Vertebrate Gut Microbiota Research Articles

Location Matters: Variations in Cloacal Microbiota Composition of Spatially Separated Freshwater Turtles

The gut microbiota of vertebrates is malleable and may be shaped by both intrinsic and extrinsic factors. Here, the effect that geography has on the cloacal microbiota of two species of Australian freshwater chelonians, eastern longneck turtle (Chelodina longicollis) and Macquarie River turtle (Emydura macquarii), captured from waterbodies with different levels of anthropogenic pressure was investigated. We analysed the microbiota composition, structure and diversity through 16S rRNA gene amplicon sequencing. It was hypothesised that animals from less disturbed environments would harbour a more diverse cloacal microbial population. The cloacal microbiotas from 93 turtles (C. longicollis n = 78; E. macquarii n = 15), from five locations, were analysed. For both species, the most predominant phylum was Proteobacteria. Cloacal microbiota alpha diversity varied significantly between the C. longicollis from all locations, but no differences were found for E. macquarii. In C. longicollis, turtles from wetlands within the centre of Melbourne had the lowest alpha diversity metrics, while the highest alpha diversity values were seen in turtles captured from an undisturbed rural waterbody. Beta diversity, obtained by weighted UniFrac distance, showed significant differences between locations of capture for both species of turtles in this investigation. For C. longicollis, 87 biomarkers were identified responsible for explaining differences between locations, and in E. macquarii, 42 biomarkers were found. This is the first study to explore the cloacal microbiota composition of the eastern longneck turtle and gives greater insight into microbial community structures in Macquarie River turtles. Our study demonstrated that cloacal microbiota composition of freshwater turtles was significantly influenced by locality and that disrupted environments may reduce microbial diversity in C. longicollis. Interestingly, we discovered that the effects of location contrasted significantly between species for alpha diversity with differences discovered for C. longicollis but not E. macquarii. However, for both species, beta diversity was notably influenced by habitat type. These results highlight the need to interpret chelonian microbiota data in the context of geography and human disturbance of the environment.

Associations Between Gut Microbiota Diversity and a Host Fitness Proxy in a Naturalistic Experiment Using Threespine Stickleback Fish.

The vertebrate gut microbiota is a critical determinant of organismal function, yet whether and how gut microbial communities affect host fitness under natural conditions remains largely unclear. We characterised associations between a fitness proxy-individual growth rate-and bacterial gut microbiota diversity and composition in threespine stickleback fish introduced to large semi-natural ponds. We detected a 63% higher richness of bacterial taxa (α-diversity) in the guts of high-fitness fish compared to low-fitness fish, which might be driven by stronger bacterial dispersal among high-fitness fish according to the fit of a neutral community model. Further, microbial communities of high-fitness fish were more similar to one another (i.e., exhibited lower β-diversity) than those of low-fitness fish. The lower β-diversity found to be associated with higher host fitness is consistent with the Anna Karenina principle-that there are fewer ways to have a functional microbiota than a dysfunctional microbiota. Our study links differences in α- and β-diversity to a fitness-related trait in a vertebrate species reared under naturalistic conditions and our findings provide a basis for functional tests of the fitness consequences of host-microbiota interactions.

The strength of gut microbiota transfer along social networks and genealogical lineages in the house mouse.

The gut microbiota of vertebrates is acquired from the environment and other individuals, including parents and unrelated conspecifics. In the laboratory mouse, a key animal model, inter-individual interactions are severely limited and its gut microbiota is abnormal. Surprisingly, our understanding of how inter-individual transmission impacts house mouse gut microbiota is solely derived from laboratory experiments. We investigated the effects of inter-individual transmission on gut microbiota in two subspecies of house mice (Mus musculus musculus and M. m. domesticus) raised in a semi-natural environment without social or mating restrictions. We assessed the correlation between microbiota composition (16S rRNA profiles), social contact intensity (microtransponder-based social networks), and mouse relatedness (microsatellite-based pedigrees). Inter-individual transmission had a greater impact on the lower gut (colon and cecum) than on the small intestine (ileum). In the lower gut, relatedness and social contact independently influenced microbiota similarity. Despite female-biased parental care, both parents exerted a similar influence on their offspring's microbiota, diminishing with the offspring's age in adulthood. Inter-individual transmission was more pronounced in M. m. domesticus, a subspecies, with a social and reproductive network divided into more closed modules. This suggests that the transmission magnitude depends on the social and genetic structure of the studied population.

