[ODP-083] Discovery of integrative elements with strand-biased circularization activity
The exchange of antimicrobial resistance (AMR) genes between aquaculture and terrestrial microbial populations has emerged as a public health concern. To gain insight into the genetic mechanisms underlying AMR gene transfer from marine bacteria, we mated a multidrug-resistant Vibrio alfacsensis strain with an E. coli strain, and then determined the complete genome sequences of the donor and transconjugant strains. Sequence analysis revealed a multidrug resistance conjugative plasmid in the donor strain, which was integrated into the chromosome of the recipient. The plasmid backbone in the transconjugant chromosome was flanked by two copies of a 7.1 kb unclassifiable integrative element harboring a β-lactamase gene. The 7.1 kb element and previously reported Tn6283 share four coding sequences, two of which encode tyrosine recombinases. PCR and sequencing experiments revealed that the 7.1 kb element generates a circular copy of its one specific strand without generating an empty donor site, in contrast to the movement of integron gene cassette or ICEs discovered to date; Tn6283-related elements are collectively termed SEs (strand-biased circularizing integrative elements). Overall, these results suggest that in addition to conjugative plasmids, SEs are involved in the spread of AMR genes among marine bacteria.