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Infection and Immunity, February 2006, p. 1243-1254, Vol. 74, No. 2
0019-9567/06/$08.00+0     doi:10.1128/IAI.74.2.1243-1254.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Polynucleotide Phosphorylase Negatively Controls spv Virulence Gene Expression in Salmonella enterica

Microbiology and Tumor Biology Center, Karolinska Institute, Nobels väg 16, 171 77 Stockholm, Sweden,¹ Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, United Kingdom,² Centre for Molecular Biology and Infection, Department of Infectious Diseases, Imperial College London, Armstrong Road, London SW7 2AZ, United Kingdom,³ Molecular Microbiology Group, Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, United Kingdom⁴

Received 1 August 2005/ Returned for modification 12 September 2005/ Accepted 2 October 2005

Mutational inactivation of the cold-shock-associated exoribonuclease polynucleotide phosphorylase (PNPase; encoded by the pnp gene) in Salmonella enterica serovar Typhimurium was previously shown to enable the bacteria to cause chronic infection and to affect the bacterial replication in BALB/c mice (M. O. Clements et al., Proc. Natl. Acad. Sci. USA 99:8784-8789, 2002). Here, we report that PNPase deficiency results in increased expression of Salmonella plasmid virulence (spv) genes under in vitro growth conditions that allow induction of spv expression. Furthermore, whole-genome microarray-based transcriptome analyses of bacteria growing inside murine macrophage-like J774.A.1 cells revealed six genes as being significantly up-regulated in the PNPase-deficient background, which included spvABC, rtcB, entC, and STM2236. Mutational inactivation of the spvR regulator diminished the increased expression of spv observed in the pnp mutant background, implying that PNPase acts upstream of or at the level of SpvR. Finally, competition experiments revealed that the growth advantage of the pnp mutant in BALB/c mice was dependent on spvR as well. Combined, our results support the idea that in S. enterica PNPase, apart from being a regulator of the cold shock response, also functions in tuning the expression of virulence genes and bacterial fitness during infection.

Editor: D. L. Burns

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