Respiration-deficient mutant (RDM) strains of Zymomonas mobilis were isolated from antibiotic-resistant mutants. These RPM strains showed various degrees of respiratory deficiency. All RDM strains exhibited much higher ethanol fermentation capacity than the wild-type strain under aerobic conditions. The strains also gained thermotolerance and exhibited greater ethanol production at high temperature (39 degrees C), under both non-aerobic and aerobic conditions, compared with the wild-type strain. Microarray and subsequent quantitative PCR analyses suggest that enhanced gene expression involved in the metabolism of glucose to ethanol resulted in the high ethanol production of RDM strains under aerobic growth conditions. Reduction of intracellular oxidative stress may also result in improved ethanol fermentation by RPM strains at high temperatures. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.