Virulence attenuation of two Mas-like polyketide synthase mutants of Mycobacterium tuberculosis

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Pathogenic mycobacteria possess a unique cell envelope rich in methyl-branched fatty acids.
• These complex lipids are crucial for cell envelope structure and the virulence of Mycobacterium tuberculosis.
• Previous work identified the polyketide synthase Mas involved in mycocerosic acid synthesis.

Purpose of the Study:

• To investigate the role of mas-like polyketide genes (pks5 and pks7) in the synthesis of complex fatty acids.
• To determine the impact of disrupting pks5 and pks7 on the cell envelope composition and virulence of M. tuberculosis.
• To elucidate the origin and pathogenic relevance of these unique fatty acids.

Main Methods:

• Genetic disruption of pks5 and pks7 genes in M. tuberculosis.
• Analysis of fatty acid composition in mutant strains.
• Assessment of virulence and growth defects in a mouse model.

Main Results:

• Disruption of pks7 led to a deficiency in phthiocerol dimycocerosate production.
• The pks5 mutant's cell envelope composition was indistinguishable from the wild-type M. tuberculosis H37Rv.
• Both pks5 and pks7 mutants exhibited significant growth defects in vivo (in mice).

Conclusions:

• The pks7 gene is essential for the synthesis of phthiocerol dimycocerosates in M. tuberculosis.
• While pks5 does not appear to affect cell envelope composition, both pks5 and pks7 are critical for full virulence in a mouse model.
• These findings highlight the importance of specific methyl-branched fatty acids and their biosynthetic pathways in mycobacterial pathogenesis.