Effects of Paraquat, Dextran Sulfate Sodium, and Irradiation on Behavioral and Cognitive Performance and the Gut Microbiome in A53T and A53T-L444P Mice.

Heterozygous carriers of the glucocerebrosidase 1 (GBA) L444P Gaucher mutation have an increased risk of developing Parkinson's disease (PD). The GBA mutations result in elevated alpha synuclein (aSyn) levels. Heterozygous mice carrying one allele with the L444P mutation knocked-into the mouse gene show increased aSyn levels and are more sensitive to motor deficits following exposure to the neurotoxin (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) MPTP than wild-type mice. Paraquat (PQ), a herbicide, increases PD risk in most studies. Its effects on the brain involve alterations in the gut microbiome. Exposure to dextran sulfate sodium (DSS), a mouse model of colitis, can be used to determine whether gut microbiome alterations are sufficient to induce PD-relevant phenotypes. We rederived the A53T-L444P and A53T mouse lines to assess whether PQ, PQ in combination with radiation exposure (IR), and DSS have differential effects in A53T and A53T-L444P mice and whether these effects are associated with alterations in the gut microbiome. PQ and PQ + IR have differential effects in A53T and A53T-L444P mice. In contrast, effects of DSS are only seen in A53T-L444P mice. Exposure and genotype modulate the relationship between the gut microbiome and behavioral performance. The gut microbiome may be an important mediator of how environmental exposures or genetic mutations yield behavioral and cognitive impacts.

Association between Gut Microbiota and Breast Cancer: Diet as a Potential Modulating Factor.

Breast cancer (BCa) has many well-known risk factors, including age, genetics, lifestyle, and diet; however, the influence of the gut microbiome on BCa remains an emerging area of investigation. This study explores the connection between the gut microbiome, dietary habits, and BCa risk. We enrolled newly diagnosed BCa patients and age-matched cancer-free controls in a case-control study. Comprehensive patient data was collected, including dietary habits assessed through the National Cancer Institute Diet History Questionnaire (DHQ). 16S rRNA amplicon sequencing was used to analyze gut microbiome composition and assess alpha and beta diversity. Microbiome analysis revealed differences in the gut microbiome composition between cases and controls, with reduced microbial diversity in BCa patients. The abundance of three specific microbial genera-Acidaminococus, Tyzzerella, and Hungatella-was enriched in the fecal samples taken from BCa patients. These genera were associated with distinct dietary patterns, revealing significant associations between the presence of these genera in the microbiome and specific HEI2015 components, such as vegetables and dairy for Hungatella, and whole fruits for Acidaminococus. Demographic characteristics were well-balanced between groups, with a significantly higher body mass index and lower physical activity observed in cases, underscoring the role of weight management in BCa risk. Associations between significant microbial genera identified from BCa cases and dietary intakes were identified, which highlights the potential of the gut microbiome as a source of biomarkers for BCa risk assessment. This study calls attention to the complex interplay between the gut microbiome, lifestyle factors including diet, and BCa risk.

Behavioral and Cognitive Performance Following Exposure to Second-Hand Smoke (SHS) from Tobacco Products Associated with Oxidative-Stress-Induced DNA Damage and Repair and Disruption of the Gut Microbiome.

Exposure to second-hand Smoke (SHS) remains prevalent. The underlying mechanisms of how SHS affects the brain require elucidation. We tested the hypothesis that SHS inhalation drives changes in the gut microbiome, impacting behavioral and cognitive performance as well as neuropathology in two-month-old wild-type (WT) mice and mice expressing wild-type human tau, a genetic model pertinent to Alzheimer's disease mice, following chronic SHS exposure (10 months to ~30 mg/m3). SHS exposure impacted the composition of the gut microbiome as well as the biodiversity and evenness of the gut microbiome in a sex-dependent fashion. This variation in the composition and biodiversity of the gut microbiome is also associated with several measures of cognitive performance. These results support the hypothesis that the gut microbiome contributes to the effect of SHS exposure on cognition. The percentage of 8-OHdG-labeled cells in the CA1 region of the hippocampus was also associated with performance in the novel object recognition test, consistent with urine and serum levels of 8-OHdG serving as a biomarker of cognitive performance in humans. We also assessed the effects of SHS on the percentage of p21-labeled cells, an early cellular marker of senescence that is upregulated in bronchial cells after exposure to cigarette smoke. Nuclear staining of p21-labeled cells was more prominent in larger cells of the prefrontal cortex and CA1 hippocampal neurons of SHS-exposed mice than in sham-exposed mice, and there was a significantly greater percentage of labelled cells in the prefrontal cortex and CA1 region of the hippocampus of SHS than air-exposed mice, suggesting that exposure to SHS may result in accelerated brain aging through oxidative-stress-induced injury.

