GLUCOSE-METABOLISM AND GLUCONIC ACID PRODUCTION BY ACETOBACTER-DIAZOTROPHICUS

Acetobacter diazotrophicus, a recently isolated nitrogen-fixing acidotolerant acetic acid bacterium, grew well in simple mineral media and exhibited high rates of gluconic acid formation. Glucose oxidation by the organism was less sensitive to low pH values than glucose oxidation by Gluconobacter oxydans. Growth and glucose oxidation were not affected by high gluconic acid concentrations. These observations indicate that A. diazotrophicus is an interesting organism for the industrial production of gluconic acid. The organism exhibited a high maintenance requirement (m(s) = 1.0 mmol glucose h-1 (g dry weight)-1) during glucose-limited growth in chemostat cultures at pH 3.5. Enzyme activities in cell-free extracts suggested that glucose metabolism in A. diazotrophicus proceeds exclusively via the hexose monophosphate pathway: the enzymes of the Embden-Meyerhof and Entner-Doudoroff pathways could not be detected. Roth the phosphorylative and direct oxidative pathways of glucose metabolism appeared to be operative. In addition to a pyridine nucleotide (strictly NAD)-dependent glucose dehydrogenase, A. diazotrophicus contained a dye-linked, probably pyrrolo-quinoline quinone (PQQ)-dependent, glucose dehydrogenase. The latter activity seemed to be primarily responsible for gluconic acid formation.