Carbon source utilization and accumulation of respiration-related substances by freshwater Thioploca species.

Carbon source utilization of Thioploca species from freshwater and brackish lakes in Japan was investigated. Microautoradiography demonstrated that freshwater and brackish Thioploca samples assimilate acetate. In addition, vertical nitrate transportation by freshwater Thioploca was examined by measuring substances accumulated in Thioploca filaments. The filaments of Thioploca sp. from Lake Biwa, a Japanese mesotrophic lake, contained nitrate at concentrations higher than ambient by two to three orders of magnitude. They also accumulated high concentrations of sulfate and abundant elemental sulfur. The results suggest that the Thioploca-specific strategy for sulfur oxidation, migration with accumulated nitrate, is effective even in freshwater habitats of lower sulfide supply.