Abstract
The expression and in situ activity of the membrane-bound and periplasmic nitrate reductases have been assayed in Paracoccus denitrificans Pd1222 grown under a range of aeration regimes in malate-limited or butyrate-limited chemostat cultures. In butyrate-limited cultures the expression of periplasmic nitrate reductase and the rate of in situ nitrate reduction were high at all oxygen concentrations measured between 0% and 100% air saturation. By contrast, in malate-limited cultures expression of the periplasmic nitrate reductase was low at 80-100% air saturation but increased to a maximum between 20% and 50% air saturation. Aerobic nitrate reduction was much higher in butyrate-limited than in malate-limited cultures, demonstrating a significant role for this process during butyrate metabolism. The rate of nitrate respiration increased in both the malate- and butyrate-limited cultures as aerobic metabolism switched completely to anaerobic metabolism. Expression of the membrane-bound nitrate reductase could be detected in butyrate-limited chemostat cultures maintained at an oxygen level of 100% air saturation. No membrane-bound nitrate reductase was detectable under similar conditions in malate-limited cultures but expression was detected at oxygen concentrations of 50% air saturation and below. Taken together, the results show that the nature of the carbon substrate and oxygen concentration can both influence expression of the periplasmic and membrane-bound nitrate reductases. The conditions under which expression of the periplasmic nitrate reductase and aerobic nitrate respiration are maximal can be rationalized in terms of a role for the periplasmic nitrate reductase in dissipating excess reductant generated during oxidative metabolism of reduced carbon substrates.
Original language | English |
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Pages (from-to) | 3767-3774 |
Number of pages | 8 |
Journal | Microbiology |
Volume | 143 |
Issue number | 12 |
DOIs | |
Publication status | Published - Dec 1997 |
Keywords
- Aerobic nitrate respiration
- Denitrification
- Nitrate reductase
- Paracoccus denitrificans
- Redox balancing