Cyanide inhibits respiration yet stimulates aerobic growth of Zymomonas mobilis

Abstract

Potassium cyanide at submillimolar concentrations (20-500 µM) inhibited the high respiration rates of aerobic cultures of Zymomonas mobilis but, remarkably, stimulated culture growth. In batch culture, after an extended lag phase, exponential growth persisted longer, resulting in higher biomass densities. In aerobic chemostat cultures, elevated biomass concentration was observed in the presence of cyanide. This growth stimulation effect is attributed to decreased production of the inhibitory metabolite acetaldehyde at lowered respiration rates, when more reducing equivalents are channelled to alcohol dehydrogenase. Growth in the presence of cyanide did not alter the membrane cytochrome content. In non-growing cyanide-preincubated cells, with ethanol as the respiratory substrate, cyanide increased ATP levels ; in such cells, a large part of the cyanide-sensitive respiration was inhibited within a few seconds after ethanol addition, while inhibition of the rest of respiration took several minutes. The more cyanide-sensitive respiration was apparently energy-nongenerating, and was absent in membrane preparations. Pelleting of membranes from cell-free extracts produced ' soluble ' fractions in which a btype haem was detectable by reduced minus oxidized difference spectroscopy. The function of the Z. mobilis respiratory chain in cell growth and respiratory protection, and the possible physiological role of aerobic generation of inhibitory metabolites, are discussed.

Respiratory behaviour of a Zymomonas mobilis adhB::kanr mutant supports the hypothesis of two alcohol dehydrogenase isoenzymes catalysing opposite reactions

“…It is well established that the maximum value of Y ETOH in Z. mobilis catabolism under anaerobic conditions is close to 0.51 g of ethanol per gram of consumed glucose [18,21], and that under aerobic growth conditions Y ETOH is lower due to competition for NADH between the respiratory chain and ethanol synthesis [15]. In the aerobic chemostat culture of the mutant strain, we found Y ETOH to be 0.22 g g À1 , which constitutes 43% of the maximum value.…”

“…Ethanol concentration was determined by gas chromatography (Varian). Acetaldehyde was assayed using the alcohol dehydrogenase reaction, and glucose was assayed with the glucose oxidase method, as described previously [15]. Cell concentration was determined as optical density at 550 nm, and dry cell mass of the suspensions was calculated by reference to a calibration curve.…”

Cytochrome bd Oxidase, Oxidative Stress, and Dioxygen Tolerance of the Strictly Anaerobic Bacterium Moorella thermoacetica

“…Cyanide (1 mM) and azide (2 mM) inhibited both endogenous and substrate-dependent O 2 uptake up to 70% in whole-cell suspensions, indicating that most of the endogenous and exogenous substrate-dependent consumption of dioxygen follows an azide-and cyanide-sensitive pathway. Cyanide inhibition of O 2 consumption by whole cells has been reported in other bacteria, including acetogens (7,37,61).…”

Production of ethanol from mesquite (Prosopis juliflora (SW) D.C.) pods mash by Zymomonas mobilis and Saccharomyces cerevisiae

“…Tano and Buzzato (2003) noted a low ethanol production (29 gL -1 ) by Z. mobilis in sugar cane juice during 24 hrs of fermentation in stirring condition. Anaerobic cultures of Z. mobilis have showed the highest ethanol yields (0.51 g glucose -1 ) in different substrates, while small yields (0.13 g glucose -1 ) have been noted in aerobic cultures (Kalnenieks et al 2000;Prasad et al 2007). Previous studies suggested a possible average yield of ethanol from mesquite pods of up to 260 L per ton, while for sugar cane it is purposed an average yield of up to 80 L per ton (Silva et al 2003, Silva et al 2007).…”