The effect of methylation on some biological parameters in Salmonella enterica serovar Typhimurium

Cell growth is tightly coupled to DNA replication and its methylation [Proc Natl Acad Sci U S A 93 (1996) 12206-12211]. In a culture medium, growing of Salmonella Typhimurium (S. Typhimurium) mutant cells (dam⁻) decreased (2.5 fold) relative to the wild type strain (dam⁺). In this study, we show that the reason for this growth deficiency is due to the DNA methylation. The absence of a Dam methyltransferase protein results in poor growth efficiency and disturbs the synchrony of replication initiation in vivo, as evaluated by flow cytometry. On the other hand, we show that lack of methylation could increase the DNA response to thermal stress (decreasing the DNA melting temperature, T(m)), and the reason for this effect is due to the methylation status and not to the number of guanine and cytosine bases (G+C) in the duplex DNA. Our results show that methylation is an epigenetic factor that may play a key role in the cell growth, the synchrony of DNA replication [C R Biologies 330 (2007) 576-580] and the stress protection.