the microbial populations of saline environments are physiologically adapted to extreme conditions of salinity and oxygen shortage, and are major responsibles of chemical element returns to the atmosphere in salt water ecosystems. the mar chiquita lake, an extensive saline lake of the province of córdoba, argentina (provincial reserve and ramsar site), has been scarcely explored, particularly in its microbiological aspects. here we present a first approach to the knowledge of its microbial communities and other environmental parameters. we collected water and sediment samples from the coast and open waters of different depth, and evaluated chemical and physical parameters and abundance of microbial metabolic groups involved in the degradation of organic compounds and nutrient release. the results showed an abundant bacterial community constituted by heterotrophic microorganisms with aerobic respiration and fermentation, and by amonifiers, nitrate-reducers, nitrogen fixers, hydrogen sulphide-oxidisers, sulfate-reducers, and iron-oxidisers. the ammonium-oxidisers were less abundant. the abundance of different metabolic groups responded to factors associated with oxygen availability and both allochthonous and autochthonous organic carbon availability. similarly to other saline lakes of the world, our results suggest that in this lake: (1) sulfate reduction would be the most important metabolism, (2) the presence of aerobic organisms in high salinity environments would respond to the interaction with oxygenic phototrophic organisms (cianobacteria); and (3) nitrogen metabolism is very conservative due to the high abundance of fixers and the scarcity of nitrate-reducer microorganisms.