(p)ppGpp buffers cell division when membrane fluidity decreases in
Escherichia coli.
Abstract
Fluidity is an inherent property of biological membranes and its
maintenance (homeoviscous adaptation) is important for optimal
functioning of membrane-associated processes. The fluidity of bacterial
cytoplasmic membrane increases with temperature or an increase in the
proportion of unsaturated fatty acids and vice versa. We found
strains deficient in the synthesis of guanine nucleotide analogues
(p)ppGpp and lacking FadR, a transcription factor involved in fatty acid
metabolism exhibited growth defect that was rescued by an increase in
growth temperature or unsaturated fatty acid content. The strain lacking
(p)ppGpp was sensitive to genetic or chemical perturbations that
decrease the proportion of unsaturated fatty acids over saturated fatty
acids. Microscopy showed the growth defect was associated with cell
filamentation and lysis and rescued by combined expression of cell
division genes ftsQ, ftsA and ftsZ from plasmid.
The results implicate (p)ppGpp in the positive regulation of cell
division during loss of membrane fluidity. To our knowledge, this is the
first report of a (p)ppGpp mediated regulation needed for adaptation to
membrane fluidity loss in bacteria.