Regulation of intracellular H+ balance in Zymomonas mobilis 113 during the shift from anaerobic to aerobic conditions

Abstract

The energetics, enzyme activities and end-product synthesis of Zymomonas mobilis 113 in continuous culture were studied after the shift from an anaerobic to an aerobic environment. Aeration diminished ethanol yield and lactic acid concentration, but increased glucose consumption rate and production of acetic acid. After the shift to aerobic conditions reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H]-oxidase activity was stimulated. Washed cell suspensions consumed oxygen with glucose, lactate and ethanol as substrates. The aerobic Z. mobilis 113 regulated their intracellular redox balance by production and reoxidation of the end products, coupled with the formation of NAD(P)H. An increase in transmembrane pH gradient (ΔpH) and a decrease in intracellular ATP concentration were observed after the shift to aerobic conditions. At low medium redox potential (Eh) values the H+ balance was regulated in an energy-independent way via end-product excretion. Under aerobic conditions this was supplemented by ATP-dependent H+ excretion by the membrane H+-ATPase.