Abstract
This chapter reviews achievements in mercury microbiology research during the past 35 years and identifies areas in which more information is needed to complete our understanding of how microbes in the diverse ecological niches that exist on earth interact with mercury. Mercury is a potent toxic substance, the toxicity of which is elicited at very low concentrations. Although all chemical forms of mercury are toxic, public health concerns are focused on methylmercury (MeHg). The major routes of human exposure to this toxic element are through the consumption of contaminated fish, where mercury is mostly present in its methylated form. This is the result of the bioaccumulation and biomagnification of MeHg in the aquatic food chain. MeHg is a neurotoxin that causes pathologies ranging from mild numbness of the extremities to blindness, loss of balance, and death. Because MeHg is more toxic than other forms of mercury, and mercury is mostly deposited in the environment in its ionic form, the biogeochemical cycling of mercury in the environment plays a key role in modulating mercury toxicity. Furthermore, microbial transformations play critical roles in the mercury geochemical cycle, and understanding the mechanisms of these transformations is essential for controlling mercury transport and accumulation in the biosphere.