Effects of organic buffers on batch fermentations of Zymomonas mobilis in a synthetic and complex medium

Abstract

The influence of organic buffers, pH, and medium composition were compared on Zymomonas mobilis cell concentration, fermentation time, specific growth rates and ethanol production rates in batch fermentations. The fermentations conducted at pH 6.0 required less time than fermentations at pH 5.0. The synthetic medium (containing inorganic nitrogen and Ca-pantothenate) fermentations had a lower specific growth rate of 0.2 h −1 compared to 0.2–0.5 h −1 for the complex medium (containing yeast extract) fermentations. The cell yield from the synthetic medium fermentations were reduced by 20–35% compared to complex medium fermentations. A 0.02 M succinate/succinic acid buffer added to the medium to control the pH had minimal effect on the fermentation kinetics. Adding acetic acid/acetate buffer to the medium slightly increased the specific productivity and decreased cell yield by 20–75% over a range of concentrations. An ethanol yield of 0.47 g g −1 was obtained regardless of the medium composition.