Journal
FOOD MICROBIOLOGY
Volume 96, Issue -, Pages -Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.fm.2020.103722
Keywords
Shiga toxin-producing Escherichia coli (STEC); DNA adenine Methylase (Dam); Restriction and modification (R-M) systems; Epigenetic regulation; Methylome; Transcriptomics; Shiga toxin; Stx-prophages
Funding
- USDA-ARS CRIS project [5325-42000-050-00D, 5325-42000-051-00D, 5325-42000-049-00D]
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The study revealed significant differences in the methylome between different pathogenic strains of Escherichia coli, with one key reason being the presence of the PstI R-M system. In comparison to deficiency in DNA adenine methylase (Dam), deficiency in the PstI R-M system only had a transcriptional impact on a small number of genes.
We previously reported a distinct methylome between the two Shiga toxin-producing Escherichia coli (STEC) O145:H28 strains linked to the 2010 U.S. lettuce-associated outbreak (RM13514) and the 2007 Belgium ice cream-associated outbreak (RM13516), respectively. This difference was thought to be attributed to a prophage encoded type II restriction-modification system (PstI R-M) in RM13514. Here, we characterized this PstI R-M system in comparison to DNA adenine methylase (Dam), a highly conserved enzyme in gamma proteobacteria, by functional genomics. Deficiency in Dam led to a differential expression of over 1000 genes in RM13514, whereas deficiency in PstI R-M only impacted a few genes transcriptionally. Dam regulated genes involved in diverse functions, whereas PstI R-M regulated genes mostly encoding transporters and adhesins. Dam regulated a large number of genes located on prophages, pathogenicity islands, and plasmids, including Shiga toxin genes, type III secretion system (TTSS) genes, and enterohemolysin genes. Production of Stx2 in dam mutant was significantly higher than in RM13514, supporting a role of Dam in maintaining lysogeny of Stx2-prophage. However, following mitomycin C treatment, Stx2 in RM13514 was significantly higher than that of dam or PstI R-M deletion mutant, implying that both Dam and PstI R-M contributed to maximum Stx2 production.
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