Abstract
By using membrane-bound dehydrogenases, Gluconobacter oxydans characteristically accomplishes single-step oxidation of many polyols and quantitative release of the oxidation product into the medium. These cells typically differentiate by forming intracytoplasmic membranes (ICM) after exponential growth on glycerol. Earlier experiments demonstrated that glycerol-grown cells containing ICM oxidized glycerol more rapidly than cells which were harvested during exponential growth and lacked ICM (Claus et al., J. Bacteriol. 123:1169-1183). This report demonstrates that ICM are also formed after growth on sorbitol. Sorbitol-grown, ICM-containing maximum stationary-phase (MSP) cells showed from 50 to 300% greater oxidation (respiration) rates on mannitol, glycerol, glucose, meso-erythritol, and meso-inositol than did exponential-phase (EXP) cells which lacked ICM. Both EXP and MSP cells exhibited maximum sorbitol oxidation at pH 5.0, 38 degrees C, and 5% (wt/vol) sorbitol. When assayed under these optimum conditions, ICM-containing MSP cells demonstrated a 72% increase in respiration on sorbitol compared with that of EXP cells lacking ICM (oxygen quotients of 3,100 and 1,800, respectively). Gas chromatographic studies showed that sorbose was the only detectable product released from cells during oxygen quotient analysis. The specific activity of particulate-bound sorbitol dehydrogenase from ICM-containing MSP cells was twice that obtained from particulate fractions prepared from EXP cells lacking ICM. These results show that neither ICM formation after exponential growth nor increased respiration of other polyols is dependent upon the polyol used to grow cells. Our results suggest that increased respiratory activity of MSP cells is caused both by ICM formation and by increased synthesis (or activity) of the polyol dehydrogenases found in these membranes.