[ODP-041] 高頻度接合伝達・移動系CA-MRSAプラスミドがもつtra/mobオペロンの構造解析
※発表者が体調不良のため、代読による発表
Community-associated methicillin-resistant Staphylococcus aureus ST8/SCCmecIVl (CA-MRSA/J) has spread widely in Japan. Here, we show the high frequency of conjugative transfer/mobilization for CA-MRSA/J plasmids. CA-MRSA/J strain T6 has a 32-kb non-transmissible qacB, edin plasmid (pW6B). We found that strain T6 also carries a conjugative transfer plasmid (pW6A) of similar size; pW6A being 35,688-bp with 45 coding sequences (CDS), but with no drug-resistance genes. The transfer genes (tra1 to tra24) constituted a large 23-kb tra operon, with three overlapping. Of the tra genes, six (6/24, 25%) were non-ATG (GTG or TTG)-starting CDS. CTA-starting CDS was also predicted. The tra operon was flanked by two GTG-starting complement CDS. The transfer machinery was a VirB4/D4 type of the type IV secretion system, and the tra operon retained the relaxase gene (mob) and unique origin-of-transfer (oriT). pW6B also had a similar oriT, and both pW6A and pW6B existed as multicopy in a cell. pW6B mobilization occurred at a frequency of 10-3 to 10-4 (transconjugants/donor), together with pW6A in most cases (>90%). These events were filter-mating dependent. The two tightly-working-together plasmids represent an extremely high transfer in community settings, thus providing a new model of DNA transfer through the type IV secretion system, and advancing understanding of horizontal gene transfer.