SUMMARY: strain 473 can grow aerobically with various -alkanes as the sole source of carbon and energy. Anaerobic growth, with nitrate as the terminal electron acceptor, occurs with a variety of carbon substrates but not with -alkanes. This bacterium has now been grown in continuous culture with malate, malate and octane, or octane as the carbon source. The effects of varying the dissolved oxygen tension on the cell yield, key enzyme activities, the cytochrome content and the ability to metabolize components of the medium were determined in order to assess whether alkane oxidation and nitrate dissimilation could occur concomitantly in poorly aerated cultures.

The activities of dissimilatory nitrate and nitrite reductases were maximal in bacteria which were grown anaerobically. However, during growth with malate at oxygen tensions between 2 and 3 mmHg, nitrate reductase activity was readily detected, but nitrite reductase activity and cytochrome were absent. It is therefore concluded that the synthesis and activity of nitrate and nitrite reductases are not coordinately regulated. In contrast, the activities of enzymes for octane oxidation were greatest in cultures grown aerobically. When octane was the sole carbon source, growth continued when the dissolved oxygen tension decreased to below 2 mmHg, but no growth occurred in the absence of oxygen. Although alkane oxidation occurred during growth in poorly aerated cultures, the cell yield on octane was higher in the absence of nitrate than in its presence.


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