Integration of the Salmonella Typhimurium methylome and transcriptome following environmental or metabolic perturbation reveals DNA methylation and transcriptional regulation are largely decoupled

Abstract

AbstractDespite being in a golden age of prokaryotic epigenomics, little work has systematically examined the plasticity and functional impacts of the bacterial DNA methylome. Here, we leveraged SMRT sequencing to examine the m6A DNA methylome of two Salmonella enterica ser. Typhimurium strains: 14028s and a ΔmetJ mutant with derepressed methionine metabolism, grown in Luria Broth or a media that simulates the intracellular environment. We find that the methylome is remarkably static—over 95% of adenosine bases retain their methylation status across conditions. Integration of methylation with transcriptomic data revealed no correlation between methylation and gene expression. Further, examining the transcriptome in ΔyhdJ bacteria, lacking the m6A methylase with the most dynamic methylation pattern in our dataset, revealed little evidence of YhdJ-mediated gene regulation. Curiously, despite G(m6A)TC motifs being particularly resistant to change across conditions, we found that the Dam methylase is required for the ΔmetJ motility defect. This ΔmetJ motility defect may be partially driven by hypermethylation of the chemotaxis gene tsr. Together, these data redefine the S. Typhimurium epigenome as a highly stable system that has rare, but important, roles in transcriptional regulation. Incorporating these lessons into future studies will be critical as we progress through the epigenomic era.