Phenotypic and transcriptomic analyses of Sigma L-dependent characteristics in Listeria monocytogenes EGD-e

In this study the phenotypic and transcriptomic traits associated with the alternative sigma factor protein Sigma L in Listeria monocytogenes EGD-e were investigated. It was demonstrated that Sigma L is required for efficient growth in presence of stress associated with food preservative measures such as low temperature and organic acids. Furthermore, besides attenuation of swarming motility, the disruption of Sigma L in this bacterium also reduces resistance to a diverse range of toxic compounds, including some of the antibiotics used in listeriosis treatment. Genes under Sigma L-dependent transcriptional regulation were identified based on comparison of transcriptomes between exponentially growing cells of the EGD-e sigL null mutant and its parental strain cultivated under cold stress (3 °C) and optimized (37 °C) temperature conditions. Four hundred and forty genes under positive Sigma L-dependent transcriptional regulation were identified. The Sigma L regulon as revealed under these conditions comprises genes that code for proteins with diverse cellular functions including protein synthesis, nutrient transport, energy metabolism, cell envelope synthesis, and motility. The diverse range of transcriptome alterations induced by a sigL null mutation is thus consistent with the multiple phenotypic defects observed in the EGD-e ΔsigL mutant. These results demonstrate that Sigma L provides important global transcription regulatory functions in L. monocytogenes EGD-e. These promote execution of various cellular processes and stress adaptation responses thereby enabling this bacterium to overcome various food preservation measures as well as antibiotics and other toxic chemicals.