Structural and functional analyses of nematode-derived antimicrobial peptides support the occurrence of direct mechanisms of worm-microbiota interactions

The complex relationships between gastrointestinal (GI) nematodes and the host gut microbiota have been implicated in key aspects of helminth disease and infection outcomes. Nevertheless, the direct and indirect mechanisms governing these interactions are, thus far, largely unknown. In this proof-of-concept study, we demonstrate that the excretory-secretory products (ESPs) and extracellular vesicles (EVs) of key GI nematodes contain peptides that, when recombinantly expressed, exert antimicrobial activity in vitro against Bacillus subtilis. In particular, using time-lapse microfluidics microscopy, we demonstrate that exposure of B. subtilis to a recombinant saposin-domain containing peptide from the ‘brown stomach worm’, Teladorsagia circumcincta, and a metridin-like ShK toxin from the ‘barber’s pole worm’, Haemonchus contortus, results in cell lysis and significantly reduced growth rates. Data from this study support the hypothesis that GI nematodes may modulate the composition of the vertebrate gut microbiota directly via the secretion of antimicrobial peptides, and pave the way for future investigations aimed at deciphering the impact of such changes on the pathophysiology of GI helminth infection and disease.

Comparison of Surface Sterilization Methods for the Analysis of insect gut microbiota: Solenopsis invicta (Formicidae) as an example

The gut microbiota of vertebrates and invertebrates has become the focus of recent research. However, current sterilizing practices need more systematic quantitative methods due to limitations caused by their minute body size. Thus, an effective sterilization process incorporating organic and inorganic methods to obtain invertebrate microbiota, particularly when evaluating smaller insects, has yet to be elucidated. This study investigated if the whole abdomen should be utilized as the material to sterilize and examined whether physical and chemical surface sterilization methods could be combined to facilitate the acquisition of gut microbiota from theimported red fire ant (Solenopsis invicta Buren, 1972). Eight methods were designed by incorporating three chemical reagents (sterile water, 2.0 mg/L NaClO, and 75% ethanol) and one physical treatment (250 nm UV). The length range of the amplified fragment in the red imported fire ant is 401-450 bp. According to the results of the GLM regression model and interaction effect model, none of these factors (sterile water, 2.0 mg/L NaClO, and 75% ethanol, 250 nm UV) were significant for statistical regression of the Chao index, and these factors did not significantly interact with each other. Based on Alpha and Beta diversity analysis, none of the methods significantly affected the diversity of insects’ gut microbiome. Finally, we suggested that it is feasible for different species of small insects to select appropriate methods according to the current situation. Still, it is best to achieve unity in the same group.

Insights into early evolutionary adaptations of the Akkermansia genus to the vertebrate gut.

Akkermansia, a relevant mucin degrader from the vertebrate gut microbiota, is a member of the deeply branched Verrucomicrobiota, as well as the only known member of this phylum to be described as inhabitants of the gut. Only a few Akkermansia species have been officially described so far, although there is genomic evidence addressing the existence of more species-level variants for this genus. This niche specialization makes Akkermansia an interesting model for studying the evolution of microorganisms to their adaptation to the gastrointestinal tract environment, including which kind of functions were gained when the Akkermansia genus originated or how the evolutionary pressure functions over those genes. In order to gain more insight into Akkermansia adaptations to the gastrointestinal tract niche, we performed a phylogenomic analysis of 367 high-quality Akkermansia isolates and metagenome-assembled genomes, in addition to other members of Verrucomicrobiota. This work was focused on three aspects: the definition of Akkermansia genomic species clusters and the calculation and functional characterization of the pangenome for the most represented species; the evolutionary relationship between Akkermansia and their closest relatives from Verrucomicrobiota, defining the gene families which were gained or lost during the emergence of the last Akkermansia common ancestor (LAkkCA) and; the evaluation of the evolutionary pressure metrics for each relevant gene family of main Akkermansia species. This analysis found 25 Akkermansia genomic species clusters distributed in two main clades, divergent from their non-Akkermansia relatives. Pangenome analyses suggest that Akkermansia species have open pangenomes, and the gene gain/loss model indicates that genes associated with mucin degradation (both glycoside hydrolases and peptidases), (micro)aerobic metabolism, surface interaction, and adhesion were part of LAkkCA. Specifically, mucin degradation is a very ancestral innovation involved in the origin of Akkermansia. Horizontal gene transfer detection suggests that Akkermansia could receive genes mostly from unknown sources or from other Gram-negative gut bacteria. Evolutionary metrics suggest that Akkemansia species evolved differently, and even some conserved genes suffered different evolutionary pressures among clades. These results suggest a complex evolutionary landscape of the genus and indicate that mucin degradation could be an essential feature in Akkermansia evolution as a symbiotic species.

