THE EFFECT OF WASTEWATER EFFLUENT ON THE GUT CONTENT MICROBIOME OF RAINBOW DARTER (ETHEOSTOMA CAERULEUM)

Abstract

The microbiome plays an important role in host physiology and can be influenced by species, diet, and environment. Municipal wastewater effluent contains a mixture of chemicals including antibiotics and antimicrobials that may affect the gut microbiome of fish living downstream of these discharges. Thus, this study examines the effect of wastewater treatment plant (WWTP) effluent on the gut microbiome of wild rainbow darter (Etheostoma cearuleum), and examines how the gut microbiome of wild fish changes in the lab. Fish were collected from sites upstream and downstream of 2 major WWTPs along the central Grand River and gut contents were aseptically sampled. After extracting gDNA, nested PCR of the V3-V4 region of the 16S rRNA gene, and Illumina sequencing were performed. The gut microbiome of exposed fish had increased bacterial diversity and was dominated by Proteobacteria, which has been linked to altered health outcomes in mammals. Next, rainbow darters were collected from a reference site on the Grand River. Fish were sampled in the field, after a 14 day lab acclimation, and after a 28 day exposure to environmental stressors (WWTP effluent or triclosan, an antimicrobial found in WWTP effluent). Surprisingly, there were no changes in the microbiome after exposure to environmental stressors. Major changes were observed between the field and laboratory fish suggesting that environment and diet are important factors influencing the gut microbiome. Changes in the gut microbiome continued up to 42 days in the lab, indicating longer acclimation periods may be needed. This study showed that effluents altered the gut microbiome of fish in the field, but not in the laboratory for unknown reasons. Laboratory studies indicated that transitioning to a new environment may require greater than 14 days before achieving a stable microbiome.