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Applied and Environmental Microbiology, September 1999, p. 4040-4048, Vol. 65, No. 9
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Identification of an ATP-Driven, Osmoregulated Glycine Betaine Transport System in Listeria monocytogenes

Rinkei Ko1,dagger and Linda Tombras Smith2,*

Departments of Food Science and Technology1 and Agronomy and Range Science,2 University of California, Davis, Davis, California 95616

Received 11 February 1999/Accepted 7 July 1999

The ability of the gram-positive, food-borne pathogen Listeria monocytogenes to tolerate environments of elevated osmolarity and reduced temperature is due in part to the transport and accumulation of the osmolyte glycine betaine. Previously we showed that glycine betaine transport was the result of Na+-glycine betaine symport. In this report, we identify a second glycine betaine transporter from L. monocytogenes which is osmotically activated but does not require a high concentration of Na+ for activity. By using a pool of Tn917-LTV3 mutants, a salt- and chill-sensitive mutant which was also found to be impaired in its ability to transport glycine betaine was isolated. DNA sequence analysis of the region flanking the site of transposon insertion revealed three open reading frames homologous to opuA from Bacillus subtilis and proU from Escherichia coli, both of which encode glycine betaine transport systems that belong to the superfamily of ATP-dependent transporters. The three open reading frames are closely spaced, suggesting that they are arranged in an operon. Moreover, a region upstream from the first reading frame was found to be homologous to the promoter regions of both opuA and proU. One unusual feature not shared with these other two systems is that the start codons for two of the open reading frames in L. monocytogenes appear to be TTG. That glycine betaine uptake is nearly eliminated in the mutant strain when it is assayed in the absence of Na+ is an indication that only the ATP-dependent transporter and the Na+-glycine betaine symporter occur in L. monocytogenes.

* Corresponding author. Mailing address: Department of Agronomy and Range Science, University of California, Davis, Davis, CA 95616-8515. Phone: (530) 752-6161. Fax: (530) 752-4361. E-mail: lsmith{at}ucdavis.edu.

dagger Present address: Laboratory of Molecular Entomology and Baculovirology, The Institute of Physical and Chemical Research, Wako, Saitama, Japan.

Applied and Environmental Microbiology, September 1999, p. 4040-4048, Vol. 65, No. 9
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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