CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
Mol Microbiol. 2011 Mar;79(6):1670-83. doi: 10.1111/j.1365-2958.2011.07553.x. Epub 2011 Feb 10.
Pathogenicity islands (PAIs), a distinct type of genomic island (GI), play important roles in the rapid adaptation and increased virulence of pathogens. 89K is a newly identified PAI in epidemic Streptococcus suis isolates that are related to the two recent large-scale outbreaks of human infection in China. However, its mechanism of evolution and contribution to the epidemic spread of S. suis 2 remain unknown. In this study, the potential for mobilization of 89K was evaluated, and its putative transfer mechanism was investigated. We report that 89K can spontaneously excise to form an extrachromosomal circular product. The precise excision is mediated by an 89K-borne integrase through site-specific recombination, with help from an excisionase. The 89K excision intermediate acts as a substrate for lateral transfer to non-89K S. suis 2 recipients, where it reintegrates site-specifically into the target site. The conjugal transfer of 89K occurred via a GI type IV secretion system (T4SS) encoded in 89K, at a frequency of 10(-6) transconjugants per donor. This is the first demonstration of horizontal transfer of a Gram-positive PAI mediated by a GI-type T4SS. We propose that these genetic events are important in the emergence, pathogenesis and persistence of epidemic S. suis 2 strains.
致病岛（PAIs）是一种独特的基因组岛（GIs），在病原体的快速适应和毒力增加中发挥重要作用。89K 是在与中国最近两次大规模人感染相关的流行猪链球菌分离株中新发现的 PAI。然而，其进化机制及其对猪链球菌 2 流行传播的贡献尚不清楚。在本研究中，评估了 89K 的易位潜力，并研究了其可能的转移机制。我们报告 89K 可以自发切除形成染色体外的环形产物。精确切除是由 89K 携带的整合酶通过位点特异性重组介导的，需要内切酶的帮助。89K 切除中间体可作为侧向转移到非 89K 猪链球菌 2 受体的底物，在受体中它特异性地重新整合到靶位点。89K 通过 89K 编码的 GI 型 IV 型分泌系统（T4SS）进行共轭转移，供体的转移频率为 10(-6)转导子。这是首次证明革兰氏阳性 PAI 通过 GI 型 T4SS 进行水平转移。我们提出，这些遗传事件对于流行的猪链球菌 2 菌株的出现、发病机制和持续存在非常重要。
