Seasonal Dynamics of the Bacterial Community in Lake Namco, the Largest Tibetan Lake

Seasonal variations of bacterial abundance and diversity in Lake Namco, the large and deep high altitude lake, were first investigated using flow cytometry enumeration and 16S rRNA gene clone library analysis. Bacterial abundance varied from 1.5 x 10(5) to 12.3 x 10(5) cells mL(-1) and exhibited a seasonal pattern that correlated with water temperature and phytoplankton abundance rather than nutrient. This indicated that temperature had a strong effect on bacterial abundance in cold and oligotrophic Lake Namco. Bacterial diversity and community compositions varied in different months. Bacterial community structure changes coincide with the variations of dissolved organic carbon and total nitrogen contents. The three best-represented bacterial groups in libraries, the Actinobacteria, Cyanobacteria, and Beta-proteobacteria, had distinct temporal niches and dominated the bacterial communities in January, May, and June, respectively. Ice cover and nutrient appeared to be of important factors in structuring the seasonal variation of bacterial community composition in Lake Namco.