Cyclopropane fatty acids improve Escherichia coli survival in acidified minimal media by reducing membrane permeability to H+ and enhanced ability to extrude H+

The physiological role of cyclopropane fatty acids (CFAs) in acid stress resistance was studied by in situ microelectrode H+ flux measurements of Escherichia coli Frag1 and its isogenic CFA-deficient mutant JBM 1. After exposure to pH 4 for 16 h, net H+ influx in JBM 1 was twice that of the parent strain. H+ flux stabilisation at pH 6 after acid stress took more time in the cfa− mutant. The data suggest increased proton permeability and decreased ability to extrude H+ in the absence of CFA, and they support the hypothesis that CFAs protect E. coli in acidic environments by decreasing membrane permeability to H+.