Two-Component-System Histidine Kinases Involved in Growth of Listeria monocytogenes EGD-e at Low Temperatures

Two-component systems (TCSs) aid bacteria in adapting to a wide variety of stress conditions. While the role of TCS response regulators in the cold tolerance of the psychrotrophic foodborne pathogen Listeria monocytogenes has been demonstrated previously, no comprehensive studies showing the role of TCS histidine kinases of L. monocytogenes at low temperature have been performed. We compared the expression levels of each histidine kinase-encoding gene of L. monocytogenes EGD-e in logarithmic growth phase at 3 degrees C and 37 degrees C, as well as the expression levels 30 min, 3 h, and 7 h after cold shock at 5 degrees C and preceding cold shock ( at 37 degrees C). We constructed a deletion mutation in each TCS histidine kinase gene, monitored the growth of the EGD-e wild-type and mutant strains at 3 degrees C and 37 degrees C, and measured the minimum growth temperature of each strain. Two genes, yycG and lisK, proved significant in regard to induced relative expression levels under cold conditions and cold-sensitive mutant phenotypes. Moreover, the Delta resE mutant showed a lower growth rate than that of wild-type EGD-e at 3 degrees C. Eleven other genes showed upregulated gene expression but revealed no cold-sensitive phenotypes. The results show that the histidine kinases encoded by yycG and lisK are important for the growth and adaptation of L. monocytogenes EGD-e at low temperature.