Bacterial oxidation of arsenite at Hot Creek: Characterization of biofilm communities and isolation of novel bacteria associated with aquatic macrophytes (California)

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 α-proteobacterium that was isolated using an enrichment-based isolation technique with arsenite concentrations much higher than ambient levels. Values of the kinetic parameters K_s(3.4 ± 2.2 μM) and V _max (1.81 ± 0.58 × 10−12 μmole·cell −1·min−1) were determined for AOL15. The K_s 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 β-proteobacteria of the genus Hydrogenophaga, were isolated from solid media. Molecular techniques suggested that β-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 (MIPN) analysis. The normalized MEPN values were 1.4 × 109 total cells/g dry wt. plant and 3.3 × 108 oxidizer cells/g dry wt. plant. These estimates suggest that the oxidizers constitute a significant fraction (on average 24%) of the overall biofilm community.