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Phosphatidylinositol is an essential phospholipid of mycobacteria
M Jackson1, D C Crick, P J Brennan
1Department of Microbiology, Colorado State University, Fort Collins, Colorado 80523, USA.
Abstract:
Phosphatidylinositol (PI) and metabolically derived products such as the phosphatidylinositol mannosides and linear and mature branched lipomannan and lipoarabinomannan are prominent phospholipids/lipoglycans of Mycobacterium sp. believed to play important roles in the structure and physiology of the bacterium as well as during host infection. To determine if PI is an essential phospholipid of mycobacteria, we identified the pgsA gene of Mycobacterium tuberculosis encoding the phosphatidylinositol synthase enzyme and constructed a pgsA conditional mutant of Mycobacterium smegmatis. The ability of this mutant to synthesize phosphatidylinositol synthase and subsequently PI was dependent on the presence of a functional copy of the pgsA gene carried on a thermosensitive plasmid. The mutant grew like the control strain under permissive conditions (30 degrees C), but ceased growing when placed at 42 degrees C, a temperature at which the rescue plasmid is lost. Loss of cell viability at 42 degrees C was observed when PI and phosphatidylinositol dimannoside contents dropped to approximately 30 and 50% of the wild-type levels, respectively. This work provides the first evidence of the essentiality of PI to the survival of mycobacteria. PI synthase is thus an essential enzyme of Mycobacterium that shows promise as a drug target for anti-tuberculosis therapy.
Insights
Phosphatidylinositol (PI) is essential for Mycobacterium survival. Disrupting PI synthesis halts bacterial growth, indicating PI synthase is a promising drug target for tuberculosis therapy.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Phospholipids like phosphatidylinositol (PI) and derived lipoglycans are key components of Mycobacterium species.
- These molecules are crucial for bacterial structure, physiology, and host infection processes.
Purpose of the Study:
- To investigate whether phosphatidylinositol (PI) is an essential phospholipid for mycobacterial survival.
- To identify the phosphatidylinositol synthase (PgsA) gene and its role in PI synthesis.
Main Methods:
- Identified the pgsA gene in Mycobacterium tuberculosis.
- Constructed a conditional pgsA mutant in Mycobacterium smegmatis.
- Utilized a thermosensitive plasmid for conditional gene expression and mutant analysis.
Main Results:
- The pgsA mutant's growth and PI synthesis were dependent on the pgsA gene.
- Growth arrest occurred at 42°C due to loss of the rescue plasmid and subsequent PI depletion.
- Loss of cell viability correlated with significant reductions in PI and phosphatidylinositol dimannoside levels.
Conclusions:
- This study provides the first evidence that phosphatidylinositol (PI) is essential for mycobacterial survival.
- PI synthase is a validated essential enzyme in Mycobacterium species.
- PI synthase represents a potential drug target for developing novel anti-tuberculosis therapies.