Despite efforts to decrease mercury emissions, chronic exposure to the neurotoxicant methylmercury (MeHg) continues to be a global problem that contributes to disparities in risk for neurological and metabolic diseases. Herein we engineer a human commensal gut bacterium, Bacteroides thetaiotaomicron (Bt), to detoxify MeHg by heterologous expression of organomercury lyase (MerB) and mercuric reductase (MerA) genes derived from a resistant bacterium isolated from Hg-polluted mines. We demonstrate that Bt