Glycerol uptake in Escherichia coli is sensitive to membrane lipid composition

In Escherichia coli, a functional GlpF protein is necessary for efficient uptake of glycerol at low concentrations. Here we show that GlpF-mediated glycerol uptake was sensitive to a variety of lipid alterations. Overproduction or mutation of the genes coding for enzymes involved in lipid biosynthesis resulted in changed membrane composition and fluidity. The strains with altered lipid composition had a substrate affinity for glycerol (Km) similar to that of wild-type cells, but the Vmax for glycerol uptake was affected. Experiments with glpF::lacZ and glpK::lacZ protein fusions showed that the expression of these two genes was not changed under these conditions. In addition, we observed that mutations in glpF were accompanied by reduced membrane permeability for compounds unrelated to glycerol. Passive diffusion across the membranes of glpF mutants for o-nitrophenyl galactoside was 5-fold slower than in glpF+ cells. The mutants were more resistant to the hydrophobic antibiotic tetracycline, as well as to the membrane perturbants ethanol and dimethylsulphoxide and to the stress of low-osmolarity medium.