Insects are the most abundant animals on Earth, and the microbiota within their guts play important roles by engaging in beneficial and pathological interactions with these hosts. In this study, we comprehensively characterized insect-associated gut bacteria of 305 individuals belonging to 218 species in 21 taxonomic orders, using 454 pyrosequencing of 16S rRNA genes. In total, 174,374 sequence reads were obtained, identifying 9,301 bacterial operational taxonomic units (OTUs) at the 3% distance level from all samples, with an average of 84.3 (±97.7) OTUs per sample. The insect gut microbiota were dominated by Proteobacteria (62.1% of the total reads, including 14.1% Wolbachia sequences) and Firmicutes (20.7%). Significant differences were found in the relative abundances of anaerobes in insects and were classified according to the criteria of host environmental habitat, diet, developmental stage, and phylogeny. Gut bacterial diversity was significantly higher in omnivorous insects than in stenophagous (carnivorous and herbivorous) insects. This insect-order-spanning investigation of the gut microbiota provides insights into the relationships between insects and their gut bacterial communities.

Objective: Cerebral amyloidosis and severe tauopathy in the brain are key pathological features of Alzheimer’s disease (AD). Despite a strong influence of the intestinal microbiota on AD, the causal relationship between the gut microbiota and AD pathophysiology is still elusive.Design: Using a recently developed AD-like pathology with amyloid and neurofibrillary tangles (ADLP^APT) transgenic mouse model of AD, which shows amyloid plaques, neurofibrillary tangles and reactive gliosis in their brains along with memory deficits, we examined the impact of the gut microbiota on AD pathogenesis.Results: Composition of the gut microbiota in ADLP^APTmice differed from that of healthy wild-type (WT) mice. Besides, ADLP^APTmice showed a loss of epithelial barrier integrity and chronic intestinal and systemic inflammation. Both frequent transfer and transplantation of the faecal microbiota from WT mice into ADLP^APTmice ameliorated the formation of amyloid β plaques and neurofibrillary tangles, glial reactivity and cognitive impairment. Additionally, the faecal microbiota transfer reversed abnormalities in the colonic expression of genes related to intestinal macrophage activity and the circulating blood inflammatory monocytes in the ADLP^APTrecipient mice.Conclusion: These results indicate that microbiota-mediated intestinal and systemic immune aberrations contribute to the pathogenesis of AD in ADLP^APTmice, providing new insights into the relationship between the gut (colonic gene expression, gut permeability), blood (blood immune cell population) and brain (pathology) axis and AD (memory deficits). Thus, restoring gut microbial homeostasis may have beneficial effects on AD treatment.

Background: Our understanding of the gut microbiota of animals is largely based on studies of mammals. To better understand the evolutionary basis of symbiotic relationships between animal hosts and indigenous microbes, it is necessary to investigate the gut microbiota of non-mammalian vertebrate species. In particular, fish have the highest species diversity among groups of vertebrates, with approximately 33,000 species. In this study, we comprehensively characterized gut bacterial communities in fish. Results: We analyzed 227 individual fish representing 14 orders, 42 families, 79 genera, and 85 species. The fish gut microbiota was dominated by Proteobacteria (51.7%) and Firmicutes (13.5%), different from the dominant taxa reported in terrestrial vertebrates (Firmicutes and Bacteroidetes). The gut microbial community in fish was more strongly shaped by host habitat than by host taxonomy or trophic level. Using a machine learning approach trained on the microbial community composition or predicted functional profiles, we found that the host habitat exhibited the highest classification accuracy. Principal coordinate analysis revealed that the gut bacterial community of fish differs significantly from those of other vertebrate classes (reptiles, birds, and mammals). Conclusions: Collectively, these data provide a reference for future studies of the gut microbiome of aquatic animals as well as insights into the relationship between fish and their gut bacteria, including the key role of host habitat and the distinct compositions in comparison with those of mammals, reptiles, and birds.

In this study, we investigated the abundance and diversity of single-stranded DNA (ssDNA) viruses in fecal samples from five healthy individuals through a combination of serial filtration and CsCl gradient ultracentrifugation. Virus abundance ranged from 10 ⁸ to 10 ⁹ per gram of feces, and virus-to-bacterium ratios were much lower (less than 0.1) than those observed in aquatic environments (5 to 10). Viral DNA was extracted and randomly amplified using phi29 polymerase and analyzed through high-throughput 454 pyrosequencing. Among 400,133 sequences, an average of 86.2% viromes were previously uncharacterized in public databases. Among previously known viruses, double-stranded DNA podophages (52 to 74%), siphophages (11 to 30%), myophages (1 to 4%), and ssDNA microphages (3 to 9%) were major constituents of human fecal viromes. A phylogenetic analysis of 24 large contigs of microphages based on conserved capsid protein sequences revealed five distinct newly discovered evolutionary microphage groups that were distantly related to previously known microphages. Moreover, putative capsid protein sequences of five contigs were closely related to prophage-like sequences in the genomes of three Bacteroides and three Prevotella strains, suggesting that Bacteroides and Prevotella are the sources of infecting microphages in their hosts.

Bacteriophages are central members and potential modulators of the gut microbiome; however, the ecological and evolutionary relationships of gut bacteria and phages are poorly understood. Here we investigated the abundance and diversity of lysogenic bacteria (lysogens) in the bacterial community of C57BL/6J mice by detecting integrated prophages in genomes reconstructed from the metagenome of commensal bacteria. For the activities of lysogens and prophages, we compared the prophage genomes with the metagenome of free phages. The majority of commensal bacteria in different taxa were identified as lysogens. More lysogens were found among Firmicutes and Proteobacteria, than among Bacteroidetes and Actinobacteria. The prophage genomes shared high sequence similarity with the metagenome of free phages, indicating that most lysogens appeared to be active, and that prophages are spontaneously induced as active phages; dietary interventions changed the composition of the induced prophages. By contrast, CRISPR-Cas systems were present in few commensal bacteria, and were rarely active against gut phages. The structure of the bacteria-phage infection networks was “nested-modular”, with modularity emerging across taxonomic scales, indicating that temperate phage features have developed over a long phylogenetic timescale. We concluded that phage generalists contribute to the prevalence of lysogeny in the gut ecosystem.

Human gut microbiota plays important roles in harvesting energy from the diet, stimulating the proliferation of the intestinal epithelium, developing the immune system, and regulating fat storage in the host. Characterization of gut microbiota, however, has been limited to western people and is not sufficiently extensive to fully describe microbial communities. In this study, we investigated the overall composition of the gut microbiota and its host specificity and temporal stability in 20 Koreans using 454-pyrosequencing with barcoded primers targeting the V1 to V3 region of the bacterial 16S rRNA gene. A total of 303,402 high quality reads covered each sample and 8,427 reads were analyzed on average. The results were compared with those of individuals from the USA, China and Japan. In general, microbial communities were dominated by five previously identified phyla: Actinobacteria, Firmicutes, Bacteroidetes, Fusobacteria, and Proteobacteria. UPGMA cluster analysis showed that the species composition of gut microbiota was host-specific and stable over the duration of the test period, but the relative abundance of each member fluctuated. 43 core Korean gut microbiota were identified by comparison of sequences from each individual, of which 15 species level phylotypes were related to previously-reported butyrate-producing bacteria. UniFrac analysis revealed that human gut microbiota differed between countries: Korea, USA, Japan and China, but tended to vary less between individual Koreans, suggesting that gut microbial composition is related to internal and external characteristics of each country member such as host genetics and diet styles.