The role of the alternative sigma factor, sigma(B), in osmotic response and regulation of stress response in Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen that is particularly problematic for the food industry due to its robust physiology and capability of handling adverse environmental conditions. Although much is known about its physiology, little is known how L. monocytogenes orchestrates the mechanisms to subvert the harmful effects of environmental stress. In the related organism, Bacillus subtilis, the alternative sigma factor, σB is known to control and direct transcription of over hundred genes involved in the general stress response and their products are necessary for promoting growth and survival under adverse conditions. The objective of this research was to determine whether the alternative sigma factor, σB, contributes to the adaptive physiology and osmotolerance of L. monocytogenes.; Our initial works showed that σB is present in L. monocytogenes along with four-gene operon that regulates its activity. Subsequent completion of the genome sequence showed that four additional genes are present upstream in an operon. Primer extension analyses indicated that various types of stress, including elevated osmolarity and high and low temperature shifts, induce σB activity in L. monocytogenes. Loss of σB resulted in reduced growth rates in high osmolarity media and impaired accumulation of the compatible solutes, betaine and carnitine. We further characterized the regulatory role of σB in compatible solute accumulation and the control of betaine and carnitine transporters in L. monocytogenes.