Phylogenetic comparative approach reveals evolutionary conservatism, ancestral composition, and integration of vertebrate gut microbiota.

How host-associated microbial communities evolve as their hosts diversify remains equivocal: How conserved is their composition? What was the composition of ancestral microbiota? Do microbial taxa covary in abundance over millions of years? Multivariate phylogenetic models of trait evolution are key to answering similar questions for complex host phenotypes, yet they are not directly applicable to relative abundances, which usually characterize microbiota. Here, we extend these models in this context, thereby providing a powerful approach for estimating phylosymbiosis (the extent to which closely related host species harbor similar microbiota), ancestral microbiota composition, and integration (evolutionary covariations in bacterial abundances). We apply our model to the gut microbiota of mammals and birds. We find significant phylosymbiosis that is not entirely explained by diet and geographic location, indicating that other evolutionary-conserved traits shape microbiota composition. We identify main shifts in microbiota composition during the evolution of the two groups and infer an ancestral mammalian microbiota consistent with an insectivorous diet. We also find remarkably consistent evolutionary covariations among bacterial orders in mammals and birds. Surprisingly, despite the substantial variability of present-day gut microbiota, some aspects of their composition are conserved over millions of years of host evolutionary history.

Comparative analysis of two nonlethal methods for the study of the gut bacterial communities in wild lizards.

Fecal samples or cloacal swabs are preferred over lethal dissections to study vertebrate gut microbiota for ethical reasons, but it remains unclear which nonlethal methods provide more accurate information about gut microbiota. We compared the bacterial communities of three gastrointestinal tract (GIT) segments, that is, stomach, small intestine (midgut), and rectum (hindgut) with the bacterial communities of the cloaca and feces in the mesquite lizard Sceloporus grammicus. The hindgut had the highest taxonomic and functional alpha diversity, followed by midgut and feces, whereas the stomach and cloaca showed the lowest diversities. The taxonomic assemblages of the GIT segments at the phylum level were strongly correlated with those retrieved from feces and cloacal swabs (rs > 0.84 in all cases). The turnover ratio of Amplicon Sequence Variants (ASVs) between midgut and hindgut and the feces was lower than the ratio between these segments and the cloaca. More than half of the core-ASVs in the midgut (24 of 32) and hindgut (58 of 97) were also found in feces, while less than 5 were found in the cloaca. At the ASVs level, however, the structure of the bacterial communities of the midgut and hindgut were similar to those detected in feces and cloaca. Our findings suggest that fecal samples and cloacal swabs of spiny lizards provide a good approximation of the taxonomic assemblages and beta diversity of midgut and hindgut microbiota, while feces better represent the bacterial communities of the intestinal segments at a single nucleotide variation level than cloacal swabs.

Gut microbiota of two invasive fishes respond differently to temperature.

