ISP, Bactéries et Risque Materno-Foetal, Université de Tours, INRA, 37032 Tours, France; Azm Center for Research in Biotechnology and its Applications, LBA3B, EDST, Lebanese University, Tripoli 1300, Lebanon.
Azm Center for Research in Biotechnology and its Applications, LBA3B, EDST, Lebanese University, Tripoli 1300, Lebanon.
Gene. 2019 Dec 15;720:144094. doi: 10.1016/j.gene.2019.144094. Epub 2019 Aug 30.
Fourteen different insertion sequences belonging to seven families were identified in the genome of Streptococcus agalactiae. Among them, IS1548, a mobile element of the ISAs1 family, was linked to clonal complex (CC) 19 strains associated with neonatal meningitis and endocarditis. IS1548 impacts S. agalactiae in two reported ways: i) inactivation of virulence genes by insertion in an open reading frame (e.g. hylB or cpsD), ii) positive modulation of the expression of a downstream gene by insertion in an intergenic region (e.g. lmb). We previously identified an unknown integration site of IS1548 in the intergenic region between the folK and the murB genes involved in folate and peptidoglycan biosynthesis, respectively. In this work, we analyzed the prevalence of IS1548 in a large collection of nine hundred and eleven S. agalactiae strains. IS1548 positive strains belong to twenty-nine different sequence types and to ten CCs. The majority of them were, however, clustered within sequence type 19 and sequence type 22, belonging to CC19 and CC22, respectively. In contrast, IS1548 targets the folK-murB intergenic region exclusively in CC19 strains. We evaluated the impact of the insertion of IS1548 on the expression of murB by locating transcriptional promoters influencing its expression in the presence or absence of IS1548 and by comparative β-galactosidase transcriptional fusion assays. We found that in the absence of IS1548, genes involved in folate biosynthesis are co-transcribed with murB. As it was postulated that a folic acid mediated reaction may be involved in cell wall synthesis, this co-transcription could be necessary to synchronize these two processes. The insertion of IS1548 in the folK-murB intergenic region disrupt this co-transcription. Interestingly, we located a promoter at the right end of IS1548 that is able to initiate additional transcripts of murB. The insertion of IS1548 in this region has thus a dual and divergent impact on the expression of murB. By comparative β-galactosidase transcriptional fusion assays, we showed that, consequently, the overall impact of the insertion of IS1548 results in a minor decrease of murB gene transcription. This study provides new insights into gene expression effects mediated by IS1548 in S. agalactiae.
在无乳链球菌基因组中鉴定出 14 个属于 7 个家族的插入序列。其中，IS1548 是 ISAs1 家族的一个移动元件，与与新生儿脑膜炎和心内膜炎相关的克隆复合体 (CC)19 菌株有关。IS1548 以两种报道的方式影响无乳链球菌：i）通过插入开放阅读框（例如 hylB 或 cpsD）使毒力基因失活，ii）通过插入基因间区（例如 lmb）正向调节下游基因的表达。我们之前在参与叶酸和肽聚糖生物合成的 folK 和 murB 基因之间的基因间区中鉴定出 IS1548 的一个未知整合位点。在这项工作中，我们分析了 911 株无乳链球菌菌株中 IS1548 的流行情况。IS1548 阳性菌株属于 29 种不同的序列类型和 10 个 CC。然而，它们中的大多数聚集在序列类型 19 和序列类型 22 中，分别属于 CC19 和 CC22。相比之下，IS1548 仅在 CC19 菌株中靶向 folK-murB 基因间区。我们通过定位影响其表达的转录启动子来评估 IS1548 插入对 murB 表达的影响，在存在或不存在 IS1548 的情况下，通过比较β-半乳糖苷酶转录融合测定进行评估。我们发现，在不存在 IS1548 的情况下，参与叶酸生物合成的基因与 murB 共转录。由于推测叶酸介导的反应可能参与细胞壁合成，这种共转录对于同步这两个过程可能是必要的。IS1548 在 folK-murB 基因间区的插入破坏了这种共转录。有趣的是，我们在 IS1548 的右端定位到一个启动子，该启动子能够启动 murB 的额外转录物。因此，IS1548 插入该区域对 murB 表达有双重和发散的影响。通过比较β-半乳糖苷酶转录融合测定，我们表明，IS1548 的插入导致 murB 基因转录的总体影响较小。这项研究提供了无乳链球菌中 IS1548 介导的基因表达效应的新见解。
