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J. Bacteriol. doi:10.1128/JB.01655-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Physiologic effects of forced down-regulation of dnaK and groEL expression in Streptococcus mutans

Department of Oral Biology, University of Florida College of Dentistry, Gainesville, Florida 32610-0424

^* To whom correspondence should be addressed. Email: rburne{at}dental.ufl.edu.

	Abstract

Strains of Streptococcus mutans lacking DnaK or GroEL appear not to be isolable. To better distinguish the roles played by these chaperones/chaperonins in the physiology of S. mutans, we created a knock-down strategy to lower the levels of DnaK by over 95% in strain SM12 and the level of GroEL about 80% in strain SM13. Interestingly, GroEL levels were approximately two-fold higher in SM12 than in the parent strain, but the levels of DnaK were not altered in the GroEL knock-down strain. Both SM12 and SM13 grew slower than the parent strain, had a strong tendency to aggregate in broth culture and showed major changes in their proteomes. Compared with the wild-type strain, SM12 and SM13 had impaired biofilm-forming capacity when grown in the presence of glucose. The SM12 strain was impaired in its capacity to grow at 44°C or at pH 5.0 and was more susceptible to H₂O₂, whereas SM13 behaved like the wild-type strain under these conditions. Phenotypical reversions were noted for both mutants when cells were grown in continuous culture at low pH, suggesting the occurrence of compensatory mutations. These results demonstrate that DnaK and GroEL differentially affect expression of key virulence traits, including biofilm formation and acid tolerance, and support that these chaperones have evolved to accommodate unique roles in the context of this organism and its niche.

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