Respective effects of sodium and chloride ions on filament formation and growth and ethanol production in Zymomonas mobilis fermentations

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Aims:To elucidate the separate effects of the cation and anion in Zymomonas mobilis cultures inhibited by NaCl.Methods and Results:In batch cultures containing 0·175 mol l−1 NaCl, Z. mobilis developed filaments and growth and ethanol production were inhibited. Chloride ions (added as 0·175 mol l−1 NH4Cl) produced similar filamentous growth, while sodium ions at the same concentration (as Na2SO4) did not. Growth and ethanol production were more strongly inhibited by Na2SO4 than by NH4Cl. Ammonium and sulphate ions had no inhibitory effects at these concentrations.Conclusions:Filament formation in NaCl-inhibited Z. mobilis is due entirely to the chloride ion, while the sodium ion has the major effect on growth and ethanol production.Significance and Impact of the Study:To avoid filamentous growth, chloride ions should be excluded from ethanol fermentations employing Z. mobilis, e.g. sulphuric is preferable to hydrochloric acid when hydrolysing lignocellulosic substrates prior to fermentation.

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