Diversity, distribution and physiology of the aerobic phototrophic bacteria in the mixolimnion of a meromictic lake.

The population of anoxygenic phototrophic bacteria in the aerobic zone of the meromictic Mahoney Lake was investigated using classical microbiological methods. This bacterial community was found to be very rich and diverse. Thirty-one new strains of the obligately aerobic phototrophic bacteria, and two new purple nonsulfur strains, were isolated in pure cultures and preliminarily characterized. The isolates contain a variety of carotenoids, bacteriochlorophyll a incorporated into pigment protein complexes, and are morphologically and physiologically diverse. These properties indicate a diversity of adaptations to the stratified environments of this meromictic lake. Phylogenetically all isolated strains belong to the alpha subclass of Proteobacteria.