The regulation of hydrogenase formation as a differentiating character of strains of Paracoccus denitrificans.

Paracoccus denitrificans strains Stanier 381 (DSM 65), Morris (DSM 413), and Vogt 11 (DSM 415) and eleven newly isolated strains were compared with respect to the localization of hydrogenase and its regulation. In all strains hydrogenase was found to be membrane-bound and not able to reduce pyridine nucleotides. The enzyme was inducible in strain 381 and was found only in cells grown with hydrogen as the sole hydrogen donor; in cells grown under mixotrophic or heterotrophic conditions the hydrogenase activity was zero. In all other strains hydrogenase was constitutive and was present in cells grown under autotrophic, mixotrophic and heterotrophic conditions. Under the latter conditions the specific hydrogenase activity was even higher than under mixotrophic conditions.