msbB deletion confers acute sensitivity to CO2 in Salmonella enterica serovar Typhimurium that can be suppressed by a loss-of-function mutation in zwf

We report here that msbB (or msbB somA) Salmonella are highly sensitive to physiological CO2 (5%), resulting in a 3-log reduction in plating efficiency. Under these conditions, msbB Salmonella form long filaments, bulge and lyse. These bacteria are also sensitive to acidic pH and high osmolarity. Although CO2 acidifies LB broth media, buffering LB to pH 7.5 did not restore growth of msbB mutants in CO2, indicating that the CO2-induced growth defects are not due to the effect of CO2 on the pH of the media. A transposon insertion in the glucose metabolism gene zwf compensates for the CO2 sensitivity of msbB Salmonella. The msbB zwf mutants grow on agar, or in broth, in the presence of 5% CO2. In addition, msbB zwf strains show improved growth in low pH or high osmolarity media compared to the single msbB mutant.These results demonstrate that msbB confers acute sensitivity to CO2, acidic pH, and high osmolarity. Disruption of zwf in msbB mutants restores growth in 5% CO2 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 msbB and mutations that suppress specific growth defects.Lipopolysaccharide (LPS), the most abundant molecule on the surface of Gram-negative bacteria, acts as a permeability barrier and renders the outer-leaflet of the outer membrane (OM) relatively impermeable to hydrophobic antibiotics, detergents [1], and host complement [2]. LPS consists of three major components: lipid A, core polysaccharides and O-linked polysaccharides. Lipid A, with its fatty acid anchors [lauric, myristic and sometimes palmitic acid], is an endotoxin primarily responsible for TNFα-mediated septic shock. The addition of myristic acid to the lipid A precursor is catalyzed by the enzyme MsbB [3].It has been shown that msbB Salmonella serovar Typhimurium exhibits severe growth defects in LB and sensitivity to bile salts (MacConkey) and EGTA-containing media. However, compensatory suppressor