Transmission electron micrographs of wild-type and Δcj0256 (inset) Campylobacter jejuni cells. Image courtesy of M. S. Trent, The University of Texas, Austin, USA.

Post-translational modification of cell surface factors is known to be important for the virulence of many bacterial pathogens, including Campylobacter jejuni, a major worldwide cause of bacterial diarrhoea. Now, Cullen and Trent describe the identification of a phosphoethanolamine transferase that modifies components of the flagella and lipo-oligosaccharide in the C. jejuni periplasm, linking outer-membrane biogenesis and cell motility.

The cell surface features of C. jejuni are subjected to a range of post-translational modifications. One previously characterized surface modification of Gram-negative bacteria involves the remodelling of the lipid A component of lipo-oligosaccharide, resulting in protection against cationic antimicrobial peptides (AMPs). However, lipid A modifications had not been characterized in C. jejuni. To address this, Cullen and Trent carried out a bioinformatic search of the C. jejuni genome using as a comparison a previously characterized lipid A phosphoethanolamine transferase from Helicobacter pylori that is necessary for AMP resistance, and they identified the cj0256 gene as a putative homologue. The authors expressed Cj0256 in Escherichia coli str. K12 substr. W3110 and then radiolabelled cells with inorganic [³²P]phosphate. Thin-layer chromatography of lipid A species purified from this strain revealed that expression of Cj0256 resulted in modification of lipid A with phosphoethanolamine. Deletion of cj0256 in C. jejuni caused a block in this modification of lipid A, which led to a striking decrease in resistance to the AMP polymyxin B. Lipid A modification and AMP resistance could be restored by complementing the deletion strain with either cj0256 or eptA, the gene encoding the E. coli phosphoethanolamine transferase.

Interestingly, cj0256 had been identified previously in a screen for genes involved in cell motility and has been shown to interact directly with the flagellar rod protein FlgG. Consistent with this, in strains lacking cj0256 the authors observed a decrease in motility of ∼ 50%, and transmission electron microscopy revealed that ∼ 95% of these cells lacked flagella. Radiolabelling experiments coupled with mass spectrometry revealed that FlgG is modified with phosphoethanolamine and that this modification is dependent on Cj0256. Importantly, although complementation with eptA was able to rescue phosphoethanolamine modification of lipid A in the absence of cj0256, it was not able to support phosphoethanolamine modification of FlgG.

These findings indicate that cj0256 encodes a phosphoethanolamine transferase that is involved in post-translational modification of both protein and lipid components at the cell surface. They also suggest that two key mechanisms that are important for C. jejuni virulence are jointly regulated, such that resistance to host AMPs and the adherence to (and invasion of) host epithelial cells depend on Cj0256 to transfer phosphoethanolamine to lipid A and FlgG, respectively. Therefore, targeting Cj0256 might prove to be an effective strategy for treating C. jejuni infections.

Author: Andrew Jermy - Copyright © 2010 Nature Publishing Group, a division of MacMillan Publishers Limited; used with permission