Best practice for wildlife gut microbiome research: A comprehensive review of methodology for 16S rRNA gene investigations.

Extensive research in well-studied animal models underscores the importance of commensal gastrointestinal (gut) microbes to animal physiology. Gut microbes have been shown to impact dietary digestion, mediate infection, and even modify behavior and cognition. Given the large physiological and pathophysiological contribution microbes provide their host, it is reasonable to assume that the vertebrate gut microbiome may also impact the fitness, health and ecology of wildlife. In accordance with this expectation, an increasing number of investigations have considered the role of the gut microbiome in wildlife ecology, health, and conservation. To help promote the development of this nascent field, we need to dissolve the technical barriers prohibitive to performing wildlife microbiome research. The present review discusses the 16S rRNA gene microbiome research landscape, clarifying best practices in microbiome data generation and analysis, with particular emphasis on unique situations that arise during wildlife investigations. Special consideration is given to topics relevant for microbiome wildlife research from sample collection to molecular techniques for data generation, to data analysis strategies. Our hope is that this article not only calls for greater integration of microbiome analyses into wildlife ecology and health studies but provides researchers with the technical framework needed to successfully conduct such investigations.

Experimental methods modestly impact interpretation of the effect of environmental exposures on the larval zebrafish gut microbiome.

Rapidly growing fields, such as microbiome science, often lack standardization of procedures across research groups. This is especially the case for microbiome investigations in the zebrafish (Danio rerio) model system, which is quickly becoming a workhorse system for understanding the exposure-microbiome-physiology axis. To guide future investigations using this model system, we defined how various experimental decisions affect the outcomes of studies on the effects of exogenous exposure on the zebrafish gut microbiome. Using a model toxicant, benzo[a]pyrene (BaP), we assessed how each of two dissection methods (gut dissection vs. whole fish), three DNA extraction kits (Qiagen Blood & Tissue, Macherey-Nagel NucleoSpin, and Qiagen PowerSoil), and inclusion of PCR replicates (single vs. pooled triplicate reactions) affected our interpretation of how exposure influences the diversity and composition of the gut microbiome, as well as our ability to identify microbiome biomarkers of exposure. We found that inclusion of PCR replicates had the smallest effect on our final interpretations, and the effects of dissection method and DNA extraction kit had significant effects in specific contexts, primarily in the cases of identifying microbial biomarkers.

Fecal Implants From App NL-G-F and App NL-G-F/E4 Donor Mice Sufficient to Induce Behavioral Phenotypes in Germ-Free Mice.

