Comparative sequence analysis revealed altered chromosomal organization and a novel insertion sequence encoding DNA modification and potentially stress-related functions in an Escherichia coli O157:H7 foodborne isolate

Authors: Sharma, Vijay; Akavaram, Surya Tej; SCHAUT, ROBERT - Orise Fellow

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/22/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: We recently described the complete genome of enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain NADC 6564, an isolate of strain 86-24 linked to the 1986 disease outbreak. In the current study, we compared the chromosomal sequence of NADC 6564 to the well-characterized chromosomal sequences of EHEC O157:H7 strains EDL933 and Sakai in order to identify differences in chromosomal organization and determine the presence or absence of specific sequences indicative directly or indirectly of differential host or environmental adaptability of NADC 6564. The comparative analysis revealed that the NADC 6564 chromosome (5466 kbp) was 32 kb and 81 kb smaller than Sakai (5498 kbp) and EDL933 (5547 kbp) chromosomes, respectively. Aligned chromosomal sequences of these strains contained identical Linear Conserved Blocks (LCB) but some of these LCBs had undergone rearrangement in NADC 6564. All three strains contained 18 bacteriophage-like elements at similar chromosomal sites except that NADC 6564 contained an additional phage-like element in a 33 kb DNA segment flanked by direct repeats. The 33 kb region contained genes encoding integrases, transposases, a transcriptional regulator, a DNA binding protein, an adhesion, and a phosphoethanolamine (PEA) transferase. The PEA gene showed 32-33 percent homology (nucleotide and amino acid) to four other PEA transferase-encoding genes present in the chromosome of NADC 6564 and other EHEC strains, but greater than 95 percent homology to a PEA transferase-encoding gene of uropathogenic and avian pathogenic E. coli and EHEC O104:H21. The five PEA genes of NADC 6564 showed varying degrees of homology to mcr1 and mcr2 encoding colistin resistance. Although NADC 6564 showed higher minimum inhibitory concentration for colistin compared to EDL933 and Sakai harboring four PEA genes in their chromosomes, NADC 6564 remained colistin-sensitive. The 33 kb region also contained two oppositely transcribed operons encoding for DNA backbone S-modification via phosphorothioation and DNA restriction pathways, respectively. These operons conferred S-modification on DNA, which has been linked to enhanced bacterial tolerance to oxidative stressors. In summary, the altered physical organization of the conserved regions of NADC 6564 chromosome could be attributed to recombination events and the acquisition of genes for DNA S-modification could potentially enhance NADC 6564 adaptability to host and/or environment under conditions of oxidative stress as has been demonstrated for bacterial strains capable of S-modification of DNA.