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Surface hydrophobicity, adherence, and aggregation of cell surface protein antigen mutants of Streptococcus mutans
T Koga1, N Okahashi, I Takahashi
1Department of Dental Research, National Institute of Health, Tokyo, Japan.
Abstract:
The pac gene of the serotype c strain Streptococcus mutans MT8148 encodes a cell surface protein antigen (PAc) of approximate 190 kilodaltons. The serotype c strain S. mutans GS-5 does not produce the 190-kilodalton PAc but produces a lower-molecular-weight protein that reacts with anti-PAc serum. The SphI-BamHI fragment of the pac gene was ligated with the S. mutans-Escherichia coli shuttle vector pSA3. The chimeric shuttle vector was transformed into strain GS-5, and two transformants (TK15 and TK18) were isolated. These transformants produced a large amount of cell-free and cell-bound PAc of 190 kilodaltons. No plasmid was isolated from these transformants, and the EcoRI fragments of their chromosomal DNA hybridized with the erythromycin resistance gene in the shuttle vector DNA, indicating insertion of the chimeric shuttle vector DNA into the chromosomal DNA. The cell hydrophobicity of strains TK15 and TK18 as well as PAc-defective mutants constructed by inserting an erythromycin resistance gene into the pac gene of strain MT8148 was analyzed. Strains MT8148, TK15, and TK18 were hydrophobic. On the other hand, strain GS-5 and PAc-defective MT8148 transformants were hydrophilic. Resting cells of the hydrophobic strains attached in larger numbers to saliva-coated hydroxyapatite than did the hydrophilic strains. Human whole saliva induced the aggregation of cells of the hydrophobic strains but not that of cells of the hydrophilic strains. These results suggest that cell surface PAc of S. mutans serotype c participates in attachment of the streptococcal cell to experimental pellicles.
Insights
The cell surface protein antigen (PAc) of Streptococcus mutans serotype c is crucial for bacterial attachment to teeth. Introducing the PAc gene into a non-producing strain restored hydrophobicity and enhanced pellicle binding.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Streptococcus mutans is a primary cause of dental caries.
- The cell surface protein antigen (PAc) in serotype c S. mutans is implicated in adhesion.
- Understanding PAc's role is vital for developing anti-caries strategies.
Purpose of the Study:
- To investigate the function of the PAc gene in Streptococcus mutans serotype c.
- To determine the role of PAc in bacterial cell surface properties and attachment.
- To analyze the impact of PAc expression on Streptococcus mutans hydrophobicity and pellicle interaction.
Main Methods:
- Cloning the pac gene from S. mutans MT8148 into a shuttle vector.
- Transforming the vector into a PAc-deficient S. mutans GS-5 strain.
- Assessing cell hydrophobicity, attachment to hydroxyapatite, and saliva-induced aggregation.
Main Results:
- Transformed S. mutans GS-5 (strains TK15 and TK18) expressed 190 kDa PAc and exhibited increased hydrophobicity.
- PAc-defective mutants of S. mutans MT8148 became hydrophilic.
- Hydrophobic strains showed greater attachment to saliva-coated hydroxyapatite and cell aggregation compared to hydrophilic strains.
Conclusions:
- Cell surface PAc of S. mutans serotype c significantly influences bacterial hydrophobicity.
- PAc plays a critical role in the attachment of S. mutans to experimental pellicles.
- These findings highlight PAc as a potential target for preventing dental caries.