Prokaryotic DNA methylation and its functional roles

DNA methylation is known as a universal mechanism of epigenetic regulation in all kingdoms of life. Particularly, given that prokaryotes lack key elements such as histones and nucleosomes that can structurally modify DNA, DNA methylation is considered a major epigenetic regulator in these organisms. However, because DNA methylation studies have focused primarily on eukaryotes, the mechanism of prokaryotic DNA methylation has been less studied than in eukaryotes. DNA methylation in prokaryotes plays an important role in regulating not only the host defense system, but also the cell cycle, gene expression, and virulence that can respond directly to the environment. Recent advances in sequencing techniques capable of detecting methylation signals have allowed for the characterization of prokaryotic genome-wide epigenetic regulation. In this review, we describe representative examples of cellular events regulated by DNA methylation in prokaryotes, from early studies to current applications.