Temperature variation structures the composition and diversity of gut microbiomes in ectothermic animals, key regulators of host physiology, with potential benefit to host or lead to converse results (i.e., negative). So, the significance of either effect may largely depend on the length of time exposed to extreme temperatures and how rapidly the gut microbiota can be altered by change in temperature. However, the temporal effects of temperature on gut microbiota have rarely been clarified. To understand this issue, we exposed two juvenile fishes (Cyprinus carpio and Micropterus salmoides), which both ranked among the 100 worst invasive alien species in the world, to increased environmental temperature and sampled of the gut microbiota at multiple time points after exposure so as to determine when differences in these communities become detectable. Further, how temperature affects the composition and function of microbiota was examined by comparing predicted metagenomic profiles of gut microbiota between treatment groups at the final time point of the experiment. The gut microbiota of C. carpio was more plastic than those of M. salmoides. Specifically, communities of C. carpio were greatly altered by increased temperature within 1 week, while communities of M. salmoides exhibit no significant changes. Further, we identified 10 predicted bacterial functional pathways in C. carpio that were temperature-dependent, while none functional pathways in M. salmoides was found to be temperature-dependent. Thus, the gut microbiota of C. carpio was more sensitive to temperature changes and their functional pathways were significantly changed after temperature treatment. These results showed the gut microbiota of the two invasive fishes differ in response to temperature change, which may indicate that they differ in colonization modes. Broadly, we have confirmed that the increased short-term fluctuations in temperatures are always expected to alter the gut microbiota of ectothermic vertebrates when facing global climate change.

Longitudinal analysis of changes in the gut microbiota of zebrafish following acute spring viremia of carp virus infection

The gut microbiota of vertebrates plays a critical role in resistance to invading pathogens. Spring viremia of carp (SVC) is one of the most severe viral diseases in aquaculture. The causative agent is the SVC virus (SVCV), resulting in devastating damage to cyprinid. Yet, knowledge regarding the relationship between the gut microbes and disease is still lacking, particularly the dynamic alteration of the gut microbiota in fish following SVCV infection. To understand the longitudinal effects of SVCV infection on the microbiota of the zebrafish intestine, an intraperitoneal injection zebrafish model mimicking acute SVCV infection in fish with typical virologic and pathologic features was used. Intestinal microbes from both control (CON) and SVCV-infected fish were characterized at various time points by 16S ribosomal RNA gene V3-V4 region sequencing. Viral load in spleen, kidney, and intestine and the total bacterial load in the gut were detected by qPCR.The results showed that SVCV infection was associated with alterations of the gut microbiota in zebrafish as indicated by both alpha and beta diversity indexes. Compared with the CON group, SVCV-infected fish had significantly reduced bacterial diversity at 4 to 6 days post-infection (dpi). It has been found that a number of bacteria were enriched in opportunistic pathogens and depleted of beneficial commensals, at the time of onset of obvious symptoms or even death and at the time of complete disappearance of symptoms. A noticeably higher relative abundance of opportunistic pathogens, such as Clostridium_XlVa, Vibrio, Aeromonas, Mycoplasmataceae_unclassified, and Rothia; and a lower relative abundance of beneficial symbionts were found in the gut microbiome at 4, 7, 10 days post-infection. Five biomarkers showed high accuracy for distinguishing SVCV-infected fish from CON with an area under the curve (AUC) up to 0.78, 0.80, 0.79, 0.89, and 0.84, respectively. The relative abundance of Enterobacteriaceae_unclassified showed a positive correlation with viral loads of SVCV and the relative abundance of Cetobacterium and Aeromonas were positively related to the bacterial load in the gut, while the same results were observed for the corresponding two phyla (Fusobacteria and Proteobacteria). SVCV causes long-term gut microbiome dysbiosis, which is linked to viral load in target organs and total intestinal bacterial count. The results of our study suggest the potential value of the gut microbiota as a diagnostic biomarker and therapeutic target for SVC, but further validation is required.

Host Species Adaptation of Obligate Gut Anaerobes Is Dependent on Their Environmental Survival.

