The Digestive Microbiome Diversity of the Least Killifish, <scp> <i>Heterandria formosa</i> </scp> , and Its Implications for Host Adaptability to Varying Trophic Levels

Symbiotic microbes, in associations with aquatic hosts, aid in the acquisition of nutrients, breakdown xenobiotics, and contribute to immune system function. If associations with microbial communities facilitate host adaptation to different ecosystems, understanding the important ecological factors that act as drivers of differences among conspecific populations' microbiomes can help conservation efforts to promote beneficial interactions between fish and their microbiome for freshwater fish species facing rapid environmental changes. Here we describe the microbial communities in the gut of a freshwater fish, Heterandria formosa, in spring habitats using 16S rRNA sequencing. We quantified microbiota composition and diversity among springs ranging from oligotrophic to near eutrophic to determine the extent to which the microbiota are associated with different environmental conditions. We found higher microbial richness at sites with lower nutrient load stress. At more eutrophic sites, we detected the potential for increased metabolic capacity for pollutant degradation in the associated microbiota. We noted greater phylogenetic similarity between more environmentally similar sites, supporting previous evidence that the microbiota of freshwater fish is influenced by site water chemistry. Our findings bring to light microbial taxa and pathways that might play critical roles in the bioremediation of stressful environmental conditions.