| Summary: | The object of this work was to study some of the biochemical effects of various oxygen-transfer conditions in submerged cultures of a facultative anaerobe, \(Klebsiella\) \(aerogenes\) N.C.I.B. 418. A well-mixed laboratory fermenter with extensive instrumentation was used to reproduce and monitor some possible effects of 'cyclic aeration', a phenomenon experienced by microorganisms in most industrial fermentations. Batch and continuous cultures were carried out both aerobically and anaerobically, using a synthetic glycerol-salts medium. 'Cyclic aeration' was simulated by 'intermittent aeration', air and nitrogen being supplied alternately to the fermenter over a five-minute cycle. The aerobic enzymes (glycerol kinase and glycerol-3-phosphate dehydrogenase) and anaerobic enzymes (glycerol dehydrogenase and dihydroxyacetone kinase) involved in the conversion of glycerol to dihydroxyacetone phosphate were assayed in each culture sample. An aerobic→anaerobic transition, indicated most noticeably by a marked reduction of cell density, was found to take place rather sharply as the aeration time per cycle was progressively reduced. The transition point and the sharpness of the transition were dependent on oxygen-transfer efficiency during the aeration period, as well as on the aeration time per cycle, and resulted in reductions in the levels of the aerobic enzymes and increases in the levels of the anaerobic enzymes. Specific carbon dioxide production increased as 'aeration condition' was reduced to the point of fully anaerobic growth; its measurement was used, together with that of culture dissolved oxygen tension, to follow the progress of the transition. It is suggested that the determination of the complement of these enzymes could be used to assess the effectiveness of oxygen distribution in industrial fermenters.
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