Summary: has been studied during batch cultivation at pH 7 and 35° in a glucose + casein hydrolysate + vitamins and salts medium kept (i) anaerobic ( , – 400 to – 370 mV), (ii) aerated ( , – 50 to 0 mV; dissolved O, < 1 μM), and (iii) aerobic ( , + 100 mV; dissolved O, 40 to 50 μM). Short-term (4 to 6 h.) exposure to oxygen was not lethal, though at sufficiently high concentrations oxygen decreased the rate of glucose consumption, halted growth and prevented net synthesis of DNA, RNA and protein. Under these aerobic conditions the organism was drained of ‘reducing power’ and starved of energy – as evidenced by cessation of butyrate formation (but not of acetate production), and by a marked fall in intracellular ATP. These consequences of oxygenation were swiftly reversed when anaerobic conditions were re-established; ‘normal’ growth and glucose metabolism then resumed. There was no evidence of HO production, nor could the effects of oxygenation be attributed merely to its elevation of the culture . Thus oxygen (40 μM) inhibited growth even in a medium poised with dithiothreitol at – 50 mV, while growth and glucose metabolism continued unchecked when the of an anaerobic culture was maintained at +370 mV by addition of potassium ferricyanide.


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