EFFECTS OF ILLUMINATION AND PH ON THE GROWTH-RATE AND NITROGENASE ACTIVITY OF RHODOBACTER-CAPSULATUS GROWN WITH OR WITHOUT MOLYBDENUM

Growth and nitrogenase activity were studied in turbidostat cultures o f Rhodobacter capsulatus grown with or without molybdenum under differ ent illumination regimes and pH. The saturating light intensity was th e same (20-22 W/m(2)) for cultures grown with or without Mo, but the g rowth rate was higher in the presence of Mo. In either culture, nitrog enase activity, determined from the rates of acetylene reduction or hy drogen evolution, was not affected by light in the range of growth-sat urating intensities. In the range of growth-limiting intensities, nitr ogenase activity, measured by both methods, and the rate of nitrogenas e synthesis decreased. Cultures grown without Mo less efficiently util ized light energy for growth; unlike Mo-supplemented cultures, they re tained nitrogenase activity and the ability to grow at pH 9, and the o ptimum pH for measuring their nitrogenase activity was dependent on th e pH maintained during cultivation.