Growth of Zymomonas mobilis ZM4 in media containing sodium acetate was inhibited above 12 g sodium acetate/l at pH 5.0. Following mutagenesis of ZM4, an acetate-tolerant strain was isolated in continuous culture that grew in the presence of 20 g sodium acetate/l at pH 5.0. In continuous culture with complete cell recycle at 30 degrees C and pH 5.4 using media containing 110 g glucose/l, the maintenance energy coefficient (m) for the mutant was found to increase from 1.9 g glucose/g cell dry wt. h at 12 g sodium acetate/l up to 3.9 g/g. h at 20 g/l.