The sigma factor RpoN (sigma54) is involved in osmotolerance in Listeria monocytogenes.
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 (OD600) at the starting point of growth, was 0.15. However, when growth of the culture was started at an OD600 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.
Okada
Yumiko
Y
Division of Biomedical Food Research, National Instutute of Health Sciences, Tokyo 158-8501, Japan. yokada@nihs.go.jp
Okada
Nobuhiko
N
Makino
Sou-ichi
S
Asakura
Hiroshi
H
Yamamoto
Shigeki
S
Igimi
Shizunobu
S
D001426:Bacterial Proteins / Q000235:genetics; D001622:Betaine / Q000378:metabolism; D002331:Carnitine / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics; D003470:Culture Media; D017353:Gene Deletion; D016680:Genome, Bacterial; D005998:Glycine / Q000378:metabolism; D008089:Listeria monocytogenes / Q000235:genetics* / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000235:genetics; D009154:Mutation; D027701:Organic Cation Transport Proteins / Q000235:genetics; D009994:Osmolar Concentration; D051877:RNA Polymerase Sigma 54 / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000378:metabolism
D001426:Bacterial Proteins; C119698:BetL protein, Listeria monocytogenes; D002352:Carrier Proteins; D003470:Culture Media; D026901:Membrane Transport Proteins; D027701:Organic Cation Transport Proteins; C401955:glycine betaine transporter, Listeria monocytogenes; C492021:opuC protein, Listeria monocytogenes; D001622:Betaine; D012965:Sodium Chloride; D051877:RNA Polymerase Sigma 54; D002331:Carnitine; D005998:Glycine