AUTHOR=Boonmee Atsadang , Oliver Haley F. , Chaturongakul Soraya 

TITLE=Listeria monocytogenes 10403S Alternative Sigma-54 Factor σL Has a Negative Role on Survival Ability Under Bile Exposure

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.713383

DOI=10.3389/fmicb.2021.713383

ISSN=1664-302X

ABSTRACT=<p><italic>Listeria monocytogenes</italic> is a Gram-positive bacterium causing listeriosis in animals and humans. To initiate a foodborne infection, <italic>L. monocytogenes</italic> has to pass through the host gastrointestinal tract (GIT). In this study, we evaluated survival abilities of <italic>L. monocytogenes</italic> 10403S wild type (WT) and its isogenic mutants in alternative sigma (σ) factor genes (i.e., <italic>sigB</italic>, <italic>sigC</italic>, <italic>sigH</italic>, and <italic>sigL</italic>) under simulated gastric, duodenal, and bile fluids. Within 10min of exposures, only bile fluid was able to significantly reduce survival ability of <italic>L. monocytogenes</italic> WT by 2 logs CFU/ml. Loss of <italic>sigL</italic> showed the greatest bile resistance among 16 strains tested, <italic>p</italic>&lt;0.0001, (i.e., WT, four single alternative σ factor mutants, six double mutants, four triple mutants, and one quadruple mutant). To further investigate the role of σ<sup>L</sup> in bile response, RNA-seq was conducted to compare the transcriptional profiles among <italic>L. monocytogenes</italic> 10403S <italic>ΔBCH</italic> triple mutant (lacking <italic>sigB</italic>, <italic>sigC</italic>, and <italic>sigH</italic> genes; expressing housekeeping σ<sup>A</sup> and σ<sup>L</sup>) and <italic>ΔBCHL</italic> quadruple mutant (lacking all alternative sigma factor genes; expressing only σ<sup>A</sup>) strains under BHI and 1% bile conditions. A total of 216 and 176 differentially expressed genes (DEGs) were identified in BHI and bile, respectively. We confirmed that <italic>mpt</italic> operon was shown to be strongly activated by σ<sup>L</sup>. Interestingly, more than 80% of DEGs were found to be negatively regulated in the presence of σ<sup>L</sup>. This includes PrfA regulon and its mediated genes (i.e., <italic>hly</italic>, <italic>hpt</italic>, <italic>inlB</italic>, <italic>clpP</italic>, <italic>clpE</italic>, <italic>groL</italic>, and <italic>inlC</italic>) which were downregulated in response to bile in the presence of σ<sup>L</sup>. This result suggests the potential negative role of σ<sup>L</sup> on bile survival, and the roles of σ<sup>L</sup> and σ<sup>B</sup> might be in a seesaw model prior to host cell invasion.</p>