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

Liu, Siqing, Bayles, Darrell O., Mason, Tricia M., Wilkinson, Brian J.
Applied and environmental microbiology 2006 v.72 no.6 pp. 3955
Listeria monocytogenes, mutants, phenotype, cold tolerance, genes, bacterial proteins, membrane proteins, transposons, mutagenesis, guanosine, hydrolases, cold, adaptation, food pathogens
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.