Hendrickson Christina, Euler Chad W, Nguyen Scott V, Rahman Maliha, McCullor Kimberly A, King Catherine J, Fischetti Vincent A, McShan W Michael
Department of Pharmaceutical Sciences, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America.
The Biology Department, The University of Central Oklahoma, Edmond, Oklahoma, United States of America.
PLoS One. 2015 Dec 23;10(12):e0145884. doi: 10.1371/journal.pone.0145884. eCollection 2015.
Streptococcus pyogenes chromosomal island M1 (SpyCIM1) integrates by site-specific recombination into the 5' end of DNA mismatch repair (MMR) gene mutL in strain SF370SmR, blocking transcription of it and the downstream operon genes. During exponential growth, SpyCIM1 excises from the chromosome and replicates as an episome, restoring mutL transcription. This process is reversed in stationary phase with SpyCIM1 re-integrating into mutL, returning the cells to a mutator phenotype. Here we show that elimination of SpyCIM1 relieves this mutator phenotype. The downstream MMR operon genes, multidrug efflux pump lmrP, Holliday junction resolution helicase ruvA, and DNA base excision repair glycosylase tag, are also restored to constitutive expression by elimination of SpyCIM1. The presence of SpyCIM1 alters global transcription patterns in SF370SmR. RNA sequencing (RNA-Seq) demonstrated that loss of SpyCIM1 in the SpyCIM1 deletion mutant, CEM1Δ4, impacted the expression of over 100 genes involved in virulence and metabolism both in early exponential phase, when the SpyCIM1 is episomal, as well as at the onset of stationary phase, when SpyCIM1 has reintegrated into mutL. Among these changes, the up-regulation of the genes for the antiphagocytic M protein (emm1), streptolysin O (slo), capsule operon (hasABC), and streptococcal pyrogenic exotoxin (speB), are particularly notable. The expression pattern of the MMR operon confirmed our earlier observations that these genes are transcribed in early exponential phase but silenced as stationary phase is approached. Thus, the direct role of SpyCIM1 in causing the mutator phenotype is confirmed, and further, its influence upon the biology of S. pyogenes was found to impact multiple genes in addition to the MMR operon, which is a novel function for a mobile genetic element. We suggest that such chromosomal islands are a remarkable evolutionary adaptation to promote the survival of its S. pyogenes host cell in changing environments.
化脓性链球菌染色体岛M1（SpyCIM1）通过位点特异性重组整合到SF370SmR菌株中DNA错配修复（MMR）基因mutL的5'端，阻断其转录以及下游操纵子基因的转录。在指数生长期，SpyCIM1从染色体上切除并作为附加体复制，恢复mutL转录。在稳定期，此过程逆转，SpyCIM1重新整合到mutL中，使细胞恢复到突变体表型。在此我们表明，消除SpyCIM1可缓解这种突变体表型。通过消除SpyCIM1，下游MMR操纵子基因、多药外排泵lmrP、霍利迪连接点解离解旋酶ruvA和DNA碱基切除修复糖基化酶tag也恢复为组成型表达。SpyCIM1的存在改变了SF370SmR中的全局转录模式。RNA测序（RNA-Seq）表明，在SpyCIM1缺失突变体CEM1Δ4中，SpyCIM1的缺失在早期指数生长期（此时SpyCIM1为附加体）以及稳定期开始时（此时SpyCIM1已重新整合到mutL中）影响了100多个参与毒力和代谢的基因的表达。在这些变化中，抗吞噬M蛋白（emm1）、链球菌溶血素O（slo）、荚膜操纵子（hasABC）和化脓性链球菌致热外毒素（speB）的基因上调尤为显著。MMR操纵子的表达模式证实了我们之前的观察结果，即这些基因在早期指数生长期转录，但在接近稳定期时沉默。因此，SpyCIM1导致突变体表型的直接作用得到证实，此外，还发现它对化脓性链球菌生物学的影响除了MMR操纵子外还涉及多个基因，这是一种移动遗传元件的新功能。我们认为，这种染色体岛是一种显著进化适应，以促进其化脓性链球菌宿主细胞在不断变化的环境中生存。
