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Mutational loss of sensitivity to mutacin GS-5 in Streptococcus pyogenes: characterization of a mutant deficient in
Abstract:
By means of a stepwise selection procedure, mutants capable of growing in the presence of relatively high multiplicities of a bacteriocin from Streptococcus mutans GS-5 were obtained from a sensitivie strain of Streptococcus pyogenes. Mutacin-neutralizing activity of cell extracts containing receptor protein was examined in one variant that adsorbed 1/6 the amount of bacteriocin adsorbed by the parent strain under conditions equivalent to "saturation." Partially purified receptor protein from both parent and mutant cells neutralized an equivalent amount of bacteriocin on a weight-to-weight basis, indicating that in vitro there was no significant difference in affinity for the mutacin between the respective receptor fractions. Cell extracts from the mutant, solubilized by treatment with trichloroacetic acid, neither neutralized mutacin activity nor interfered with receptor protein-mediated mutacin neutralization in vitro. The mutant phenotype may thus represent a cell surface density of receptor protein which results in the adsorption of sublethal amounts of mutacin. The mutant retained its sensitivity to other mutacins, e.g., those produced by strains LM-7 and BHT of S. mutans, and did not differ from wild-type cells with respect to either detergent sensitivity (sodium lauryl sulfate and Triton X-100) or to inhibition by penicillin, rifampin, bacitracin, erythromycin, and tetracycline.
Insights
Researchers developed Streptococcus pyogenes mutants resistant to a Streptococcus mutans bacteriocin. This resistance is linked to reduced bacteriocin adsorption, not altered receptor affinity, suggesting a lower density of surface receptors.
Area of Science:
- Microbiology
- Bacteriology
- Molecular Biology
Background:
- Bacteriocins, such as mutacin from Streptococcus mutans, are antimicrobial peptides.
- Bacteriocin resistance in bacteria can arise from modifications in target receptors or neutralizing mechanisms.
- Streptococcus pyogenes is a human pathogen that can be targeted by bacteriocins.
Purpose of the Study:
- To obtain and characterize Streptococcus pyogenes mutants resistant to a specific bacteriocin (mutacin) from Streptococcus mutans.
- To investigate the mechanism of bacteriocin resistance in the selected mutants.
- To determine if resistance is due to altered receptor binding or other factors.
Main Methods:
- Stepwise selection of Streptococcus pyogenes mutants resistant to Streptococcus mutans bacteriocin.
- Measurement of bacteriocin adsorption by parent and mutant strains.
- Examination of mutacin-neutralizing activity in cell extracts and partially purified receptor proteins.
- In vitro assays to assess receptor-mediated neutralization and interference.
Main Results:
- Mutants resistant to Streptococcus mutans bacteriocin were successfully isolated.
- Resistant mutants adsorbed significantly less bacteriocin compared to the parent strain.
- Partially purified receptor proteins from both parent and mutant strains showed equivalent bacteriocin-neutralizing activity on a weight-to-weight basis.
- Solubilized cell extracts from mutants did not neutralize bacteriocin or interfere with receptor-mediated neutralization.
Conclusions:
- The observed bacteriocin resistance in Streptococcus pyogenes mutants is likely due to a reduced density of surface receptors for the bacteriocin.
- This reduced receptor density leads to the adsorption of sublethal amounts of bacteriocin.
- The affinity of the receptor protein for the bacteriocin remains unchanged in the resistant mutants.