DNA-methylating activity of mycobacteria

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Mycobacterium species are known for diverse metabolic capabilities.
• DNA methylation is a crucial epigenetic modification in prokaryotes, influencing gene expression and genome stability.
• Understanding methylating enzymes in mycobacteria is important for their biology and potential biotechnological applications.

Purpose of the Study:

• To investigate and characterize the in vitro methylating activity of four distinct Mycobacterium strains.
• To identify the specific DNA bases methylated by these mycobacterial enzymes.
• To compare the methylation efficiency of mycobacterial DNA by homologous enzymes versus phage DNA.

Main Methods:

• In vitro enzymatic assays using cell extracts from Mycobacterium phlei, Mycobacterium smegmatis strain Butyricum, Mycobacterium smegmatis strain Rabinowitz, and lysogenic Mycobacterium smegmatis strain Rabinowitz.
• Analysis of methylated DNA bases using chromatographic and sequencing techniques.
• Kinetic analysis of methylation reactions to assess enzyme activity and nuclease contamination.

Main Results:

• All four studied Mycobacterium strains demonstrated in vitro methylating activity.
• Enzyme extracts from M. smegmatis strain Butyricum and M. phlei exhibited stronger methylating activity compared to M. smegmatis strain Rabinowitz and its lysogenic counterpart.
• The methylases from all strains methylated adenine and cytosine residues in acceptor DNA, producing 5-methylcytosine and 6-methylaminopurine.
• Mycobacterial DNAs showed only 25-30% methylation by their corresponding methylases in vitro, mirroring low in vivo methylation levels.
• Methylation kinetics suggested a low non-specific nuclease content in the mycobacterium cells.

Conclusions:

• The studied Mycobacterium strains possess active DNA methylases capable of modifying adenine and cytosine.
• Variations in methylating activity exist among the strains, with M. phlei and M. smegmatis strain Butyricum showing higher potency.
• The low methylation efficiency of mycobacterial DNA by homologous methylases is consistent with observed in vivo patterns, suggesting specific regulatory mechanisms or substrate preferences.