Intercellular mosaic methylation in fast-growing Mycobacterium tuberculosis clinical isolates

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Orphan DNA adenine methyltransferases (MTases) in Mycobacterium tuberculosis (Mtb) display genetic diversity.
• Recent observations revealed anomalous hypomethylation by Type I MTase MamC in wild-type mamC isolates, termed 'MamC-anomalous'.

Purpose of the Study:

• To investigate the mechanisms behind anomalous hypomethylation by MamC in Mtb.
• To understand the relationship between MamC DNA methylation and bacterial growth dynamics.

Main Methods:

• Heterogeneity analysis to detect intercellular mosaic methylation (IMM).
• Analysis of chromosome copy number variation as a proxy for bacterial growth rate.
• Assessment of MamC methylation efficiency across the replication axis on both DNA strands.

Main Results:

• MamC-anomalous isolates exhibit intercellular mosaic methylation (IMM), a novel finding for prokaryotic Type I MTases.
• A stable difference in chromosome copy number was observed in MamC-anomalous isolates, suggesting a distinct growth phase.
• MamC methylation efficiency decreased with distance from the origin of replication, exaggerated in MamC-anomalous isolates, unlike MamA and MamB.

Conclusions:

• MamC DNA methylation in Mtb is uniquely associated with bacterial growth dynamics.
• Intercellular mosaic methylation (IMM) is a newly identified phenomenon in prokaryotic Type I MTases.
• MamC methylation patterns are distinct from other Mtb MTases (MamA, MamB) and are influenced by growth phases.