Occurrence, evolution, and functions of DNA phosphorothioate epigenetics in bacteria

Tong Tong, Si Chen, Lianrong Wang, You Tang, Jae Yong Ryu, Susu Jiang, Xiaolin Wu, Chao Chen, Jie Luo, Zixin Deng, Zhiqiang Li, Sang Yup Lee, Shi Chen

The chemical diversity of physiological DNA modifications has expanded with the identification of phosphorothioate (PT) modification in which the nonbridging oxygen in the sugar-phosphate backbone of DNA is replaced by sulfur. Together with DndFGH as cognate restriction enzymes, DNA PT modification, which is catalyzed by the DndABCDE proteins, functions as a bacterial restriction-modification (R-M) system that protects cells against invading foreign DNA. However, the occurrence ofdndsystems across a large number of bacterial genomes and their functions other than R-M are poorly understood. Here, a genomic survey revealed the prevalence of bacterialdndsystems: 1,349 bacterialdndsystems were observed to occur sporadically across diverse phylogenetic groups, and nearly half of these occur in the form of a solitarydndBCDEgene cluster that lacks thedndFGHrestriction counterparts. A phylogenetic analysis of 734 complete PT R-M pairs revealed the coevolution of M and R components, despite the observation that several PT R-M pairs appeared to be assembled from M and R parts acquired from distantly related organisms. Concurrent epigenomic analysis, transcriptome analysis, and metabolome characterization showed that a solitary PT modification contributed to the overall cellular redox state, the loss of which perturbed the cellular redox balance and inducedPseudomonas fluorescensto reconfigure its metabolism to fend off oxidative stress. An in vitro transcriptional assay revealed altered transcriptional efficiency in the presence of PT DNA modification, implicating its function in epigenetic regulation. These data suggest the versatility of PT in addition to its involvement in R-M protection.