The gut microbiota of warm-blooded vertebrates consists of bacterial species belonging to two main phyla; Firmicutes and Bacteroidetes. However, does it mean that the same bacterial species are found in humans and chickens? Here we show that the ability to survive in an aerobic environment is central for host species adaptation. Known bacterial species commonly found in humans, pigs, chickens and Antarctic gentoo penguins are those capable of extended survival under aerobic conditions, i.e., either spore-forming, aerotolerant or facultatively anaerobic bacteria. Such bacteria are ubiquitously distributed in the environment, which acts as the source of infection with similar probability in humans, pigs, chickens, penguins and likely any other warm-blooded omnivorous hosts. On the other hand, gut anaerobes with no specific adaptation for survival in an aerobic environment exhibit host adaptation. This is associated with their vertical transmission from mothers to offspring and long-term colonisation after administration of a single dose. This knowledge influences the design of next-generation probiotics. The origin of aerotolerant or spore-forming probiotic strains may not be that important. On the other hand, if Bacteroidetes and other host-adapted species are used as future probiotics, host preference should be considered.

Diversity and compositional changes in the gut microbiota of wild and captive vertebrates: a meta-analysis

The gut microbiota is recognised as an essential asset for the normal functioning of animal biology. When wild animals are moved into captivity, the modified environmental pressures are expected to rewire the gut microbiota, yet whether this transition follows similar patterns across vertebrates is still unresolved due to the absence of systematic multi-species analyses. We performed a meta-analysis of gut microbiota profiles of 322 captive and 322 wild specimens from 24 vertebrate species. Our analyses yielded no overall pattern of diversity and compositional variation between wild and captive vertebrates, but a heterogeneous landscape of responses, which differed depending on the components of diversity considered. Captive populations showed enrichment patterns of human-associated microorganisms, and the minimal host phylogenetic signal suggests that changes between wild and captive populations are mainly driven by case-specific captivity conditions. Finally, we show that microbiota differences between wild and captive populations can impact evolutionary and ecological inferences that rely on hierarchical clustering-based comparative analyses of gut microbial communities across species.

Context-dependent effects of glucocorticoids on the lizard gut microbiome.

The vertebrate gut microbiota (bacterial, archaeal and fungal communities of the gastrointestinal tract) can have profound effects on the physiological processes of their hosts. Although relatively stable, changes in microbiome structure and composition occur due to changes in the environment, including exposure to stressors and associated increases in glucocorticoid hormones. Although a growing number of studies have linked stressor exposure to microbiome changes, few studies have experimentally explored the specific influence of glucocorticoids on the microbiome in wild animals, or across ecologically important processes (e.g., reproductive stages). Here we tested the response of the gut microbiota of adult female Sceloporus undulatus across gestation to ecologically relevant elevations of a stress-relevant glucocorticoid hormone (CORT) in order to determine (i) how experimentally elevated CORT influenced microbiome characteristics, and (ii) whether this relationship was dependent on reproductive context (i.e., whether females were gravid or not, and, in those that were gravid, gestational stage). We show that the effects of CORT on gut microbiota are complex and depend on both gestational state and stage. CORT treatment altered microbial community membership and resulted in an increase in microbiome diversity in late-gestation females, and microbial community membership varied according to treatment. In nongravid females, CORT treatment decreased interindividual variation in microbial communities, but this effect was not observed in late-gestation females. Our results highlight the need for a more holistic understanding of the downstream physiological effects of glucocorticoids, as well as the importance of context (here, gestational state and stage) in interpreting stress effects in ecology.

Culture-enriched community profiling improves resolution of the vertebrate gut microbiota.

Vertebrates harbour gut microbial communities containing hundreds of bacterial species, most of which have never been cultivated or isolated in the laboratory. The lack of cultured representatives from vertebrate gut microbiotas limits the description and experimental interrogation of these communities. Here, we show that representatives from >50% of the bacterial genera detected by culture-independent sequencing in the gut microbiotas of fence lizards, house mice, chimpanzees, and humans were recovered in mixed cultures from frozen faecal samples plated on a panel of nine media under a single growth condition. In addition, culturing captured >100 rare bacterial genera overlooked by culture-independent sequencing, more than doubling the total number of bacterial sequence variants detected. Our approach recovered representatives from 23 previously uncultured candidate bacterial genera, 12 of which were not detected by culture-independent sequencing. Results identified strategies for both indiscriminate and selective culturing of the gut microbiota that were reproducible across vertebrate species. Isolation followed by whole-genome sequencing of 161 bacterial colonies from wild chimpanzees enabled the discovery of candidate novel species closely related to the opportunistic pathogens of humans Clostridium difficile and Hungatella hathewayi. This study establishes culturing methods that improve inventories and facilitate isolation of gut microbiota constituents from a wide diversity of vertebrate species.

