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Community Dynamics of Pelagic Bacteria in The High Mountain Lake Sulzata—Rila Mountain, Bulgaria

ABSTRACT This study analyzed the temporal dynamics in the abundance and composition of pelagic bacterial communities inhabiting Sulzata Lake (2 500 m a.s.l.), a lake of glacial origin situated in Rila National Park (Rila Mountain, Bulgaria). Epifluorescence microscopic counting and amplified rDNA restriction analysis (ARDRA) were used to monitor the succession of planktonic bacterial communities. Sulzata Lake was well abundant in bacteria (on average (69.13±81.1) X 105 cells ml−1), as their number fluctuated drastically depending on the values of environmental determinants. ARDRA analysis yielded high bacterial diversity resulting in different band patterns. The observed changes in ARDRA profiles were a consequence of strongly fluctuating population sizes under the fluctuation of environmental determinants causing changes in the rate of dominance, hence in the bacterial diversity (H': 0.69–2.07) and low levels of genetic similarity (0-65%) between the pelagic bacterial communities. The diversity of different ecotypes increases adaptation fitness which guarantees stability and drives the evolution of an ecosystem under extreme and extremely variable conditions.