Physiologic Effects of Forced Down-Regulation of dnaK and groEL Expression in Streptococcus mutans

University of Florida, Gainesville, Florida, United States
Journal of Bacteriology (Impact Factor: 2.81). 04/2007; 189(5):1582-8. DOI: 10.1128/JB.01655-06
Source: PubMed


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 knockdown 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 twofold higher in SM12 than in the parent strain, but the levels
of DnaK were not altered in the GroEL knockdown 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 capacities 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 a low pH, suggesting the occurrence of compensatory mutations. These results
demonstrate that DnaK and GroEL differentially affect the 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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    • "In addition, S. mutans-encoded GroEL and DnaK act as negative regulators of surface protein antigen C (PAc), which has an important role in the interaction between bacterial cells and acquired pellicles on the tooth surface (Ishibashi et al., 2010). Moreover, S. agalactiae-encoded GroEL and DnaK differentially regulate the expression of key streptococcal virulence factors, including those involved in the formation of biofilms and acid tolerance (Lemos et al., 2007). The serine protease ClpP plays a key role in the regulation of bacterial growth and increases bacterial survival under stress conditions, particularly heat-shock conditions in S. agalactiae (Nair et al., 2003) and S. mutans (Lemos and Burne, 2002). "
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    ABSTRACT: Streptococci cause a variety of diseases, such as dental caries, pharyngitis, meningitis, pneumonia, bacteremia, endocarditis, erysipelas, and necrotizing fasciitis. The natural niche of this genus of bacteria ranges from the mouth and nasopharynx to the skin, indicating that the bacteria will inevitably be subjected to environmental changes during invasion into the host, where it is exposed to the host immune system. Thus, the Streptococcus−host interaction determines whether bacteria are cleared by the host’s defenses or whether they survive after invasion to cause serious disease. If this interaction were to be deciphered, it could aid in the development of novel preventive and therapeutic agents. Streptococcus species possess many virulent factors, such as peroxidases and heat-shock proteins (HSPs), which play key roles in protecting the bacteria from hostile host environments. This review will discuss insights into the mechanism(s) by which streptococci adapt to host environments. Additionally, we will address how streptococcal infections trigger host stress responses; however, the mechanism by which bacterial components modulate host stress responses remains largely unknown.
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    • "It is remarkable that among the differentially expressed proteins between the mutant and the wild type strain, some have been previously characterized as involved in biofilm formation in X. citri or in other pathogenic bacteria. Such is the case of DNA-directed RNA polymerase subunit β [32], tryptophan synthase [43], GroEL [44,45], FadL [32,42,46] and several TBDTs [42,47]. Interestingly, high intracellular L-tryptophan concentration prevents biofilm formation and triggers degradation of mature biofilm in E. coli[43]. "
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    • "DnaK is central in the molecular chaperone complex that includes DnaK, DnaJ and GrpE. In addition to its role in protein folding and in protecting cells from stress, DnaK plays a central role in induction of capsule (Genevaux et al., 2001) and also in expression of genes related to pathogenicity and virulence (Hanawa et al., 2002; Lemos et al., 2007). It has been shown in mice to be an important surface streptococcal virulence factor and protective antigen (Lemos et al., 2000; Fluegge et al., 2004; Kim et al., 2006). "
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