HYDROXYLAMINE METABOLISM IN PSEUDOMONAS PB16 - INVOLVEMENT OF A NOVELHYDROXYLAMINE OXIDOREDUCTASE

Pseudomonas strain PB16, a Gram-negative heterotrophic nitrifying bact erium closely related to Pseudomonas azalaica on the basis of 16 S rDN A analysis, was able to use hydroxylamine as an additional energy sour ce during growth in acetate limited chemostat cultures giving an incre ased biomass yield. In aerobically growing cells of Pseudomonas PB16 o nly 50% of supplemented hydroxylamine could be recovered as nitrite. I n addition to nitrite, N2O could be detected in the chemostat off-gas, indicating combined heterotrophic nitrification and aerobic denitrifi cation. The maximum specific hydroxylamine oxidizing activity observed was 450 nmol per min per mg dry weight, with a K-s of approximately 4 0 mu M. Upon addition of hydroxylamine to the medium, Pseudomonas PB16 induced a soluble 132 KDa dimeric hydroxylamine oxidoreductase. The e nzyme had a pH optimum of 9, and did not contain spectroscopic feature s typical for cytochromes, which is in contrast to hydroxylamine oxido reductases found in autotrophic bacteria.