OXYGEN, HYDROGEN AND NITROGEN-FIXATION IN AZOTOBACTER

This paper discusses four aspects of the H-2-uptake hydrogenase (Hup)- dependent respiration in Azotobacter. (1): Competition between isogen ic Hup(+) and Hup(-) strains of Azotobacter chroococcum containing the vanadium nitrogenase showed that the Hup(+) strain dominated under ca rbon-, phosphate- or intrinsic N-2-limited conditions but not under O- 2-, sulphate- or Fe-limitation. (2): A Cyd(-) mutant of Azotobacter vi nelandii was capable of catalysing O-2-dependent (HH)-H-3 uptake, indi cating that H-2-dependent respiration linked to a high affinity (O-2) oxidase system. (3): High-O-2-adapted A, chroococcum showed lower spec ific nitrogenase activity at low ambient O-2 and 16 degrees C than did low-O-2-adapted A. chroococcum, suggesting that the high-affinity oxi dases were inactivated at high ambient O-2. (4): A second region of DN A, distinct from the main hup gene region, involved in H-2-dependent r espiration is described. (C) 1997 Elsevier Science Ltd.