Two hundred and fifty-four metagenome-assembled bacterial genomes from the bank vole gut microbiota

Vertebrate gut microbiota provide many essential services to their host. To better understand the diversity of such services provided by gut microbiota in wild rodents, we assembled metagenome shotgun sequence data from a small mammal, the bank vole Myodes glareolus (Rodentia, Cricetidae). We were able to identify 254 metagenome assembled genomes (MAGs) that were at least 50% (n = 133 MAGs), 80% (n = 77 MAGs) or 95% (n = 44 MAGs) complete. As typical for a rodent gut microbiota, these MAGs are dominated by taxa assigned to the phyla Bacteroidetes (n = 132 MAGs) and Firmicutes (n = 80), with some Spirochaetes (n = 15) and Proteobacteria (n = 11). Based on coverage over contigs, Bacteroidetes were estimated to be most abundant group, followed by Firmicutes, Spirochaetes and Proteobacteria. These draft bacterial genomes can be used freely to determine the likely functions of gut microbiota community composition in wild rodents.

Individual and Site-Specific Variation in a Biogeographical Profile of the Coyote Gastrointestinal Microbiota.

Most knowledge of the vertebrate gut microbiota comes from fecal samples; due to difficulties involved in sample collection, the upper intestinal microbiota is poorly understood in wild animals despite its potential to inform broad interpretations about host-gut microbe relationships under natural conditions. Here, we used 16S rRNA gene sequencing to characterize the microbiota of wild coyotes (Canis latrans) along the gastrointestinal tract, including samples from the duodenum, jejunum, ileum, caecum, ascending and descending colon, and feces. We used this intestinal profile to (1) quantify how intestinal site and individual identity interact to shape the microbiota in an uncontrolled setting, and (2) evaluate whether the fecal microbiota adequately represent other intestinal sites. Microbial communities in the large intestine were distinct from those in the small intestine, with higher diversity and a greater abundance of anaerobic taxa. Within each of the small and large intestine, individual identity explained significantly more among-sample variation than specific intestinal sites, revealing the importance of individual variation in the microbiota of free-living animals. Fecal samples were not an adequate proxy for studying upper intestinal environments, as they contained only half the amplicon sequence variants (ASVs) present in the small intestine at three- to four-fold higher abundances. Our study is a unique biogeographical investigation of the microbiota using free-living mammals rather than livestock or laboratory organisms and provides a foundational understanding of the gastrointestinal microbiota in a wild canid.

Gut microbiota of invasive bullfrog tadpoles responds more rapidly to temperature than a noninvasive congener

Environmental temperature can alter the composition, diversity, and function of ectothermic vertebrate gut microbial communities, which may result in negative consequences for host physiology, or conversely, increase phenotypic plasticity and persistence in harsh conditions. The magnitude of either of these effects will depend on the length of time animals are exposed to extreme temperatures, and how quickly the composition and function of the gut microbiota can respond to temperature change. However, the temporal effects of temperature on gut microbiota are currently unknown. Here, we investigated the length of time required for increased temperature to alter the composition of gut bacterial communities in tadpoles of two frog species, the green frog, Lithobates clamitans, and its congener, the globally invasive American bullfrog, L.catesbeianus. We also explored the potential functional consequences of these changes by comparing predicted metagenomic profiles across temperature treatments at the last experimental time point. Bullfrog-associated microbial communities were more plastic than those of the green frog. Specifically, bullfrog communities were altered by increased temperature within hours, while green frog communities took multiple days to exhibit significant changes. Further, over ten times more bullfrog bacterial functional pathways were temperature-dependent compared to the green frog. These results support our hypothesis that bullfrog gut microbial communities would respond more rapidly to temperature change, potentially bolstering their ability to exploit novel environments. More broadly, we have revealed that even short-term increases in environmental temperature, expected to occur frequently under global climate change, can alter the gut microbiota of ectothermic vertebrates.

