| Summary: | <p>Abstract</p> <p>Background</p> <p>Pathogens tolerate stress conditions that include low pH, oxidative stress, high salt and high temperature in order to survive inside and outside their hosts. Lipopolysaccharide (LPS), which forms the outer-leaflet of the outer membrane in Gram-negative bacteria, acts as a permeability barrier. The lipid A moiety of LPS anchors it to the outer membrane bilayer. The MsbB enzyme myristoylates the lipid A precursor and loss of this enzyme, in <it>Salmonella</it>, is correlated with reduced virulence and severe growth defects that can both be compensated with extragenic suppressor mutations.</p> <p>Results</p> <p>We report here that <it>msbB </it>(or <it>msbB somA</it>) <it>Salmonella </it>are highly sensitive to physiological CO<sub>2 </sub>(5%), resulting in a 3-log reduction in plating efficiency. Under these conditions, <it>msbB Salmonella </it>form long filaments, bulge and lyse. These bacteria are also sensitive to acidic pH and high osmolarity. Although CO<sub>2 </sub>acidifies LB broth media, buffering LB to pH 7.5 did not restore growth of <it>msbB </it>mutants in CO<sub>2</sub>, indicating that the CO<sub>2</sub>-induced growth defects are not due to the effect of CO<sub>2 </sub>on the pH of the media. A transposon insertion in the glucose metabolism gene <it>zwf </it>compensates for the CO<sub>2 </sub>sensitivity of <it>msbB Salmonella</it>. The <it>msbB zwf </it>mutants grow on agar, or in broth, in the presence of 5% CO<sub>2</sub>. In addition, <it>msbB zwf </it>strains show improved growth in low pH or high osmolarity media compared to the single <it>msbB </it>mutant.</p> <p>Conclusion</p> <p>These results demonstrate that <it>msbB </it>confers acute sensitivity to CO<sub>2</sub>, acidic pH, and high osmolarity. Disruption of <it>zwf </it>in <it>msbB </it>mutants restores growth in 5% CO<sub>2 </sub>and results in improved growth in acidic media or in media with high osmolarity. These results add to a growing list of phenotypes caused by <it>msbB </it>and mutations that suppress specific growth defects.</p>
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