Capacity for Nitrate Respiration as a New Aspect of Metabolism of the Filamentous Sulfur Bacteria of the Genus Thiothrix

Capacity of Thiothrix species (T. lacustris strains AS and BLT, T. caldifontis G1(T), T. unzii A1(T), and T. eikelboomii AR3(T)) for anaerobic respiration in the presence of nitrate was discovered. The dynamics of nitrate reduction to nitrite was studied and the coupling of this process to thiosulfate oxidation was shown. The investigated Thiothrix representatives performed anaerobic thiosulfate-dependent reduction of nitrate only to nitrite. The presence of the narG gene, encoding the alpha-subunit of respiratory nitrate reductase NarGHI, was revealed in the cells. The induction of this gene expression was shown for the T. lacustris strain AS under anaerobic conditions of growth. The activity of several enzymes involved in the conversion of reduced sulfur compounds was determined.