| 英文摘要: | Methylmercury is a very potent neurotoxin produced by some microbes. Once formed, methylmercury can easily bio-magnify, that is, the concentrations of methylmercury in organisms increase as one goes up the food chain. Other microbes have the ability to degrade methylmercury, thus limiting this process of bio-magnification. These known systems of methylmercury degradation, however, do not appear to be significant in most environments. Recent work, however, has found that different microbes, through a process yet to be full elucidated, degrade methylmercury under more environmentally relevant conditions. This process may thus be very important in controlling methylmercury bioaccumulation, and its toxicity. In this project we will delineate this process and determine how wide-spread it may be in the environment.
Methane-oxidizing bacteria, i.e., methanotrophs, are widespread in the environment, but their impact on biogeochemical cycling of mercury, has only just been investigated. The investigators have recently found that methanotrophs bind and demethylate substantial amounts of methylmercury (MeHg), a neurotoxic form of mercury that is generated via anaerobic microbial activity. What is remarkable is that methanotrophs do not have merB, encoding for the well-characterized organomercurial lyase, indicating that methanotrophs use an as yet unknown mechanism to demethylate MeHg. Further, methanotrophic-mediated MeHg degradation was observed under environmentally relevant conditions (i.e., nanomolar concentrations of mercury and circumneutral pH), unlike the organomercurial lyase, which is operative only under conditions rarely seen in the environment. As such, it appears that the methanotrophic-mediated MeHg degradation is much more environmentally significant than the canonical merB-mediated pathway. The objectives of this proposal are thus to determine how methanotrophs take up and degrade MeHg. Investigators will examine a suite of methanotrophs that span the phylogenetic and physiological diversity of these microbes as well as several mutants of one of these species to determine how these microorganisms take up and demethylate MeHg, and the impact of MeHg uptake and degradation on growth, activity and transcriptome. |