Evidence for an evolutionary antagonism between Mrr and Type III modification systems.

Area of Science:

• Bacteriology
• Molecular Biology
• Genetics

Background:

• Mrr protein from Escherichia coli is a Type IV restriction endonuclease targeting methylated DNA.
• Mrr activity is induced by high-pressure stress in E. coli MG1655 without causing toxicity.
• The interaction between Mrr and other bacterial systems is not fully understood.

Purpose of the Study:

• Investigate the genotoxicity of E. coli Mrr protein when expressed in Salmonella typhimurium LT2.
• Identify the genetic factors in S. typhimurium LT2 responsible for Mrr-induced genotoxicity.
• Explore the evolutionary relationship between Mrr and Type III restriction-modification systems.

Main Methods:

• Genetic screening to identify factors contributing to Mrr genotoxicity.
• Expression analysis of Mrr and Type III restriction-modification system components.
• Bioinformatic analysis of genome databases for correlating Mrr and Mod gene distribution.

Main Results:

• E. coli Mrr protein causes significant genotoxicity in S. typhimurium LT2.
• The endogenous Type III restriction-modification system (StyLTI) of S. typhimurium LT2 is solely responsible for Mrr-induced toxicity.
• Expression of the S. typhimurium LT2 mod gene activates Mrr activity in E. coli MG1655.
• Horizontal acquisition of the mrr locus correlates with the loss of Mod functionality in other bacterial species.
• An anti-correlation exists between Mrr and Mod homologues in bacterial genomes.

Conclusions:

• The Mrr protein's genotoxicity in S. typhimurium is dependent on the presence of the Type III restriction-modification system.
• An evolutionary antagonism exists between Mrr and Mod systems, potentially involving defense against foreign epigenetic regulation.