Formation of the Dehydrogenases for Lactate, Ethanol and Butanediol in the Strictly Aerobic Bacterium Alcaligenes eutrophus

Abstract

475 ~ ~~ ~~Lactate, ethanol and butanediol were excreted when Alcaligenes eutrophus was exposed to severely restricted aeration. This indicated the presence of dehydrogenases which are not normally present in aerobically grown cultures of this strictly aerobic bacterium. When grown in the presence of measurable dissolved oxygen concentrations. A. eutrophus strain N9A and a double mutant defective in the formation of poly-3-hydroxybutanoic acid and in the utilization of 3-hydroxybutanoate did not synthesize alcohol, lactate or butanediol dehydrogenases. However, when bacteria were subsequently incubated for 10 to 25 h under restricted aeration conditions that permitted respiration rates of only about 3 to 15 o//o of the maximum value, the above enzymes were formed with specific activities up to 0-75 pmol min-1 (mg protein)-l. The identity of metabolites excreted as well as the nature of the enzymes formed could be correlated with the distinctive relative respiration rates enforced on the bacteria during incubation.The results indicate that A. eutrophus contains genetic information which is not expressed under ordinary cultural conditions. The significance for retention of the dormant genetic material in strictly aerobic bacteria is discussed.

Physiology and molecular genetics of poly(β‐hydroxyalkanoic acid) synthesis in Alcaligenes eutrophus

“…The formation of pyridine nucleotide-dependent alcohol and iactate dehydrogenase is concomitantly induced (Schlegel and Vollbrecht, 1980). If PHB-negative mutants are cultivated under these conditions, the cells excrete organic acids such as p-hydroxybutyrate and pyruvate, into the medium (Vollbrecht etai, 1979;Steinbuchel and Schlegel, 1989).…”

Alcohol dehydrogenase gene from Alcaligenes eutrophus: subcloning, heterologous expression in Escherichia coli, sequencing, and location of Tn5 insertions

“…The ADH catalyzes the NAD(P)-dependent oxidation of ethanol, 2,3-butanediol, and acetaldehyde and the reduction of acetaldehyde, acetoin, and diacetyl (66). The wild type synthesizes this multifunctional ADH, together with an NAD-linked lactate dehydrogenase, only when the cells are cultivated under conditions of restricted oxygen supply (58). In addition to the ability to evolve molecular hydrogen (45,71) and to synthesize poly-,-hydroxybutyric acid (71), both enzymes appear to provide a safety valve for the release of excess reducing power in the absence of exogenous hydrogen acceptors such as oxygen or nitrate.…”

Expression of the Escherichia coli pfkA gene in Alcaligenes eutrophus and in other gram-negative bacteria

“…This bacterium is therefore unable to grow on fructose or gluconate in the absence of terminal electron acceptors like oxygen or nitrate. Despite its respiratory energy metabolism, typical fermentation enzymes (30) like an NAD-dependent lactate dehydrogenase (35)(36)(37) and an unspecific NAD(P)-dependent alcohol dehydrogenase (38) are derepressed if the cells are incubated under conditions of restricted oxygen supply (29), and the respective fermentation products are excreted into the medium (41). In addition, reduced pyridine nucleotides are reoxidized during the formation of poly-p-hydroxybutyrate (31) and to some extent during the evolution of molecular hydrogen, which is catalyzed by NAD-dependent hydrogenase (20).…”