To Modulate Survival under Secondary Stress Conditions, Listeria monocytogenes 10403S Employs RsbX To Downregulate σ ^B Activity in the Poststress Recovery Stage or Stationary Phase

Abstract

Listeria monocytogenes is a saprophytic bacterium that thrives in diverse environments and causes listeriosis via ingestion of contaminated food. RsbX, a putative sigma B ( B ) regulator, is thought to maintain the ready state in the absence of stress and reset the bacterium to the initial state in the poststress stage in Bacillus subtilis. We wondered whether RsbX is functional in L. monocytogenes under different stress scenarios. Genetic deletion and complementation of the rsbX gene were combined with survival tests and transcriptional and translational analyses of B expression in response to stresses. We found that deletion of rsbX increased survival under secondary stress following recovery of growth after primary stress or following stationary-phase culturing. The ⌬rsbX mutant had higher expression of B than its parent strain in the recovery stage following primary sodium stress and in stationary-phase cultures. Apparently, increased B expression had contributed to improved survival in the absence of RsbX. There were no significant differences in survival rates or B expression levels in response to primary stresses between the rsbX mutant and its parent strain during the exponential phase. Therefore, we provide clear evidence that RsbX is a negative regulator of L. monocytogenes B during the recovery period after a primary stress or in the stationary phase, thus affecting its survival under secondary stress. Listeria monocytogenes causes listeriosis in humans, mostly due to consumption of contaminated foods. As a saprophytic bacterium thriving in diverse environments, L. monocytogenes can survive and grow over a wide range of environmental conditions, including temperatures from Ϫ0.4 to 45°C, pH as low as 2.5, and high osmolarity (10% to 20% NaCl) (1-4). The general stressresponsive alternative sigma factor sigma B ( B ), which was first identified in Bacillus subtilis (5), plays a pivotal role in its resistance to environmental stresses (6, 7).B is coexpressed with seven of its principal regulators (regulators of sigma B rsbR, rsbS, rsbT, rsbU, rsbV, rsbW, and rsbX) in B. subtilis (8) and L. monocytogenes (9-11). Partner switching upon phosphorylation and dephosphorylation is the main regulatory mechanism of this protein cluster in response to stresses. This has been studied mostly in B. subtilis (12)(13)(14) and seldom in L. monocytogenes. In unstressed B. subtilis, RsbW sequesters B into an association that prevents it from interacting with RNA polymerase. RsbV is dephosphorylated by RsbU or RsbP in response to environmental or metabolic stress, respectively (15, 16). The dephosphorylated RsbV is capable of competing for RsbW, resulting in B liberation. The upstream proteins RsbT, RsbS, and RsbR form a complex called the "stressosome" in B. subtilis (17)(18)(19). Environmental stresses stimulate the kinase activity of RsbT, which can then be released from the stressosome available to activate RsbU (20).However, the interactions of these regulatory proteins in L. monocytogenes under stresses are not well...

The σB signalling activation pathway in the enteropathogen Clostridioides difficile

“…In B. subtilis and L. monocytogenes , rsbX , which clusters with sigB , encodes a PP2C phosphatase responsible for resetting the stressosome involved in the detection of environmental stresses activating σ B (Marles‐Wright et al, ; Marles‐Wright and Lewis, ). This reset restricts the positive feedback loop and enables the σ B signalling pathway to return to its initial state, avoiding toxicity due to an excess of active σ B (Voelker et al, ; Xia et al, ). The absence of a positive feedback loop on the transcription of the sigB operon in C. difficile limiting its expression might explain the absence of any RsbX homologue in this bacterium.…”

Transcriptional response of Bacillus megaterium FDU301 to PEG200-mediated arid stress

“…Studies on the mechanisms of bacterial arid tolerance have mostly been on food-borne pathogens (for example Salmonella (23), Listeria monocytogenes (38,39), Staphylococcus aureus (26) and Streptococcus pneumoniae (40)) and soil bacteria (Pseudomonas (13) and Rhizobiaceae (41)). The transcriptomic response to arid conditions has not been well studied in Bacillus.…”

Stress responses of Listeria monocytogenes

“…Sigma B (δ B ) is a positive regulator of some general and cold stress response genes including fri, oppA, opuCA and ltrC (10). It is stated that alternative sigma factors δ C , δ H , δ L along with δ B are related to regulate cold adaptation processing of bacteria (10,44,59).…”