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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

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.

This article is dedicated to the memory of Tricia Mason.

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