Authors

Abstract

Host-associated microbial dynamics are influenced by dietary and im- mune factors, but how exogenous microbial exposure shapes host-microbe dynam- ics remains poorly characterized. To investigate this phenomenon, we characterized the skin, rectum, and respiratory tract-associated microbiota in four aquarium- housed dolphins daily over a period of 6 weeks, including administration of a probi- otic during weeks 4 to 6. The environmental bacterial sources were also character- ized, including the animals’ human handlers, the aquarium air and water, and the dolphins’ food supply. Continuous microbial exposure occurred between all sites, yet each environment maintained a characteristic microbiota, suggesting that the major- ity of exposure events do not result in colonization. Small changes in water physico- chemistry had a significant but weak correlation with change in dolphin-associated bacterial richness but had no influence on phylogenetic diversity. Food and air mi- crobiota were the richest and had the largest conditional influence on other micro- biota in the absence of probiotics, but during probiotic administration, food alone had the largest influence on the stability of the dolphin microbiota. Our results sug- gest that respiratory tract and gastrointestinal epithelium interactions with air- and food-associated microbes had the biggest influence on host-microbiota dynamics, while other interactions, such as skin transmission, played only a minor role. Finally, direct oral stimulation with a foreign exogenous microbial source can have a pro- found effect on microbial stability.