For investigation of the effects of aeration on nitrite- and nitrate-transforming activities of various heterotrophic bacteria, a series of coefficients of the oxygen absorption rate (Kd, 8-99 × 10-7 mol/ml·min·atm) in 500-ml shaking flasks were determined by varying plug types and culture volumes. Bacillus badius I-73, which neither shows denitrification activity nor utilize nitrate as a nitrogen source, consumed nitrite and accumulated nitrate at all Kd values at which experiments were conducted. In B. subtilis I-41, which does show denitrification activity, the manner of nitrite and nitrate conversion was influenced by the culture time and Kd, and the direction of conversion was changed from reduction to oxidation, as the Kd of the culture increased. Pseudomonas pavonaceae, another denitrification-positive strain, metabolized both nitrite and nitrate to more reduced compounds at low Kd, and the direction of conversion changed from reduction to oxidation at Kd = 20 × 1017 mol/ml·min·atm. Such switching behavior was also observed when P. pavonaceae was cultured continuously during variation of the aeration conditions with supply of pure oxygen. Many other denitrification-positive strains behaved similarly to P. pavonaceae, and showed their own critical Kd, the point at which the direction of nitrite metabolism changed. The results of intact-cell reaction experiments indicate that this switching might be caused by inhibition and repression of nitrite-reducing activity, and by stimulation of nitrite-oxidizing activity by oxygen.
All Science Journal Classification (ASJC) codes
- Applied Microbiology and Biotechnology