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J Bacteriol, September 1998, p. 4547-4554, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Identification of the Gene Encoding the Alternative Sigma Factor sigma B from Listeria monocytogenes and Its Role in Osmotolerancedagger

Lynne A. Becker, Mehmet Sevket Çetin, Robert W. Hutkins, and Andrew K. Benson*

Department of Food Science and Technology, University of Nebraska, Lincoln, Nebraska 68583-0919

Received 4 May 1998/Accepted 6 July 1998

Listeria monocytogenes is well known for its robust physiology, which permits growth at low temperatures under conditions of high osmolarity and low pH. Although studies have provided insight into the mechanisms used by L. monocytogenes to allay the physiological consequences of these adverse environments, little is known about how these responses are coordinated. In the studies presented here, we have cloned the sigB gene and several rsb genes from L. monocytogenes, encoding homologs of the alternative sigma factor sigma B and the RsbUVWX proteins, which govern transcription of a general stress regulon in the related bacterium Bacillus subtilis. The L. monocytogenes and B. subtilis sigB and rsb genes are similar in sequence and physical organization; however, we observed that the activity of sigma B in L. monocytogenes was uniquely responsive to osmotic upshifting, temperature downshifting, and the presence of EDTA in the growth medium. The magnitude of the response was greatest after an osmotic upshift, suggesting a role for sigma B in coordinating osmotic responses in L. monocytogenes. A null mutation in the sigB gene led to substantial defects in the ability of L. monocytogenes to use betaine and carnitine as osmoprotectants. Subsequent measurements of betaine transport confirmed that the absence of sigma B reduced the ability of the cells to accumulate betaine. Thus, sigma B coordinates responses to a variety of physical and chemical signals, and its function facilitates the growth of L. monocytogenes under conditions of high osmotic strength.

* Corresponding author. Mailing address: Department of Food Science and Technology, 358 Food Industry Complex, University of Nebraska, Lincoln, NE 68583-0919. Phone: (402) 472-5637. Fax: (402) 472-1693. E-mail: abenson{at}foodsci.unl.edu.

dagger Journal Series paper 12219 of the Nebraska Agricultural Experimental Station.

J Bacteriol, September 1998, p. 4547-4554, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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