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

Zymomonas mobilis has a typical F O F 1 ATPase, yet does not exhibit oxidative phosphorylation. In order to investigate the function of the ATPase we sought to delete the F O and the F 1 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 F O F 1 ATPase in controlling glycolytic flux, and indicate that the F O F 1 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.