Analysis of two B/O plasmids, R805a from 1972 and pCERC6 from 2008, reveals extensive mosaicism in B/O plasmid backbones

Publication date: Available online 27 February 2019Source: PlasmidAuthor(s): Robert A. Moran, Isabella A. Richardson, Ruth M. HallAbstractTwo B/O plasmids were sequenced. The kanamycin resistance plasmid R805a was found in a Salmonella Typhi strain from a 1972 typhoid fever outbreak in Mexico City. pCERC6, which confers resistance to ampicillin, streptomycin and sulphamethoxazole, was found in a commensal E. coli isolated from a healthy adult in Sydney in 2008. Both plasmids contain the same gene for RNAI, the incompatibility determinant, as the reference B/O plasmid pMU707 and the recently reported plasmid p838B-R, which came from a commensal E. coli isolated in Sydney in 2004. However, three different repA alleles are associated with the IncB/O rnaI. Whereas the repA gene of p838B-R is identical to that of pMU707, R805a and pCERC6 each carry a different repA. Comparison of the plasmid backbones revealed that R805a has a different oriT-nikAB region to that in pCERC6 and p838B-R, encoding different NikA relaxosome accessory factors and NikB relaxases. The different nikA genes were associated with oriT sites that differed in the sequences of their long, imperfect inverted repeats. A further 11 publicly available complete plasmid sequences contain the same B/O rnaI, with either the repA of pMU707/p838B-R or of R805a, and the oriT-nikAB region of p838B-R/pCERC6 or of R805a. All four possible combinations were seen. Extensive variation was also observed in the traY-excA entry exc...

Source: Plasmid - February 28, 2019 Category: Biotechnology Source Type: research