Genes encoding putative DEAD-box RNA helicases in Listeria monocytogenes EGD-e are needed for growth and motility at 3°C

Quantitative RT-PCR revealed that transcripts of all four putative DEAD-box RNA helicase genes of the psychrotrophic pathogen Listeria monocytogenes EGD-e are found at higher levels in organisms grown at 3 degrees C than at 37 degrees C. At 3 degrees C, growth of the three corresponding gene deletion mutants Delta lmo0866, Delta lmo1450 and Delta lmo1722 was clearly restricted. The minimum growth temperatures of the three mutants were also higher than that of the wild-type EGD-e. In addition to inability to grow at 3 degrees C, growth of Delta lmo0866 and Delta lmo1722 was reduced at 25 degrees C, suggesting special roles of Lmo0866 and Lmo1722 in growth at suboptimal temperatures. Growth of Delta lmo1450 was restricted not only at 3 degrees C and 25 degrees C, but also at 37 degrees C, suggesting that Lmo1450 plays a universal role in growth of L. monocytogenes EGD-e. Moreover, cold-sensitive Delta lmo0866, Delta lmo1450 and Delta lmo1722 were impaired in motility. The Delta lmo0866 and Delta lmo1450 strains were non-motile, while Delta lmo1722 showed reduced motility. This study shows that the putative DEAD-box RNA helicase genes lmo0866, lmo1450 and lmo1722 are necessary for cold tolerance and motility of L. monocytogenes EGD-e.