The gut microbiome and the gut brain axis are potential determinants of Alzheimer's disease (AD) etiology or severity and gut microbiota might coordinate with the gut-brain axis to regulate behavioral phenotypes in AD mouse models. Using 6-month-old human amyloid precursor protein (hAPP) knock-in (KI) mice, which contain the Swedish and Iberian mutations [APP NL-F (App NL-F)] or the Arctic mutation as third mutation [APP NL-G-F (App NL-G-F)], behavioral and cognitive performance is associated with the gut microbiome and APP genotype modulates this association. In this study, we determined the feasibility of behavioral testing of mice in a biosafety cabinet and whether stool from 6-month-old App NL-G-F mice or App NL-G-F crossed with human apoE4 targeted replacement mice is sufficient to induce behavioral phenotypes in 4-5 month-old germ-free C57BL/6J mice 4 weeks following inoculation. We also compared the behavioral phenotypes of the recipient mice with that of the donor mice. Finally, we assessed cortical Aß levels and analyzed the gut microbiome in the recipient mice. These results show that it is feasible to behaviorally test germ-free mice inside a biosafety cabinet. However, the host genotype was critical in modulating the pattern of induced behavioral phenotypes as compared to those seen in the genotype- and sex-match donor mice. Male mice that received stool from App NL-G-F and App NL-G-F/E4 donor genotypes tended to have lower body weight as compared to wild type, an effect not observed among donor mice. Additionally, App NL-G-F/E4 recipient males, but not females, showed impaired object recognition. Insoluble Aß40 levels were detected in App NL-G-F and App NL-G-F/E4 recipient mice. Recipients of App NL-G-F, but not App NL-G-F/E4, donor mice carried cortical insoluble Aß40 levels that positively correlated with activity levels on the first and second day of open field testing. For recipient mice, the interaction between donor genotype and several behavioral scores predicted gut microbiome alpha-diversity. Similarly, two behavioral performance scores predicted microbiome composition in recipient mice, but this association was dependent on the donor genotype. These data suggest that genotypes of the donor and recipient might need to be considered for developing novel therapeutic strategies targeting the gut microbiome in AD and other neurodegenerative disorders.

Pseudocapillaria tomentosa, Mycoplasma spp., and Intestinal Lesions in Experimentally Infected Zebrafish Danio rerio.

Intestinal neoplasms and preneoplastic lesions are common in zebrafish research facilities. Previous studies have demonstrated that these neoplasms are caused by a transmissible agent, and two candidate agents have been implicated: a Mycoplasma sp. related to Mycoplasma penetrans and the intestinal parasitic nematode, Pseudocapillaria tomentosa, and both agents are common in zebrafish facilities. To elucidate the role of these two agents in the occurrence and severity of neoplasia and other intestinal lesions, we conducted two experimental inoculation studies. Exposed fish were examined at various time points over an 8-month period for intestinal histopathologic changes and the burden of Mycoplasma and nematodes. Fish exposed to Mycoplasma sp. isolated from zebrafish were associated with preneoplastic lesions. Fish exposed to the nematode alone or with the Mycoplasma isolate developed severe lesions and neoplasms. Both inflammation and neoplasm scores were associated with an increase in Mycoplasma burden. These results support the conclusions that P. tomentosa is a strong promoter of intestinal neoplasms in zebrafish and that Mycoplasma alone can also cause intestinal lesions and accelerate cancer development in the context of nematode infection.

Diet and gut microbiome enterotype are associated at the population level in African buffalo.

Studies in humans and laboratory animals link stable gut microbiome "enterotypes" with long-term diet and host health. Understanding how this paradigm manifests in wild herbivores could provide a mechanistic explanation of the relationships between microbiome dynamics, changes in dietary resources, and outcomes for host health. We identify two putative enterotypes in the African buffalo gut microbiome. The enterotype prevalent under resource-abundant dietary regimes, regardless of environmental conditions, has high richness, low between- and within-host beta diversity, and enrichment of genus Ruminococcaceae-UCG-005. The second enterotype, prevalent under restricted dietary conditions, has reduced richness, elevated beta diversity, and enrichment of genus Solibacillus. Population-level gamma diversity is maintained during resource restriction by increased beta diversity between individuals, suggesting a mechanism for population-level microbiome resilience. We identify three pathogens associated with microbiome variation depending on host diet, indicating that nutritional background may impact microbiome-pathogen dynamics. Overall, this study reveals diet-driven enterotype plasticity, illustrates ecological processes that maintain microbiome diversity, and identifies potential associations between diet, enterotype, and disease.

Integrated analysis of behavioral, epigenetic, and gut microbiome analyses in AppNL-G-F, AppNL-F, and wild type mice.

