Experimental Evolution Reveals Redox State Modulates Mycobacterial Pathogenicity

Area of Science:

• Microbiology
• Evolutionary Biology
• Pathogenesis

Background:

• Understanding Mycobacterium tuberculosis pathogenesis and vaccine development requires insights into its evolution as a pathogen.
• Investigating evolutionary adaptations to clinical stressors like hydrogen peroxide (H2O2) can reveal mechanisms of increased bacterial pathogenicity.

Purpose of the Study:

• To explore how adaptation to H2O2 stress in Mycobacterium smegmatis mc251 leads to genetic mutations and enhanced pathogenicity.
• To compare the physiological and genetic responses of M. smegmatis strains and relate them to virulence differences observed in M. tuberculosis.

Main Methods:

• Whole-genome sequencing to identify genetic mutations.
• Utilizing a Wayne dormancy model to assess bacterial recovery and growth.
• Analyzing gene expression (katG), ATP levels, and redox-related protein (Rv1996) phenotypes.

Main Results:

• A mutation in the fur gene of M. smegmatis mc251 led to increased katG expression and enhanced recovery from dormancy.
• M. smegmatis mc251 exhibited a growth advantage under anaerobic dormancy recovery and had low ATP levels, indicating reduced respiration.
• Differential phenotypes of Rv1996 were observed across various Mycobacterium species and strains, linked to specific redox states.

Conclusions:

• The same gene can exhibit different phenotypes under varying physiological conditions, influencing pathogenicity.
• Differences in redox states may explain why M. smegmatis is nonpathogenic while M. tuberculosis is pathogenic, despite similar virulence factors.
• M. smegmatis mc251, with improved characteristics, shows potential as a vaccine vector.