Bacterial oxidation of arsenite at Hot Creek: characterization of biofilm communities and isolation of novel bacteria associated with aquatic macrophytes

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Hot Creek, a tributary of the Owens River in the Long Valley Caldera in California, contains naturally elevated concentrations of arsenic as a result of geothermal activity. This site is of particular interest because of its substantial impact on the quality of the drinking water supply for the City of Los Angeles. Previous studies revealed a rapid in situ oxidation of arsenite in Hot Creek. In this work, bacterial oxidation of arsenite is viewed from the perspective of cultivation-based studies (focusing on pure cultures of arsenite oxidizers) and molecular technique-based studies (surveying the community under ambient conditions). The cultivation-based techniques yielded four new arsenite oxidizers. One isolate, Agrobacterium albertimagni strain AOL15, is an [alpha]-proteobacterium that was isolated using an enrichment-based isolation technique with arsenite concentrations much higher than ambient levels. Values of the kinetic parameters [...] and [...] were determined for AOL15. The [...] is near the ambient concentration of arsenite in Hot Creek. However, molecular-based techniques suggested that AOL15 is not a significant member of the biofilm associated with submerged macrophytes. The other three oxidizers, YED1-18, YED6-4, and YED6-21, all [beta]-proteobacteria of the genus Hydrogenophaga, were isolated from solid media. Molecular techniques suggested that [beta]-proteobacteria are important members of the macrophyte surface community. In the molecular survey, one sequence from Clone #44 (partial) was found to be 99.6% identical to YED6-21. This result, coupled with the isolation of the Hydrogenophaga oxidizers from a million-fold dilution of a suspension of cells from the macrophyte surface, suggests that the Hydrogenophaga are significant members of this community and may be the dominant arsenite oxidizers. The densities of total and oxidizer cells associated with the submerged macrophytes in Hot Creek were estimated using most probable number (MPN) analysis. The normalized MPN values were [...] total cells/g dry wt. plant and [...] oxidizer cells/g dry wt. plant. These estimates suggest that the oxidizers constitute a significant fraction (on average 24%) of the overall biofilm community