inocula tubes. Additionally, ABX+ inoculum lowered bacterial alpha diversity, affected bacterial beta diversity and the relative abundances of over 50 bacterial genera. Increased Bifidobacterium and Lactobacillus was observed in tubes containing ABX + inoculum (P < 0.0001) during pectin or beet pulp fermentation. Additionally, increased Faecalibacterium, Streptococcus, and Bacteroides was observed in tubes containing ABX- inoculum during chicory pulp fermentation (P < 0.0001). Beta diversity plots during beet pulp and chicory pulp fermentation demonstrated positive shifts toward ABX- inoculum tubes, but pectin fermentation did not yield the same shifts. The data presented here demonstrate that metronidazole administration can elicit unique responses to various fiber sources by reducing microbial diversity and negatively altering microbial fermentative activity (i.e., lower SCFA production). Both beet pulp and chicory pulp increased SCFA production and microbial diversity over time, with ABX+ inoculum tubes approaching that of ABX- inoculum tubes after 18 h of fermentation. More research is necessary but this data suggests that functional fibers promote microbial activity and recovery, and shed light on the potential effects of functional fibers in antibiotic-treated dogs.Supplementary InformationThe online version contains supplementary material available at 10.1186/s42523-025-00459-z.

Gut microbiomes play critical roles in host-environment interactions, reflecting habitat and foraging niches. North American bison (Bison bison) subspecies—plains bison (B. bison bison) and wood bison (B. bison athabascae)—exhibit limited genetic variation from historic population bottleneck events, potentially undermining their evolutionary potential. Understanding variation in gut microbiota composition between subspecies may shed light on genetic, phenotypic, and ecological divergence relevant to their adaptive capacities. Using 16S rRNA metabarcoding of fecal samples, we characterized the gut microbiota of both subspecies in the sympatric environment of Elk Island National Park, providing insight into potential phylogenetic gut microbiome divergence. Like other ruminants, the gut microbial community of both subspecies consists primarily of the bacterial phyla Firmicutes and Bacteroidetes. Subspecific classification explained no significant differences in alpha diversity (p > 0.05) in the overall dataset, but has a potentially significant effect on beta diversity (p < 0.05, R2 = 0.04). Gut microbiota divergence between subspecies may be driven by differential abundance of specific taxa and associated functional pathways, likely influenced by dietary preferences, ancestral phenotypes, and historical ranges. Our findings support further investigation into diet-microbiome relationships between subspecies in sympatric environments and metagenomic approaches to explore functional differences in the gut microbiome.

The combination of meglumine antimoniate and allopurinol is considered one of the most effective treatments for canine leishmaniosis caused by Leishmania infantum. This study investigated the effects of this treatment on the gut microbiome of 10 dogs from Spain, Portugal, and Italy via fecal shotgun metagenomic sequencing over six months. Dogs were sampled at baseline (BL), after one month of combined treatment with meglumine antimoniate and allopurinol (M1) and after six months of allopurinol treatment (M6). Fecal samples had their total DNA extracted and sequenced by Illumina sequencing. Posteriorly, a microbiome analysis was conducted to analyze bacterial abundance, diversity and enrichment. The gut microbiome of Leishmania-infected dogs (BL) is dominated by Prevotella, Collinsella, Bacteroides, and Blautia, with individual variability being the primary determinant of microbiome composition. No significant changes in alpha diversity (Shannon index, gene number) or beta diversity (Bray-Curtis dissimilarity, UniFrac distance) were detected between pre- and post-treatment time points, suggesting that treatment with meglumine antimoniate and allopurinol does not disrupt the gut microbiota. Minor trends in taxonomic shifts were noted, with slight increases in Bifidobacterium pseudocantenulatum, Collinsella tanakaei, and Slackia piriformis after treatment, but these changes were not statistically significant after correction for multiple testing. Linear discriminant analysis and multivariable modeling confirmed that the microbial community structure was resilient to treatment effects. Individual-specific microbiome differences in diversity accounted for 52% of the observed variability, underscoring the personalized nature of the gut microbiota in dogs. Importantly, no adverse microbiome disruptions were detected, even with prolonged allopurinol use. This study highlights the robustness of the canine gut microbiome during antileishmanial therapy and highlights the use of meglumine antimoniate and allopurinol without compromising gut microbial diversity or health. Further studies with larger cohorts are recommended to confirm these findings and explore the functional roles of the gut microbiota in modulating immune responses in Leishmania-infected dogs.