Sulfite-Reducing Clostridia and their Participation in Methane and Hydrogen Sulfide Formation in the Bottom Sediments of Water Objects and Streams of the ETR South

The article discusses the role of sulfite-reducing clostridia in methane and hydrogen oxide formation in bottom sediments. The examined materials have been accumulated in the course of expeditions carried out at 25 water objects and streams of the subarid zone of the Southern ETR with different mineralization and the degree of anthropogenic stress, as well as via an experiment aimed at detection of the ability of sulfite-reducing clostridia to produce reduced gases. In the majority of samples of bottom sediments in water objects of the Southern ETR, including mud sediments of lakes that are used for therapeutic purposes, the amount of sulfite-reducing clostridia exceeds the normative levels by an order of magnitude. The maximum abundance (10(6)-10(7) CFU/g) was recorded in the nearshore zone of the southeastern part of the Taganrog Bay, thus implying fecal pollution. As a rule, the highest abundance is restricted to the higher (0-2 and/or 2-5 cm) layers. A close relationship was found to exist between the concentrations of methane and hydrogen sulfide, as well as the abundance of sulfite-reducing clostridia in the bottom sediments. The results of the laboratory experiment imply the ability of sulfite-reducing clostridia to produce methane and hydrogen sulfide. It is supposed that sulfite-reducing clostridia, as well as methanogens and sulfate-reducing microorganisms, participate in the generation of methane and hydrogen sulfide in situ in bottom sediments and therapeutic muds.