Regulation of PI-2b Pilus Expression in Hypervirulent Streptococcus agalactiae ST-17 BM110
Regulation of PI-2b Pilus Expression in Hypervirulent Streptococcus agalactiae ST-17 BM110
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DOI：
10.1371/journal.pone.0169840
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发表时间：
2017-01-20
期刊：
影响因子：
3.7
通讯作者：
Dramsi, Shaynoor
中科院分区：
文献类型：
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作者：
Perichon, Bruno;Szili, Noemi;Dramsi, Shaynoor
广泛传播的无乳链球菌（也称为B族链球菌，GBS）“高毒力”ST 17克隆与新生儿脑膜炎密切相关。PI-2b基因座主要存在于ST-17菌株中，但也存在于少数非ST-17人分离株中，如ST-7原型菌株A909。在此，我们分析了与非ST 17 A909相比，ST 17菌株BM 110中PI-2b菌毛的表达。比较基因组分析显示，在所有26个ST 17基因组中PI-2b操纵子上游区域存在43个碱基对（bp）的发夹样结构，这在携带PI-2b位点的8个非ST 17菌株中不存在。在菌株BM 110中缺失该43-bp序列导致PI-2b的转录增加3至5倍。通过RNAseq、引物延伸、qRT-PCR和以gfp为报告基因的转录融合对A909和BM 110菌株中PI-2b启动子区域进行表征。我们的研究结果表明，存在一个单一的启动子（Ppi 2b）与转录起始位点（TSS）映射的第一PI-2b基因的起始密码子上游37个碱基。位于PI-2 B上游的16个基因的大操纵子编码B族碳水化合物（也称为抗原B），其是细菌细胞壁的主要成分。我们发现位于抗原B和PI-2 B操纵子之间的发夹序列是转录终止子。在A909中，PI-2 B b表达的增加可能是由于抗原B操纵子的通读转录。此外，我们发现，一个延伸的5'启动子区是需要的最大转录的gfp作为一个报告基因在S。来自Ppi 2b启动子的无乳。在乳酸乳球菌菌株NZ 9000（一种相关的非致病性革兰氏阳性菌种）中进行的基因报告基因测定显示，需要GBS特异性调节因子来驱动PI-2b转录。PI-2b表达在BM 110 Delta covR突变体中与亲本BM 110菌株相比上调，但这种作用可能是间接的。总的来说，我们的研究结果表明，PI-2b的表达在GBS ST 17株，这可能会赋予人类宿主的选择性优势，无论是通过减少宿主的免疫反应和/或增加其传播的潜力。
The widely spread Streptococcus agalactiae (also known as Group B Streptococcus, GBS) "hypervirulent" ST17 clone is strongly associated with neonatal meningitis. The PI-2b locus is mainly found in ST17 strains but is also present in a few non ST17 human isolates such as the ST-7 prototype strain A909. Here, we analysed the expression of the PI-2b pilus in the ST17 strain BM110 as compared to the non ST17 A909. Comparative genome analyses revealed the presence of a 43-base pair (bp) hairpin-like structure in the upstream region of PI-2b operon in all 26 ST17 genomes, which was absent in the 8 non-ST17 strains carrying the PI-2b locus. Deletion of this 43-bp sequence in strain BM110 resulted in a 3-to 5-fold increased transcription of PI-2b. Characterization of PI-2b promoter region in A909 and BM110 strains was carried out by RNAseq, primer extension, qRT-PCR and transcriptional fusions with gfp as reporter gene. Our results indicate the presence of a single promoter (Ppi2b) with a transcriptional start site (TSS) mapped 37 bases upstream of the start codon of the first PI-2b gene. The large operon of 16 genes located upstream of PI-2b codes for the group B carbohydrate (also known as antigen B), a major constituent of the bacterial cell wall. We showed that the hairpin sequence located between antigen B and PI-2b operons is a transcriptional terminator. In A909, increased expression of PI-2b probably results from read-through transcription from antigen B operon. In addition, we showed that an extended 5' promoter region is required for maximal transcription of gfp as a reporter gene in S. agalactiae from Ppi2b promoter. Gene reporter assays performed in Lactococcus lactis strain NZ9000, a related non-pathogenic Gram-positive species, revealed that GBS-specific regulatory factors are required to drive PI-2b transcription. PI-2b expression is up-regulated in the BM110 Delta covR mutant as compared to the parental BM110 strain, but this effect is probably indirect. Collectively, our results indicate that PI-2b expression is regulated in GBS ST17 strains, which may confer a selective advantage in the human host either by reducing host immune responses and/or increasing their dissemination potential.