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Infection and Immunity, August 2004, p. 4579-4588, Vol. 72, No. 8
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.8.4579-4588.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

phgABC, a Three-Gene Operon Required for Growth of Streptococcus pneumoniae in Hyperosmotic Medium and In Vivo

Centre for Respiratory Research, Department of Medicine, Royal Free and University College Medical School, Rayne Institute, London WC1E 6JJ,¹ Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, United Kingdom²

Received 5 January 2004/ Returned for modification 11 February 2004/ Accepted 15 April 2004

To cause disease, bacterial pathogens need to be able to adapt to the physiological conditions found within the host, including an osmolality of approximately 290 mosmol kg^–1. While investigating Streptococcus pneumoniae genes contained within pneumococcal pathogenicity island 1, we identified a three-gene operon of unknown function termed phgABC. PhgC has a domain with similarity to diacylglycerol kinases of eukaryotes and is the first described member of a family of related proteins found in many gram-positive bacteria. phgA and phgC mutant strains were constructed by insertional duplication mutagenesis and found to have impaired growth under conditions of high osmotic and oxidative stress. The compatible solutes proline and glycine betaine improved growth of the wild-type and the phgA mutant strains in hyperosmolar medium, and when analyzed by electron microscopy, the cellular morphology of the phgA mutant strain was unaffected by osmotic stress. The phgA and phgC mutant strains were reduced in virulence in models of both systemic and pulmonary infection. As the virulence of the phgA mutant strain was not restored in gp91phox^–/– mice and the phgA and phgC mutant strains had reduced growth in both blood and serum, the reduced virulence of these strains is unlikely to be due to increased sensitivity to the respiratory burst of phagocytes but is, instead, due to impaired growth at physiological osmolality.

Editor: J. N. Weiser

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