ABSTRACT
Although the biogeochemical conditions that promote microbial arsenic mobilization are becoming clearer, it remains a major challenge to identify the organisms that have the potential to cause the reduction and mobilization of the metalloid among the complex microbial communities that exist in the subsurface. One approach that has proved useful is the application of Stable Isotope Probing (SIP), which can link the active fraction of a microbial community to a particular biogeochemical process. Here, sediments are supplemented with a 13Clabeled substrate, and the components of the microbial community that assimilate the substrate are identified by PCR-based analysis of the “heavy” labeled DNA or RNA separated from unlabeled “light” nucleic acids by ultracentrifugation. This technique has been used to identify active As(V)-respiring bacteria in Cambodian aquifer sediments (Lear et al., 2007) implicated in the reductive mobilization of arsenic (Rowland et al., 2007). With the addition of 13C-labeled acetate and As(V), most of which was associated with the mineral phases in the microcosms, an organism closely related to the arsenate-reducing organism Sulfurospirillum strain NP4 was identified. Functional gene analysis targeted the As(V) respiratory reductase gene (arrA) using highly specific primers, and identified gene sequences most closely related to those found in S. barnesii and G. uraniireducens.
