Open AccessThe sigma factor RpoN (σ54) is involved in osmotolerance in Listeria monocytogenes
Author(s) -
Okada Yumiko,
Okada Nobuhiko,
Makino Souichi,
Asakura Hiroshi,
Yamamoto Shigeki,
Igimi Shizunobu
Publication year - 2006
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.2006.00405.x
Subject(s) - rpon , sigma factor , mutant , betaine , osmotic concentration , listeria monocytogenes , osmotic pressure , biology , carnitine , biochemistry , osmotic shock , microbiology and biotechnology , gene expression , gene , genetics , bacteria , promoter
Listeria monocytogenes is able to grow under conditions of high osmolarity. We constructed a deletion mutant of rpoN , encoding the alternative sigma factor RpoN, and analyzed its response to osmotic stress. In a minimal medium with 4% NaCl and 1 mM betaine, the mutant showed a similar growth to that of the parental strain, EGD. In the same medium with 4% NaCl and 1 M carnitine, the growth rate of the mutant was greatly reduced, when the optical density at 600 nm (OD 600 ) at the starting point of growth, was 0.15. However, when growth of the culture was started at an OD 600 of 0.025, the growth of the mutant was similar to that of EGD. The mutant's expression of two betaine transporter genes, betL and gbuB , and the carnitine transporter gene opuCA , was osmotically induced at a level similar to EGD, and its rate of carnitine uptake was similar to that of EGD. These results suggest that the growth defect from the rpoN mutant is caused not by the transcriptional regulation of opuCA or by a decrease in carnitine uptake, but possibly by larger amounts of carnitine being needed for growth of the mutant in minimal medium when NaCl is present.