Investigating the role of FOF1 ATPase in Zymomonas mobilis through deletion of its FO and F1 subcomplexes.

Zymomonas mobilis has a typical FOF1 ATPase, yet does not exhibit oxidative phosphorylation. In order to investigate the function of the ATPase we sought to delete the FO and the F1 subcomplexes, respectively. Clean mutants could be obtained after selection under aerobic conditions. Growth analysis of the mutants showed that they strictly require oxygen for growth and that the oxygen supply is a factor determining maximal growth rate. This is contrary to the wild type, which grows fastest under anaerobic conditions. In the mutant strains, ethanol remains the main catabolic product; however glucose consumption rates are reduced, and the mutants show a higher sensitivity to low medium pH. Compared to the wild type, the mutants show an increased biomass yield. Our data support the previously proposed regulatory role of the FOF1 ATPase in controlling glycolytic flux, and indicate that the FOF1 ATPase plays an important role in expelling protons from the cytoplasm. In the mutants, this function is taken over by the electron transport chain in the presence of oxygen.