The gut microbiota response to helminth infection depends on host sex and genotype.

Vertebrates' gut microbial communities can be altered by the hosts' parasites. Helminths inhabiting the gut lumen can interact directly with their host's microbiota via physical contact, chemical products, or competition for nutrients. Indirect interactions can also occur, for instance when helminths induce or suppress host immunity in ways that have collateral effects on the microbiota. If there is genetic variation in host immune responses to parasites, we would expect such indirect effects to be conditional on host genotype. To test for such genotype by infection interactions, we experimentally exposed Gasterosteus aculeatus to their naturally co-evolved parasite, Schistocephalus solidus. The host microbiota differed in response to parasite exposure, and between infected and uninfected fish. The magnitude and direction of microbial responses to infection differed between host sexes, and also differed between variants at autosomal quantitative trait loci. These results indicate that host genotype and sex regulate the effect of helminth infection on a vertebrate gut microbiota. If this result holds in other taxa, especially humans, then helminth-based therapeutics for dysbiosis might need to be tailored to host genotype and sex.

Distinct microbiotas of anatomical gut regions display idiosyncratic seasonal variation in an avian folivore

BackgroundCurrent knowledge about seasonal variation in the gut microbiota of vertebrates is limited to a few studies based on mammalian fecal samples. Seasonal changes in the microbiotas of functionally distinct gut regions remain unexplored. We investigated seasonal variation (summer versus winter) and regionalization of the microbiotas of the crop, ventriculus, duodenum, cecum, and colon of the greater sage-grouse (Centrocercus urophasianus), an avian folivore specialized on the toxic foliage of sagebrush (Artemesia spp.) in western North America.ResultsWe sequenced the V4 region of the 16S rRNA gene on an Illumina MiSeq and obtained 6,639,051 sequences with a median of 50,232 per sample. These sequences were assigned to 457 bacterial and 4 archaeal OTUs. Firmicutes (53.0%), Bacteroidetes (15.2%), Actinobacteria (10.7%), and Proteobacteria (10.1%)were the most abundant and diverse phyla. Microbial composition and richness showed significant differences among gut regions and between summer and winter. Gut region explained almost an order of magnitude more variance in our dataset than did season or the gut region × season interaction. The effect of season was uneven among gut regions. Microbiotas of the crop and cecum showed the greatest seasonal differences.ConclusionsOur data suggest that seasonal differences in gut microbiota reflect seasonal variation in the microbial communities associated with food and water. Strong differentiation and uneven seasonal changes in the composition and richness of the microbiota among functionally distinct gut regions demonstrate the necessity of wider anatomical sampling for studies of composition and dynamics of the gut microbiota.

Significant Differences in Bacterial and Potentially Pathogenic Communities Between Sympatric Hooded Crane and Greater White-Fronted Goose.

The gut microbiota of vertebrates play a crucial role in shaping the health of their hosts. However, knowledge of the avian intestinal microbiota has arguably lagged behind that of many other vertebrates. Here, we examine the intestinal bacterial communities of the hooded crane and the greater white-fronted goose at the Shengjin Lake of China, using high-throughput sequencing (Illumina Mi-Seq), and infer the potential pathogens associated with each species. Intestinal bacterial alpha-diversity in the greater white-fronted goose was significantly higher than that in hooded crane. The intestinal bacterial community compositions were significantly different between the two hosts, suggesting that host interactions with specific communities might have profound implications. In addition, potential pathogens were detected in both guts of the two hosts, suggesting that these wild birds might be at risk of disease and probably spread infectious disease to other sympatric vertebrates. The gut of hooded crane carried more potential pathogens than that of the greater white-fronted goose. The potentially pathogenic community compositions were also significantly different between the two hosts, suggesting the divergence of potentially pathogenic communities between hooded crane, and greater white-fronted goose. Finally, bacterial and potentially pathogenic structures showed strong evidence of phylogenic clustering in both hosts, further demonstrating that each host was associated with preferential and defined bacterial and potentially pathogenic communities. Our results argue that more attention should be paid to investigate avian intestinal pathogens which might increase disease risks for conspecifics and other mixed species, and even poultry and human beings.