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Applied and Environmental Microbiology, June 2006, p. 3955-3959, Vol. 72, No. 6
0099-2240/06/$08.00+0     doi:10.1128/AEM.02607-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

A Cold-Sensitive Listeria monocytogenes Mutant Has a Transposon Insertion in a Gene Encoding a Putative Membrane Protein and Shows Altered (p)ppGpp Levels

Siqing Liu,¹ Darrell O. Bayles,² Tricia M. Mason,³ and Brian J. Wilkinson^3*

Bioproducts and Biocatalysis Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, Peoria, Illinois,¹ Microbial Food Safety Research Unit, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Wyndmoor, Pennsylvania,² Microbiology Group, Department of Biological Sciences, Illinois State University, Normal, Illinois³

Received 4 November 2005/ Accepted 23 March 2006

A cold-sensitive Listeria monocytogenes mutant designated cld-14 was obtained by transposon Tn917 mutagenesis. The gene interrupted by Tn917 in cld-14 was the L. monocytogenes LMOf2365_1485 homolog, which exhibits 45.7% homology to the Bacillus subtilis yqfF locus. LMOf2365_1485, here designated pgpH, encodes a putative integral membrane protein with a predicted molecular mass of 81 kDa. PgpH is predicted to contain a conserved N-terminal signal peptide sequence, seven transmembrane helices, and a hydrophilic C terminus, which likely extends into the cytosol. The Tn917 insertion in pgpH is predicted to result in production of a premature polypeptide truncated at the fifth transmembrane domain. The C terminus of PgpH, which is probably absent in cld-14, contains a highly conserved HD domain that belongs to a metal-dependent phosphohydrolase family. Strain cld-14 accumulated higher levels of (p)ppGpp than the wild type accumulated, indicating that the function of PgpH may be to adjust cellular (p)ppGpp levels during low-temperature growth. The cld-14pgpH⁺ complemented strain was able to grow at a low temperature, like the parent strain, providing direct evidence that the activity of PgpH is important in low-temperature adaptation. Because of its predicted membrane location, PgpH may play a critical role in sensing the environmental temperature and altering cellular (p)ppGpp levels to allow the organism to adapt to low temperatures.

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* Corresponding author. Mailing address: Microbiology Group, Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120. Phone: (309) 438-7244. Fax: (309) 438-3722. E-mail: bjwilkin{at}ilstu.edu.

This article is dedicated to the memory of Tricia Mason.

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Applied and Environmental Microbiology, June 2006, p. 3955-3959, Vol. 72, No. 6
0099-2240/06/$08.00+0     doi:10.1128/AEM.02607-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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