Epigenetic mechanisms occurring in the brain as well as alterations in the gut microbiome composition might contribute to Alzheimer's disease (AD). Human amyloid precursor protein knock-in (KI) mice contain the Swedish and Iberian mutations (AppNL-F) or those two and also the Arctic mutation (AppNL-G-F). In this study, we assessed whether behavioral and cognitive performance in 6-month-old AppNL-F, AppNL-G-F, and C57BL/6J wild-type (WT) mice was associated with the gut microbiome, and whether the genotype modulates this association. The genotype effects observed in behavioral tests were test-dependent. The biodiversity and composition of the gut microbiome linked to various aspects of mouse behavioral and cognitive performance but differences in genotype modulated these relationships. These genotype-dependent associations include members of the Lachnospiraceae and Ruminococcaceae families. In a subset of female mice, we assessed DNA methylation in the hippocampus and investigated whether alterations in hippocampal DNA methylation were associated with the gut microbiome. Among other differentially methylated regions, we identified a 1 Kb region that overlapped ing 3'UTR of the Tomm40 gene and the promoter region of the Apoe gene that and was significantly more methylated in the hippocampus of AppNL-G-F than WT mice. The integrated gut microbiome hippocampal DNA methylation analysis revealed a positive relationship between amplicon sequence variants (ASVs) within the Lachnospiraceae family and methylation at the Apoe gene. Hence, these microbes may elicit an impact on AD-relevant behavioral and cognitive performance via epigenetic changes in AD-susceptibility genes in neural tissue or that such changes in the epigenome can elicit alterations in intestinal physiology that affect the growth of these taxa in the gut microbiome.

Phylogenetic Integration Reveals the Zebrafish Core Microbiome and Its Sensitivity to Environmental Exposures.

Zebrafish are increasingly used to study how environmental exposures impact vertebrate gut microbes. However, we understand little about which microbial taxa are common to the zebrafish gut across studies and facilities. Here, we define the zebrafish core gut microbiome to resolve microbiota that are both relatively robust to study or facility effects and likely to drive proper microbiome assembly and functioning due to their conservation. To do so, we integrated publicly available gut microbiome 16S gene sequence data from eight studies into a phylogeny and identified monophyletic clades of gut bacteria that are unexpectedly prevalent across individuals. Doing so revealed 585 core clades of bacteria in the zebrafish gut, including clades within Aeromonas, Pseudomonas, Cetobacterium, Shewanella, Chitinibacter, Fluviicola, Flectobacillus, and Paucibacter. We then applied linear regression to discern which of these core clades are sensitive to an array of different environmental exposures. We found that 200 core clades were insensitive to any exposure we assessed, while 134 core clades were sensitive to more than two exposures. Overall, our analysis defines the zebrafish core gut microbiome and its sensitivity to exposure, which helps future studies to assess the robustness of their results and prioritize taxa for empirical assessments of how gut microbiota mediate the effects of exposure on the zebrafish host.

Zebrafish microbiome studies make waves.

Zebrafish have a 50-year history as a model organism for studying vertebrate developmental biology and more recently have emerged as a powerful model system for studying vertebrate microbiome assembly, dynamics and function. In this Review, we discuss the strengths of the zebrafish model for both observational and manipulative microbiome studies, and we highlight some of the important insights gleaned from zebrafish gut microbiome research.

Gut Feelings Begin in Childhood: the Gut Metagenome Correlates with Early Environment, Caregiving, and Behavior.

Psychosocial environments impact normative behavioral development in children, increasing the risk of problem behaviors and psychiatric disorders across the life span. Converging evidence demonstrates that early normative development is affected by the gut microbiome, which itself can be altered by early psychosocial environments. However, much of our understanding of the gut microbiome's role in early development stems from nonhuman animal models and predominately focuses on the first years of life, during peri- and postnatal microbial colonization. As a first step to identify if these findings translate to humans and the extent to which these relationships are maintained after initial microbial colonization, we conducted a metagenomic investigation among a cross-sectional sample of early school-aged children with a range of adverse experiences and caregiver stressors and relationships. Our results indicate that the taxonomic and functional composition of the gut microbiome correlates with behavior during a critical period of child development. Furthermore, our analysis reveals that both socioeconomic risk exposure and child behaviors associate with the relative abundances of specific taxa (e.g., Bacteroides and Bifidobacterium species) as well as functional modules encoded in their genomes (e.g., monoamine metabolism) that have been linked to cognition and health. While we cannot infer causality within this study, these findings suggest that caregivers may moderate the gut microbiome's link to environment and behaviors beyond the first few years of life.IMPORTANCE Childhood is a formative period of behavioral and biological development that can be modified, for better or worse, by the psychosocial environment that is in part determined by caregivers. Not only do our own genes and the external environment influence such developmental trajectories, but the community of microbes living in, on, and around our bodies-the microbiome-plays an important role as well. By surveying the gut microbiomes of a cross-sectional cohort of early school-aged children with a range of psychosocial environments and subclinical mental health symptoms, we demonstrated that caregiving behaviors modified the child gut microbiome's association to socioeconomic risk and behavioral dysregulation.

