The complete sequence, annotation and comparative analysis of the Escherichia coli IncFII family plasmid pMccB17, encoding biosynthetic and immunity functions for the antimicrobial peptide microcin B17

Microcin B17 (Mcb17) is a ribosomally synthesized and post-translationally modified peptide (RiPP), produced by Escherichia coli, that inhibits bacterial DNA gyrase in a similar way to quinolones. The Mcb17 operon, consisting of seven genes encoding biosynthetic and immunity/export functions, was originally found on a plasmid, pMccB17. This circular plasmid, previously known as pRYC17, was originally found in Escherichia coli strain LP17, isolated from the intestinal tract of a healthy newborn at Hospital La Paz, Spain and was transferred by conjugation to E. coli K-12 [Baquero et al. (1978) J. Bacteriol. 135: 342]. pMccB17 is a low copy number IncFII plasmid in the same incompatibility group as R100 and R1. Not much is known about this plasmid aside from the facts that it carries the Mcb17 operon, does not possess any conventional antibiotic resistance markers and its size was estimated to be approximately 70 kb.

We extracted the plasmid from E. coli K-12 strain RYC1000 [pMccB17] and sequenced it twice using an Illumina short-read method, firstly together with the host bacterial chromosome, then plasmid DNA was purified and sequenced separately. PCR primers were designed to close the single remaining gap via Sanger sequencing. The resulting complete sequence has 83 predicted genes, initially identified by Prokka and subsequently manually reannotated using BLAST. Comparison to other IncFII plasmids shows a large proportion of shared genes, especially in the conjugative plasmid backbone. However, pMccB17 which is a MOBF12 plasmid lacks transposable elements and in addition to the Mcb17 operon, this plasmid carries 25 genes of unknown function.