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Cyanide inhibits respiration yet stimulates aerobic growth of Zymomonas mobilis

Institute of Microbiology and Biotechnology, University of Latvia, Kronvalda boulv. 4,Riga LV-1586, Latvia¹
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, S10 2TN Sheffield, UK²

Author for correspondence: Robert K. Poole. Tel: +44 114 222 4447. Fax: +44 114 272 8697. e-mail: r.poole{at}sheffield.ac.uk

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 b-type 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.

Keywords: Zymomonas mobilis, cyanide sensitivity, respiratory protection, cytochromes, acetaldehyde

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