Characterization of Metal-Reducing Microorganisms in Walker Lake: A Terminal Saline Desert Lake

Metal-reducing microorganisms are increasingly being recognized as an essential component of aquatic microbial ecosystems involved in decomposition of organic matter. Alkaliphilic microbial reduction from alkaline lakes is a little studied field and one particular ecosystem, Walker Lake, presents the opportunity to investigate alkaliphilic metal reducers in their native ecological setting. Walker lake is a terminal, saline, desert lake with pH 9.4, Walker Lake samples of surface and deep sediments and water column samples from 0, 10, 5, 15, 17.5, 19 m depths were cultured by serial dilution in synthetic Walker Lake medium and supplemented separately with Hydrous Ferric Oxide (HFO), Fe Citrate (Fe CR), Fe nitrilotriacetic acid or Fe NTA a chelating agent), and manganese oxide (MnO2) as terminal electron acceptors. Dilutions were duplicated and the highest cell activity was produced in sediment samples, ranging from 105-107 cells/ml, when inoculated with HFO, Fe Citrate, and Fe NTA and 103-104 cells/ml were observed in the sediment samples with Mn(IV) as the terminal electron acceptor. Microbial isolation, using overlay technique and serial dilution, was attempted with moderate success. Comparative data analysis of Walker Lake physical parameters collected in 2013-2014 and data collected in previous Walker Lake studies in 2008 indicated a lake with decreasing water depth, increasing salinity (2.5 mg/l to 18 mg/l) and a subsequent loss of stratification. Alkaliphilic metal-reduction in Walker Lake is still a developing story with upwards of 105-107 cells/ml of Fe-reducing microbes in the sediment