Influence of oxygenation and carbon dioxide on the growth ofRhizobium meliloti in a fermenter.

A decrease in dissolved O2 from 90% to 50% saturation in a fermenter adversely affected both blomass production ofRhizobium meliloti ATCC 9930 and viable cell number, although oxygen was never limiting. Lower amounts of dissolved oxygen, or accidental decreases in dissolved oxygen concentration, also caused appreciable acidification of the culture broth, which was the result of CO2 accumulation in the medium. Adding CO2 to the aeration gas mixture affected both biomass production and mean generation time in proportion to the CO2 concentration; the effect on viable cell number was less pronounced.R. meliloti may be considered as a microorganism moderately sensitive to CO2. GoodR. meliloti growth requires, among other things, not only sufficient aeration (oxygenation) but also good ventilation of the CO2 evolved during the fermentation.