Assessment of the Physiological Groups of Bacteria from Salt Lakes and Euxinic Sediments Involved in Sulfur Cycle, Therapeutical Mud Formation, and Regeneration

The biogeochemical cycle of sulfur is important in the diagenesis of organic matter sedimented in saline and euxinic lakes leading to sapropel formation. The study aimed to determine the numerical densities of physiological groups of sulfur bacteria in water and sediment samples from five Romanian saline and euxinic lakes with therapeutical properties in order to assess their peloidogen regeneration potential. Bacterial communities that metabolize sulfur compounds were monitored in lakes with different salinity values: Techirghiol, Amara, Sovata-Black Lake, Ursu Lake, and Braila Salt Lake by multiple tube method. Statistical results revealed the interdependence between sulfoxidizing bacteria/SO42- in sediments, while the reductive microorganisms fraction/metabolic products (H2S/Corg./Norg) separately evolved in the economy of peloidogenic ecosystems. In the lakes, Techirghiol, Amara, and Braila Salt Lake, the dominant role in the specific microbiota belonged to sulfate/sulfur-reducing bacteria, and the formed peloid was sulfurous-sapropelic in Techirghiol Lake or sulfurous-mineral in Amara Lake and Braila Salt Lake. In the hypersaline, meromictic, and heliothermal lakes of Sovata, the sulfur metabolism was predominantly oxidative, made by sulfoxidizing bacteria in higher numerical densities, with the accumulation of SO42- ions in the strongly hydrated aqueous phase of mineral sediments.