Multigenerational Proteolytic Inactivation of Restriction Upon Subtle Genomic Hypomethylation
In Pseudomonas aeruginosa, restriction inactivation upon growth at high temperatures was previously described, however, which system is being inactivated, the underlying mechanism, as well as the timing of recovery, remain unknown. Here, we report that P. aeruginosa Type I methyltransferase (HsdMS) and restriction endonuclease (HsdR) components are degraded by two Lon-like proteases when replicating above 41 °C, which induces partial genome hypomethylation and simultaneously prevents self-targeting, respectively. Interestingly, upon return to 37 °C, methyltransferase activity returns gradually, with restriction activity not fully recovering for over 60 bacterial generations, representing the longest bacterial memory to our knowledge. Forced expression of HsdR over the first 45 generations is toxic, demonstrating the fitness benefit of HsdR inactivation. Overall design: 6mA modification sequencing for  Pseudomonas aeruginosa samples.