Combined Effects of Three High-Energy Charged Particle Beams Important for Space Flight on Brain, Behavioral and Cognitive Endpoints in B6D2F1 Female and Male Mice.

The radiation environment in deep space includes the galactic cosmic radiation with different proportions of all naturally occurring ions from protons to uranium. Most experimental animal studies for assessing the biological effects of charged particles have involved acute dose delivery for single ions and/or fractionated exposure protocols. Here, we assessed the behavioral and cognitive performance of female and male C57BL/6J × DBA2/J F1 (B6D2F1) mice 2 months following rapidly delivered, sequential irradiation with protons (1 GeV, 60%), 16O (250 MeV/n, 20%), and 28Si (263 MeV/n, 20%) at 0, 25, 50, or 200 cGy at 4-6 months of age. Cortical BDNF, CD68, and MAP-2 levels were analyzed 3 months after irradiation or sham irradiation. During the dark period, male mice irradiated with 50 cGy showed higher activity levels in the home cage than sham-irradiated mice. Mice irradiated with 50 cGy also showed increased depressive behavior in the forced swim test. When cognitive performance was assessed, sham-irradiated mice of both sexes and mice irradiated with 25 cGy showed normal responses to object recognition and novel object exploration. However, object recognition was impaired in female and male mice irradiated with 50 or 200 cGy. For cortical levels of the neurotrophic factor BDNF and the marker of microglial activation CD68, there were sex × radiation interactions. In females, but not males, there were increased CD68 levels following irradiation. In males, but not females, there were reduced BDNF levels following irradiation. A significant positive correlation between BDNF and CD68 levels was observed, suggesting a role for activated microglia in the alterations in BDNF levels. Finally, sequential beam irradiation impacted the diversity and composition of the gut microbiome. These included dose-dependent impacts and alterations to the relative abundance of several gut genera, such as Butyricicoccus and Lachnospiraceae. Thus, exposure to rapidly delivered sequential proton, 16O ion, and 28Si ion irradiation significantly affects behavioral and cognitive performance, cortical levels of CD68 and BDNF in a sex-dependent fashion, and the gut microbiome.

Effects of Sub-Chronic MPTP Exposure on Behavioral and Cognitive Performance and the Microbiome of Wild-Type and mGlu8 Knockout Female and Male Mice.

Motor dysfunction is a hallmark of Parkinson's disease (PD); however, non-motor symptoms such as gastrointestinal dysfunction often arise prior to motor symptoms. Alterations in the gut microbiome have been proposed as the earliest event in PD pathogenesis. PD symptoms often demonstrate sex differences. Glutamatergic neurotransmission has long been linked to PD pathology. Metabotropic glutamate receptors (mGlu), a family of G protein-coupled receptors, are divided into three groups, with group III mGlu receptors mainly localized presynaptically where they can inhibit glutamate release in the CNS as well as in the gut. Additionally, the gut microbiome can communicate with the CNS via the gut-brain axis. Here, we assessed whether deficiency of metabotropic glutamate receptor 8 (mGlu8), group III mGlu, modulates the effects of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), on behavioral and cognitive performance in female and male mice. We studied whether these effects are associated with changes in striatal tyrosine hydroxylase (TH) levels and the gut microbiome. Two-week sub-chronic MPTP increased activity of female and male wild-type (WT) and mGlu8 knockout (KO) mice in the open field. MPTP also showed genotype- and sex-dependent effects. MPTP increased the time WT, but not KO, females and males spent exploring objects. In WT mice, MPTP improved sensorimotor function in males but impaired it in females. Further, MPTP impaired cued fear memory in WT, but not KO, male mice. MPTP reduced striatal TH levels in WT and KO mice but these effects were only pronounced in males. MPTP treatment and genotype affected the diversity of the gut microbiome. In addition, there were significant associations between microbiome α-diversity and sensorimotor performance, as well as microbiome composition and fear learning. These results indicate that specific taxa may directly affect motor and fear learning or that the same physiological effects that enhance both forms of learning also alter diversity of the gut microbiome. MPTP's effect on motor and cognitive performance may then be, at least in part, be mediated by the gut microbiome. These data also support mGlu8 as a novel therapeutic target for PD and highlight the importance of including both sexes in preclinical studies.

