Effects of Cultural Conditions on Nitrate Reductase in Photobacterium sepia

Abstract

SUMMARYThe effect of cultural conditions on the growth and nitrate reductase activity of a bacterium, now identified as Photobacterium sepia, were examined. The bacterium grew well with ammonium chloride, ammonium nitrate or potassium nitrate as sole nitrogen source. Nitrate reductase activity was markedly decreased in organisms deficient in molybdenum or iron and in organisms grown a t high oxygen pressures. The P. sepia enzyme is thus similar to nitrate reductases from other bacteria. The P. sepia enzyme is constitutive; it is present in organisms grown with ammonium chloride in the absence of nitrate; the ammonium radical did not depress enzyme activity. Under certain conditions (NH,NO, medium, 10 yo, v/v, 0, in N,) molybdenum (10 pg./l.) depressed the nitrate reductase activity, but this effect was annulled by repeated subcultivation in molybdenumdeficient medium. Vanadium and especially tungsten, also inhibited the enzyme. The uptake of nitric oxide was decreased in organisms depleted of iron but was increased in organisms deficient in molybdenum. The behaviour of nitrate reductase preparations during fractionation whether from P. sepia grown with KNO, or with NH&1 suggests that the enzyme is the same from both sources.

Regulation of Nitrate Assimilation and Nitrate Respiration in Aerobacter aerogenes

“…One might expect that oxygen should not completely abolish nitrate reductase activity, because this would deprive the organism of the assimilatory function of the enzyme under aerobic conditions. Furthermore, it was reported that NH4+ repressess the formation of the assimilatory nitrate reductase in some organisms, e.g., fungi (1, 8) and yeast (17), whereas in bacteria, nitrate respiration apparently still occurs in the presence of NH4+ (6,7,13,20). We show that respiratory nitrate reductase is inactivated and that its synthesis is blocked by oxygen.…”

Nitrate Reduction and the Growth of Veillonella alcalescens

“…This latter generalization must be considered with reservation, however, for a soluble respiratory nitrate reductase has been reported in Spirillum itersonii (2). It appears, however, that all assimilatory nitrate reductases are inhibited or repressed by ammonium salts, whereas respiratory reductases are not inhibited (4,5,11,16).…”