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Gut bacterial symbionts can support animal nutrition by facilitating digestion and providing valuable metabolites. While the composition of gut symbiont communities shifts with host development in holometabolous insects, changes in symbiotic roles between immature and adult stages are not well documented, especially in ants. Here, we explored the metabolic capabilities of microbiomes sampled from herbivorous turtle ant (Cephalotessp.) larvae and adult workers through genomic and metagenomic screenings and targetedin vitrometabolic assays. We reveal that larval guts harbor bacterial symbionts from the Enterobacteriales, Lactobacillales and Rhizobiales orders, with impressive metabolic capabilities, including catabolism of plant and fungal recalcitrant fibers common in turtle ant diets, and energy-generating fermentation. Additionally, several members of the specialized turtle ant adult gut microbiome, sampled downstream of an anatomical barrier that dams large food particles, show a conserved potential to depolymerize many dietary fibers and other carbohydrates. Symbionts from both life stages have the genomic capacity to recycle nitrogen, synthesize amino acids and B-vitamins, and perform several key aspects of sulfur metabolism. We also document, for the first time in ants, an adult-associated Campylobacterales symbiont with an apparent capacity to anaerobically oxidize sulfide, reduce nitrate, and fix carbon dioxide. With help of their gut symbionts, including several bacteria likely acquired from the environment, turtle ant larvae appear as an important component of turtle ant colony digestion and nutrition. In addition, the conserved nature of the digestive, energy-generating, and nutritive capacities among adult-enriched symbionts suggests that nutritional ecology of turtle ant colonies has long been shaped by specialized, behaviorally-transferred gut bacteria with over 46 million years of residency.

Gastric cancer is the third most common cancer in the world andHelicobacter spp. being one of the main factors responsible for development of cancer. AlongsideHelicobacterthe microbiota of the stomach mucosa may also play an important role in gastric cancer progression. Previously we had established that MyD88 deficient mice rapidly progressed to neoplasia when infected withH. felis. Thus, in order to assess the role of microbiota in gastric cancer progression we measured the changes in microbial diversity of the stomach in mice with different genotypic backgrounds (Wild type (WT), MyD88 deficient (MyD88−/−), mice deficient in the Toll/IL-1R (TIR) domain-containing adaptor-inducing interferon-β (TRIF,Triflps2), and MyD88 and Trif deficient (MyD88−/−and Trif−/−)double knockout (DKO) mice), both in uninfected andHelicobacterinfected mice and its correlation of these changes with gastric cancer progression. We observed that there was an overall reduction in microbial diversity post infection withH. felisacross all genotypes.Campylobacteraleswere observed in all infected mice, with marked reduction in abundance at 3 and 6 months in MyD88−/−mice. This low abundance ofH. pyloricould facilitate dominance of other organisms of microbiome likeLactobacilliales. A sharp increase inLactobacillialesin infected MyD88−/−and DKO mice at 3 and 6 months was observed as compared to Trif−/−and WT mice suggesting its possible role in gastric cancer progression. This was further reinforced upon comparison ofLactobacillusratio with histological data suggesting thatLactobacillalesis closely associated withHelicobacterinfection and gastric cancer progression. Thus, this study firstly suggests that difference in genotypes could define the stomach microbiome and make it more susceptible to development of gastric cancer uponHelicobacterinfections. Secondly the increase inLactobacillalescould contribute to faster development of gastric cancer and serve as a probable bio marker for fast progressing form of gastric cancer.

Geothermal springs are barely affected by environmental conditions aboveground as they are continuously supplied with subsurface water with little variability in chemistry. Therefore, changes in their microbial community composition and function, especially over a long period, are expected to be limited but this assumption has not yet been rigorously tested. Toward closing this knowledge gap, we applied whole metagenome sequencing to 17 water samples collected between 2010 and 2016 (two to four samples per year) from the Thermopyles sulfur geothermal springs in central Greece. As revealed by 16S rRNA gene fragments recovered in the metagenomes, Epsilonproteobacteria-related operational taxonomic units (OTUs) dominated most samples, while grouping of samples based on OTU abundances exhibited no apparent seasonal pattern. Similarities between samples regarding functional gene content were high, especially in comparison to other surface water systems in Greece, with all samples sharing >70% similarity in functional pathways. These community-wide patterns were further confirmed by analysis of metagenome-assembled genomes (MAGs), which showed - in addition- that novel species and genera of the chemoautotrophic Campylobacterales order dominated the springs. These MAGs carried different pathways for thiosulfate and/or sulfide oxidation coupled to carbon fixation pathways. Overall, our study showed that even in the long term, functions of microbial communities in a moderately hot terrestrial spring remain stable, driving presumably the corresponding stability in community structure.