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Genetic separation of serum opacity factor from M protein of group A streptococci
Abstract:
Mutagenized cultures of three strains of group A streptococci which were M positive and produced the extracellular serum opacity factor (OF) were screened for mutants which failed to exhibit OF activity on serum agar plates. All cell fractions from three mutants studied in detail, including culture supernatants, protoplast membranes, and cytoplasmic fractions, were completely devoid of activity. Two OF- isolates also lacked OF antigen, whereas the third continued to produce cross-reacting antigen. All three mutants were resistant to phagocytosis and yielded acid-extractable M antigen, indicating that the M protein of each strain was unaltered by the mutations. The separation of the OF+ and M+ phenotypes by mutation establishes that genes which code for the M protein and OF are distinct; therefore, the activities and antigenic determinants of each must be associated with separate, distinct protein molecules.
Insights
Mutant group A streptococci lacking serum opacity factor (OF) were identified. These mutants confirm that OF and M protein are distinct molecules, coded by separate genes.
Area of Science:
- Microbiology
- Bacteriology
- Molecular Biology
Background:
- Group A Streptococcus (GAS) possesses M protein, crucial for virulence and resistance to phagocytosis.
- Extracellular serum opacity factor (OF) is another GAS virulence factor, but its relationship with M protein is unclear.
Purpose of the Study:
- To investigate the genetic relationship between M protein and OF production in GAS.
- To determine if M protein and OF are encoded by distinct genes.
Main Methods:
- Mutagenesis of M-positive, OF-positive GAS strains.
- Screening for mutants lacking OF activity.
- Analysis of cell fractions (supernatants, membranes, cytoplasmic) for OF activity.
- Assessment of M antigen presence and OF antigenicity in mutants.
- Phagocytosis resistance assays.
Main Results:
- Mutants lacking OF activity were successfully generated.
- OF activity and antigen were absent in two mutants; one retained cross-reacting antigen.
- All three mutants remained M-positive and resistant to phagocytosis.
- M protein was present and functional in all mutants, unaffected by the OF-negative mutation.
Conclusions:
- The M protein and OF are distinct molecules, not directly linked.
- Genes encoding M protein and OF are separate, confirming distinct genetic control.
- This separation implies unique protein molecules responsible for M and OF activities and antigenicity.