Market Integration Predicts Human Gut Microbiome Attributes across a Gradient of Economic Development.

Economic development is marked by dramatic increases in the incidence of microbiome-associated diseases, such as autoimmune diseases and metabolic syndromes, but the lifestyle changes that drive alterations in the human microbiome are not known. We measured market integration as a proxy for economically related lifestyle attributes, such as ownership of specific market goods that index degree of market integration and components of traditional and nontraditional (more modern) house structure and infrastructure, and profiled the fecal microbiomes of 213 participants from a contiguous, indigenous Ecuadorian population. Despite relatively modest differences in lifestyle across the population, greater economic development correlated with significantly lower within-host diversity, higher between-host dissimilarity, and a decrease in the relative abundance of the bacterium Prevotella. These microbiome shifts were most strongly associated with more modern housing, followed by reduced ownership of traditional subsistence lifestyle-associated items. IMPORTANCE Previous research has reported differences in the gut microbiome between populations residing in wealthy versus poorer countries, leading to the assertion that lifestyle changes associated with economic development promote changes in the gut microbiome that promote the proliferation of microbiome-associated diseases. However, a direct relationship between economic development and the gut microbiome has not previously been shown. We surveyed the gut microbiomes of a single indigenous population undergoing economic development and found significant associations between features of the gut microbiome and lifestyle changes associated with economic development. These findings suggest that even the earliest stages of economic development can drive changes in the gut microbiome, which may provide a warning sign for the development of microbiome-associated diseases.

The role of adaptive immunity as an ecological filter on the gut microbiota in zebrafish.

All animals live in intimate association with communities of microbes, collectively referred to as their microbiota. Certain host traits can influence which microbial taxa comprise the microbiota. One potentially important trait in vertebrate animals is the adaptive immune system, which has been hypothesized to act as an ecological filter, promoting the presence of some microbial taxa over others. Here we surveyed the intestinal microbiota of 68 wild-type zebrafish, with functional adaptive immunity, and 61 rag1- zebrafish, lacking functional B- and T-cell receptors, to test the role of adaptive immunity as an ecological filter on the intestinal microbiota. In addition, we tested the robustness of adaptive immunity's filtering effects to host-host interaction by comparing the microbiota of fish populations segregated by genotype to those containing both genotypes. The presence of adaptive immunity individualized the gut microbiota and decreased the contributions of neutral processes to gut microbiota assembly. Although mixing genotypes led to increased phylogenetic diversity in each, there was no significant effect of adaptive immunity on gut microbiota composition in either housing condition. Interestingly, the most robust effect on microbiota composition was co-housing within a tank. In all, these results suggest that adaptive immunity has a role as an ecological filter of the zebrafish gut microbiota, but it can be overwhelmed by other factors, including transmission of microbes among hosts.

The composition of the zebrafish intestinal microbial community varies across development.

