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.

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Résumé La diminution de l'O₂ dissous de 90 à 50% de la saturation dans un fermenteur, a affecté de manière négative tant la production de biomasse deRhizobium meliloti ATCC 9930 que le nombre de cellules revivifiables, bien que l'oxygène ne fut jamais limitant. Des quantités diminuées d'oxygène dissous ou une diminution accidentelle de la concentration en oxygène dissous, ont également causé une acidification appréciable du milieu de culture résultant de l'accumulation de CO₂ dans le milieu. L'ajout de CO₂ au gaz d'aération a affecté tant la production de biomasse que le temps moyen de génération, proportionnellement à la concentration de CO₂; l'effet sur le nombre de cellules revivifiables était moins prononcé.R. meliloti peut être considéré comme un microorganisme modérément sensible au CO₂. Une bonne croissance deR. meliloti requiert, entre autres, non seulement une aération (oxygénation) suffisante, mais aussi une bonne ventilation du CO₂ engendré pendant la fermentation.

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Publication Number NRCC No. 32389     

Conditions leading to precipitation of ribulose bisphosphate carboxylase-oxygenase differ from those leading to enzyme activation

The relation between conditions leading to precipitation and/or activation of Ru-P₂ carboxylase have been explored in order to test the hypothesis that conformational changes leading to precipitation might be identical to those which are presumed to lead to enzyme activation. From the results of kinetic and solubility studies, we conclude that this hypothesis is not valid, since changes in solubility of Ru-P₂ carboxylase occur ten times as fast as changes in enzyme kinetics.