MICROBIAL DIVERSITY IN SEDIMENTS OF LAKE CHAKA: AN INLAND ALKALINE LAKE IN NORTHEASTERN CHINA

Lake Chaka is an inland hypersaline lake in Northwestern China. To study microbial communities in relation to the ecological and tectonic evolution of this area, we collected water samples and sediment cores. A strong evaporation (2464 mm evaporation/224 mm rainfall/year) in this area has made Lake Chaka near-dry and high salinity (21%, six times seawater). Its pH equals 7.4. A core of 42 x 5 cm (length x diameter) was collected and dissected into 2-cm subsumples. Phospholipid fatty acid analysis (PLFA) and DNA extraction were performed on selected subsamples. Viable biomass ranged from 2.05 x 108 at the water-sediment interface to 1.65 x 107 cells/g at 42cm depth. Biomass was inversely correlated with microbial physiological status. PLFA profiles indicated the presence of Proteobacteria, Firmicutes, and metal and sulfate reducers. The bacterial and archaeal 16S ribosomal rDNA was amplified followed by phylogenetic analyses. The bacterial community in the interface sample was diverse and contained aerobes. Clone sequences were related to Gram positive, Bacteriodetes, sulfur-oxidizing gamma proteobacteria and other bacteria from diverse environments. Some sequences were related to low G + C Gram positive bacteria or clones from an alkaline lake (Mono Lake, CA) and the anoxic sediments underlying cyanobacterial mats of two hypersaline ponds in Mediterranean salterns. With increasing depth, sequences related to low G + C Gram positives became predominant. Other sequences in the deeper samples were related to bacteria or clones from deep-sea sediment, hydrothermal vents and saline lakes. Among archaeal sequences, two were related to ancient salt deposits, and another two were related to extreme halophiles, however, others were not related to any cultured archaea. Crenarchaeota and Euryarchaeota sequences were present in the interface sample, with dominance of Euryarchaeota. Archaeal sequences in the interface sample were similar to those found in soils. With increasing depth, sequences related to those from saline-lake and deep-sea sediments and methanogenic halophilic archaea became increasingly important. In conclusion, microbial communities in Lake Chaka shifted in response to environmental gradients.