The assembly of resident microbial communities is an important event in animal development; however, the extent to which this process mirrors the developmental programs of host tissues is unknown. Here we surveyed the intestinal bacteria at key developmental time points in a sibling group of 135 individuals of a model vertebrate, the zebrafish (Danio rerio). Our survey revealed stage-specific signatures in the intestinal microbiota and extensive interindividual variation, even within the same developmental stage. Microbial community shifts were apparent during periods of constant diet and environmental conditions, as well as in concert with dietary and environmental change. Interindividual variation in the intestinal microbiota increased with age, as did the difference between the intestinal microbiota and microbes in the surrounding environment. Our results indicate that zebrafish intestinal microbiota assemble into distinct communities throughout development, and that these communities are increasingly different from the surrounding environment and from one another.

Contribution of neutral processes to the assembly of gut microbial communities in the zebrafish over host development.

Despite their importance to host health and development, the communities of microorganisms associated with humans and other animals are characterized by a large degree of unexplained variation across individual hosts. The processes that drive such inter-individual variation are not well understood. To address this, we surveyed the microbial communities associated with the intestine of the zebrafish, Danio rerio, over developmental time. We compared our observations of community composition and distribution across hosts with that predicted by a neutral assembly model, which assumes that community assembly is driven solely by chance and dispersal. We found that as hosts develop from larvae to adults, the fit of the model to observed microbial distributions decreases, suggesting that the relative importance of non-neutral processes, such as microbe-microbe interactions, active dispersal, or selection by the host, increases as hosts mature. We also observed that taxa which depart in their distributions from the neutral prediction form ecologically distinct sub-groups, which are phylogenetically clustered with respect to the full metacommunity. These results demonstrate that neutral processes are sufficient to generate substantial variation in microbiota composition across individual hosts, and suggest that potentially unique or important taxa may be identified by their divergence from neutral distributions.

Ontogenetic Differences in Dietary Fat Influence Microbiota Assembly in the Zebrafish Gut.

UNLABELLED: Gut microbiota influence the development and physiology of their animal hosts, and these effects are determined in part by the composition of these microbial communities. Gut microbiota composition can be affected by introduction of microbes from the environment, changes in the gut habitat during development, and acute dietary alterations. However, little is known about the relationship between gut and environmental microbiotas or about how host development and dietary differences during development impact the assembly of gut microbiota. We sought to explore these relationships using zebrafish, an ideal model because they are constantly immersed in a defined environment and can be fed the same diet for their entire lives. We conducted a cross-sectional study in zebrafish raised on a high-fat, control, or low-fat diet and used bacterial 16S rRNA gene sequencing to survey microbial communities in the gut and external environment at different developmental ages. Gut and environmental microbiota compositions rapidly diverged following the initiation of feeding and became increasingly different as zebrafish grew under conditions of a constant diet. Different dietary fat levels were associated with distinct gut microbiota compositions at different ages. In addition to alterations in individual bacterial taxa, we identified putative assemblages of bacterial lineages that covaried in abundance as a function of age, diet, and location. These results reveal dynamic relationships between dietary fat levels and the microbial communities residing in the intestine and the surrounding environment during ontogenesis. IMPORTANCE: The ability of gut microbiota to influence host health is determined in part by their composition. However, little is known about the relationship between gut and environmental microbiotas or about how ontogenetic differences in dietary fat impact gut microbiota composition. We addressed these gaps in knowledge using zebrafish, an ideal model organism because their environment can be thoroughly sampled and they can be fed the same diet for their entire lives. We found that microbial communities in the gut changed as zebrafish aged under conditions of a constant diet and became increasingly different from microbial communities in their surrounding environment. Further, we observed that the amount of fat in the diet had distinct age-specific effects on gut community assembly. These results reveal the complex relationships between microbial communities residing in the intestine and those in the surrounding environment and show that these relationships are shaped by dietary fat throughout the life of animal hosts.

Immigrants in immunology: the benefits of lax borders.

The field of immunology has a long history of illuminating fundamental biological processes of critical importance to human health. From an outsider's perspective, the questions are profoundly philosophical and the experimental approaches are elegantly precise. Yet immunology can also appear impenetrable. Here we recount the experience of two graduate students from the fields of ecology and computer science, who have immigrated into immunological terrain attracted by systems-level questions. We argue that such migrations enrich the field of immunology, and that cultural and institutional changes are needed to promote more interdisciplinary explorations.