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Plasmid-influenced changes in Mycobacterium avium catalase activity
1Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg 24061.
Abstract:
A virulent Mycobacterium avium strain, LR25, which carries three plasmids (18, 28, and 165 kilobases) and grows at 43 degrees C was compared with its plasmid-free, avirulent segregant, strain LR163, to identify the basis for the latter's inability to grow at 43 degrees C. The failure of mid-log-phase cultures of strain LR163 to grow at 43 degrees C was dependent on the presence of high levels of culture aeration. In addition, highly aerated cultures of strain LR163 failed to grow at 37 degrees C. Mid-log-phase cultures of strain LR163 had 30% of the catalase activity of strain LR25 and were more hydrogen peroxide (0.08%, wt/vol) susceptible. Catalase activity of strain LR25 was higher in cultures grown with high aeration than in those grown with almost no aeration. These data support the contention that plasmid-encoded genes influence M. avium catalase activity.
Insights
Mycobacterium avium plasmids influence catalase activity and growth at high temperatures. Plasmid-free strains show reduced catalase and are sensitive to aeration, impacting thermotolerance.
Area of Science:
- Microbiology
- Genetics
Background:
- Virulent Mycobacterium avium strain LR25 possesses three plasmids and thermotolerance.
- Avirulent, plasmid-free segregant strain LR163 lacks thermotolerance.
- Investigating the role of plasmids in M. avium virulence and growth characteristics.
Purpose of the Study:
- To determine the genetic basis for the avirulent strain LR163's inability to grow at 43°C.
- To elucidate the role of plasmids in Mycobacterium avium thermotolerance and catalase activity.
Main Methods:
- Comparative analysis of virulent (LR25) and avirulent (LR163) M. avium strains.
- Growth curve analysis under varying aeration conditions (high vs. low).
- Measurement of catalase activity and susceptibility to hydrogen peroxide.
Main Results:
- Strain LR163 failed to grow at 43°C, dependent on high culture aeration.
- Highly aerated cultures of LR163 also failed to grow at 37°C.
- LR163 exhibited 30% of LR25's catalase activity and increased hydrogen peroxide susceptibility.
- LR25's catalase activity was higher under high aeration.
Conclusions:
- Plasmid-encoded genes in M. avium significantly influence catalase activity.
- Reduced catalase activity and altered aeration sensitivity contribute to the avirulence and thermotolerance defect in plasmid-free strains.