This action funds an NSF Postdoctoral Research Fellowship in Biology for FY 2025. The fellowship supports research and training of the fellow that will contribute to biology in innovative ways. Many animals rely on gut microbes to break down toxins in their plant-based diet. In some insects and mammals, this “microbial facilitation” also helps detoxify ingested pesticides and pollutants. Release of human pharmaceuticals into the oceans has raised concerns about toxic effects on filter-feeding organisms like mussels, which cannot escape toxic stress. This research will investigate how the blue mussel Mytilus edulis and its gut microbiome interact to break down a toxic pharmaceutical pollutant. Understanding how microbial breakdown of pollutants affects mussel health will improve predictions of how bivalves will adapt to more foreign substances in their environment. Detoxifying microbes in the gut could help mussel populations tolerate toxic threats and position microbiome health as a key concern in their conservation and aquaculture. Undergraduate research mentorship and career pathway development constitute key broader impact activities. The research will involve three major approaches using the pharmaceutical contaminant carbamazepine (CBZ), which accumulates in and is toxic to marine bivalves. Mussels from a CBZ-free habitat will be exposed to a range of CBZ concentrations in microcosms, and the tolerance of the mussel and its gut microbiome (combined “holobiont”) assess