Chronic embryo-larval exposure of fathead minnows to the pharmaceutical drug metformin: survival, growth, and microbiome responses

Metformin is a glucose-lowering drug taken by a large number of people and is released into waterways through municipal wastewater effluents. The current study investigated the effects of metformin on the microbiome of early-life stage fathead minnow (Pimephales promelas) using 16S rRNA gene amplicon sequencing to determine microbial community composition, and alpha and beta diversity. Larvae were exposed to measured concentrations of 0.02(for controls), and 3.44, 33.6 and 269 micrograms/L of metformin for 21-days (5 d in the embryo, and 16 days post-hatch). The larvae microbiome was dominant in Proteobacteria and Firmicutes, with small increases in Proteobacteria and decreases in Firmicutes with increasing exposure to metformin. No treatment effects were found for microbiome diversity measures.