kdsA mutations affect FtsZ-ring formation in Escherichia coli K-12

No one has, as yet, addressed the relationship between the nature of the outer membrane and cell division. kdsA encodes 3-deoxy-D-manno-octulosonic acid (KDO) 8-phosphate synthetase which catalyses the first step in the synthesis of KDO, the linker between lipid A and oligosaccharide of lipopolysaccharide (LIPS). Seven temperature-sensitive mutants containing missense mutations in kdsA were affected in the production of KDO and all mutants stopped dividing at 41 degreesC and formed filaments with either one or no FtsZ ring. All observed defects were reversed by the plasmid-borne wild-type kdsA gene. Western blotting analysis, however, demonstrated that the amount of FtsZ protein was not affected by the mutation. The mutants were more susceptible to various hydrophobic materials, such as novobiocin, eosin Y and SDS at 36 degreesC. Methylene blue, however, restored kdsA mutant growth. Plasmid-borne wildtype msbA, encoding a lipid A transporter in the ABC family, partially suppressed kdsA mutation. A mutation of IpxA, functioning at the first stage in lipid A biosynthesis, inhibited both cell division and growth, producing short filaments. These results indicate that the instability of the outer membrane, caused by the defect in KDO biosynthesis, affects FtsZ-ring formation.