研究期間：10108~10207;Due to its unique physicochemical property, mercury (Hg) has been considered as a global pollutant of concern. It has been widely recognized that microorganisms play a key role in governing biogeochemical cycles of Hg in the environment. To date while microbial Hg reduction has been well documented in aerobic resistant prokaryotes carrying mer operons that are capable of reducing Hg(II) to Hg(0), little work has been undertaken to elucidate mer activities among anaerobes and other possible microbially mediated reactions associated with Hg redox chemistry in anaerobic environments. Recent observations, however, suggest that Hg sensitive iron-reducing bacteria (FeRB) reduce Hg(II) constitutively. In anoxic zones with low levels of Hg, this newly discovered process might more critically affect Hg speciation then the inducible mer-meidated reduction. Relevantly, it has been suggested that Hg-contaminated groundwater, which may be super-saturated with Hg(0), can result from stimulation of microbial activities in subsurface environments. This strongly imply that conventional in situ bio-remedial actions relying on stimulation of indigenous microbial activities to enhance microbial degradation and reductive transformation of pollutants in contaminated subsurface sediments should be cautioned, as they might inadvertently mobilize Hg into groundwater. Consequently, a better understanding of the processes mediated by anaerobic microbial consortia that control the mobility of Hg in aquifers is crucial for future environmental management and remediation efforts. Because iron has been considered as one of the most abundant elements for microbes to respire in groundwater environments, we propose to conduct laboratory microcosm experiments to explore the interactions between Hg and dissimilatory iron-reducers. We hypothesize that under environmentally relevant iron-reducing conditions, subsurface microorganisms may reduce Hg(II) by redox-active macromolecules and/or by a coupled biotic/abiotic pathway controlled by the formation of reactive secondary Fe(II)/Fe(III) minerals. To test these hypotheses, by conducting microcosm experiments coupled with molecular biology we will (i) distinguish the roles of electron transport chains from that of biogenic Fe(II) in the reduction of Hg(II) and directly test the role of known components of the electron transport chain of model FeRB in this activity; (ii) investigate the role of biogenic Fe(II)/Fe(III) minerals in Hg(II) reduction by examining production of these minerals during growth of FeRB on ferrihydrite and by exogenously supplied and well characterized Fe(II)/Fe(III) mineral phases; as well as (iii) examine biotic/abiotic pathways for Hg(II) reduction in enrichment cultures derived from subsurface sediments. The proposed research has the potential to greatly reduce the uncertainty associated with predicting the movement of Hg in the subsurface. Also, information gained from this study will be applicable to the study of other contaminants in natural and engineered systems.
