N-198. Microbial Communities of a Saline, Alkaline Terminal Lake (Walker Lake, NV)

J. C. Bruckner1, C. H. Fritsen2, J. C. Memmot2, R. L. Hersey2, A. Heyvaert2, D. P. Moser1;
1Desert Research Inst., Las Vegas, NV, 2Desert Research Inst., Reno, NV.

Walker Lake is nitrogen-limited moderately saline (~1%), alkaline (pH 9.3) monomictic terminal lake in western NV. The lake’s volume has decreased ~75% over the past 100 years resulting in a 5-fold increase in total dissolved solids and in recent decades, summertime anoxia in the hypolimnion. Hypolimnetic accumulation of sulfide and ammonia and subsequent fluxes into the metalimnion are considered a danger to the lake’s threatened Lahontan cutthroat trout. To gain insights into the microbial communities present in this system, water column samples were collected before stratification (May 2007) and during the (anomalously early) autumnal turnover of October 2007. At the time of the autumn sampling, the bottom several meters were chemically and physically distinct from bulk lake water, suggesting it was a hypolimnetic remnant. Samples were analyzed using both molecular and culture-based methods. Direct counts (DAPI) indicated that despite the relatively high pH, Walker Lake contained cell numbers typical of a freshwater lake (~106 cells/ml). To evaluate community structure, 16S rRNA genes were PCR amplified from extracted nucleic acids and subjected to terminal restriction fragment length polymorphism (T-RFLP) analysis and molecular cloning. The results indicated changes in microbial community structure with depth, particularly with respect to the hypolimnetic bottom water sample. Preliminary cultivation efforts (May 2007) revealed an almost exclusively alkaliphilic microbial community (e.g. aerobic plate counts on R2A medium at pH 7.5 yielded no culturable organisms). Thus, for the autumn sampling, Walker-specific (pH 9.3-9.5) media formulations were developed based on the lake’s unique chemistry to target a range of expected microbial physiotypes. MPN analysis revealed (cells/ml) 104-106 aerobic heterotrophs, 102-105 nitrate reducers, 104 fermenters, 103-104 iron reducers, 103-105 So and 0-101 sulfate reducers. The high numbers of iron reducers vs. relatively low numbers of sulfate reducers suggested that metal-driven redox cycling may occur during summer stratification; a more comprehensive evaluation of microbial community structure is planned for the summer of 2008.

175/N. Molecular Microbial Ecology - Communities - III

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