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Beneckea natriegens provides an interesting system for the study of respiratory control in bacteria as it apparently has four different recognisable cytochrome oxidases. From inhibitor studies on cell free extracts a branched electron transport chain has been proposed for this organism. The individual branches of the electron transport chain are distinguished by their differing affinity for oxygen and sensitivity to inhibition by cyanide. It has been suggested that the multiple oxidases present in this organism function at different medium dissolved oxygen tensions and may be associated with differing efficiencies of phosphorylation. The respiratory control and growth physiology of Beneckea natriegens was studied using continuous culture techniques. As a preliminary to this investigation the inorganic ion requirement of this organism was examined in batch culture and a basal salts medium formulated to facilitate the operation of a carbon limited chemostat culture at a medium glucose feed concentration of 4.0 gl-1. The results obtained in batch culture were confirmed in continuous culture (D = 0.34 h-1) where a linear relationship between bacterial biomass and substrate concentration (0.5 to 4,0 gl-1 glucose) was observed, indicative of carbon limitation. The effect of growth rate on growth physiology was investigated and the molar growth yields from glucose and oxygen were found to be dependent on, and to increase with, increasing growth rate. The in situ respiration rate of B. natriegens was directly proportional to the dilution rate. The 'potential' respiration rate, however, was independent of the growth rate and remained at a value higher than the in situ respiration rate, the latter increased with increase in the dilution rate. The cytochrome content of bacteria decreased with increasing growth rate, and no positive correlation between bacterial cytochrome content and respiration rate was observed. To assess whether branching of the electron transport system occurred under physiological conditions, B. natriegens was grown at various medium dissolved oxygen tensions in glucose limited chemostat culture and the effect of medium dissolved oxygen tension on growth yield, respiration and cytochrome composition examined. The results indicated that the metabolic rate and growth efficiency of this organism, as indicated by the q02' qC02 and Yglc' was little affected by changes in the dissolved oxygen tension over the range |
