Overexpression of lpxT Gene in Escherichia coli Inhibits Cell Division and Causes Envelope Defects without Changing the Overall Phosphorylation Level of Lipid A

Overexpression of lpxT Gene in Escherichia coli Inhibits Cell Division and Causes Envelope Defects without Changing the Overall Phosphorylation Level of Lipid A

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LpxT is an inner membrane protein that transfers a phosphate group from the essential lipid undecaprenyl pyrophosphate (C-55PP) to the lipid A moiety of lipopolysaccharide, generating a lipid A tris-phosphorylated species.The protein is encoded by the non-essential lpxT gene, which is conserved in distantly related Gram-negative bacteria.In this work, we investigated the phenotypic effect of lpxT ectopic expression from a plasmid in Escherichia coli.

We found 5 that lpxT induction inhibited cell division and led to the formation of elongated cells, mostly with absent or altered septa.Moreover, the cells became sensitive to detergents and to hypo-osmotic shock, indicating that they had cell envelope defects.These effects were not due to lipid A hyperphosphorylation or C-55PP sequestering, but most likely to defective lipopolysaccharide transport.

Indeed, lpxT overexpression in mutants lacking the L,D-transpeptidase LdtD and Hair Removal LdtE, which protect cells with outer membrane defects from osmotic lysis, caused cell envelope defects.Moreover, we found that pyrophosphorylated lipid A was also produced in a lpxT deletion mutant, indicating that LpxT is not the only protein able to perform such lipid A modification in E.coli.