PmrD is Required for Modifications to Escherichia Coli Endotoxin that Promote Antimicrobial Resistance
OSTP Journal Article
University of Texas at Austin Austin United States
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In Salmonella enterica, PmrD is a connector protein that links the two-component systems PhoP-PhoQ and PmrA-PmrB. While Escherichia coli encodes a PmrD homolog, it is thought to be incapable of connecting PhoPQ and PmrAB in this organism due to functional divergence from the S. enterica protein. However, our laboratory previously observed that low concentrations of Mg2, a PhoPQ-activating signal, leads to the induction of PmrAB-dependent lipid A modifications in wild-type E. coli C. M. Herrera, J. V. Hankins, and M. S. Trent, Mol Microbiol 7614441460, 2010, httpdx.doi.org10.1111j.1365-2958.2010.07150.x. These modifications include hosphoethanolamine pEtN and 4-amino-4-deoxy-L-arabinose L-Ara4N, which promote bacterial resistance to cationic antimicrobial peptides CAMPs when affixed to lipid A. Here, we demonstrate that pmrD is required for modification of the lipid A domain of E. coli lipopolysaccharide LPS under low-Mg2 growth conditions. Further, RNA sequencing shows that E. coli pmrD influences the expression of pmrA and its downstream targets, including genes coding for the modification enzymes that transfer pEtN and L-Ara4N to the lipid A molecule. In line with these findings, a pmrD mutant is dramatically impaired in survival compared with the wild-type strain when exposed to the CAMP polymyxin B. Notably, we also reveal the presence of an unknown factor or system capable of activating pmrD to promote lipid A modification in the absence of the PhoPQ system. These results illuminate a more complex network of protein interactions surrounding activation of PhoPQ and PmrAB in E. coli than previously understood.