CO2- and anaerobiosis-induced changes in physiology and gene expression of different Listeria monocytogenes strains

Although carbon dioxide (CO2) is known to inhibit growth of most bacteria, very little is known about the cellular response. The food-borne pathogen Listeria monocytogenes is characterized by its ability to grow in high CO2 concentrations at refrigeration temperatures. We examined the listerial responses of different strains to growth in air, 100% N-2, and 100% CO2. The CO2-induced changes in membrane lipid fatty acid composition and expression of selected genes were strain dependent. The acid-tolerant L. monocytogenes LO28 responded in the same manner to CO2 as to other anaerobic, slightly acidic environments (100% N-2, pH 5.7). An increase in the expression of the genes encoding glutamate decarboxylase (essential for survival in strong acid) as well as an increased amount of branched-chain fatty acids in the membrane was observed in both atmospheres. In contrast, the acid-sensitive L. monocytogenes strain EGD responded differently to CO2 and N-2 at the same pH. In a separate experiment with L. monocytogenes 412, an increased isocitrate dehydrogenase activity level was observed for cells grown in CO2-containing atmospheres. Together, our findings demonstrate that the CO2-response is a partly strain-dependent complex mechanism. The possible links between the CO2-dependent changes in isocitrate dehydrogenase activity, glutamate metabolism and branched fatty acid biosynthesis are discussed.