To investigate the underlying transfer mechanism, we performed a systematic molecular dissection of the 89K PAI. Based on our previously reported comparative sequence analysis, 89K is located in the genome of S. suis strain 05ZYH33 at a position between 05SSU0902 (hyd) and 05SSU0983 (rplL), which encode a predicted hydrolase and the 50S ribosomal protein L7/L12 respectively (Chen et al., 2007) . A total of 80 open reading frames (ORFs) were annotated in the 89K island, most of them (n = 65) on the minus strand. The overall gene organization in 89K is presented in Fig. 1 . Notably, 89K contains a Tn916 element, which is likely associated with the tetracycline resistance phenotype because the S. suis 2 reference P1/7 strain without 89K is sensitive to tetracycline. Furthermore, 89K carries a large lantibiotic biosynthesis cluster, which was suggested to be incapable of producing a functional lantibiotic (due to mutation) but essential for full virulence (Phelps and Neely, 2007; Holden et al., 2009 ).