Department of Microbiology and Immunology, College of Medicine, Chang Gung University, Taoyuan, Taiwan
Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
Appl Environ Microbiol. 2019 Mar 6;85(6). doi: 10.1128/AEM.02788-18. Print 2019 Mar 15.
, dominant in the oral microbiome, is the only known streptococcal species possessing a gene cluster for the biosynthesis of type IV pili (Tfp). Although this cluster is commonly present in the genome of , most of the strains do not express Tfp-mediated twitching motility. Thus, this study was designed to investigate the biological functions encoded by the cluster in the twitching-negative strain SK36. We found that the cluster was transcribed as an operon, with three promoters located 5' to the cluster and one in the intergenic region between SSA_2307 and SSA_2305. Studies using promoter- fusion strains revealed that the transcription of the cluster was mainly driven by the distal 5' promoter, which is located more than 800 bases 5' to the first gene of the cluster, SSA_2318. Optimal expression of the cluster occurred at the early stationary growth phase in a CcpA-dependent manner, although a CcpA-binding consensus is absent in the promoter region. Expression of the cluster resulted in a short hairlike surface structure under transmission electron microscopy. Deletion of the putative pilin genes (SSA_2313 to SSA_2315) abolished the biosynthesis of this structure and significantly reduced the adherence of SK36 to HeLa and SCC-4 cells. Mutations in the genes downregulated biofilm formation by SK36. Taken together, the results demonstrate that Tfp of SK36 are important for host cell adherence, but not for motility, and that expression of the cluster is subject to complex regulation. The proteins and assembly machinery of the type IV pili (Tfp) are conserved throughout bacteria and archaea, and yet the function of this surface structure differs from species to species and even from strain to strain. As seen in SK36, the expression of the Tfp gene cluster results in a hairlike surface structure that is much shorter than the typical Tfp. This pilus is essential for the adherence of SK36 but is not involved in motility. Being a member of the highly diverse dental biofilm, perhaps could more effectively utilize this structure to adhere to host cells and to interact with other microbes within the same niche.
在口腔微生物组中占主导地位的 是唯一已知的具有用于合成 IV 型菌毛 (Tfp) 的基因簇的链球菌种。尽管该簇通常存在于 的基因组中，但大多数菌株不表达 Tfp 介导的蠕动运动。因此，本研究旨在研究在蠕动阴性菌株 SK36 中该簇编码的生物学功能。我们发现该簇作为一个操纵子转录，其三个启动子位于簇的 5'端，一个位于 SSA_2307 和 SSA_2305 之间的基因间区。使用启动子融合菌株的研究表明，该簇的转录主要由位于簇第一个基因 5'端超过 800 个碱基的远端 5'启动子驱动。尽管在启动子区域不存在 CcpA 结合的共有序列，但该簇的最佳表达发生在早期静止生长阶段，以 CcpA 依赖性方式。尽管在启动子区域不存在 CcpA 结合的共有序列，但该簇的最佳表达发生在早期静止生长阶段，以 CcpA 依赖性方式。表达该簇导致在透射电子显微镜下观察到短的发状表面结构。缺失推定的菌毛基因 (SSA_2313 至 SSA_2315) 会破坏该结构的生物合成，并显著降低 SK36 对 HeLa 和 SCC-4 细胞的粘附。基因的突变使 SK36 的生物膜形成减少。总之，结果表明 SK36 的 Tfp 对于宿主细胞粘附很重要，但对于运动不重要，并且 簇的表达受到复杂的调节。IV 型菌毛 (Tfp) 的蛋白质和组装机制在细菌和古细菌中是保守的，但这种表面结构的功能在不同物种甚至不同菌株中都有所不同。如在 SK36 中所见，Tfp 基因簇的表达导致发状表面结构比典型的 Tfp 短得多。这种菌毛对于 SK36 的粘附是必需的，但不参与运动。作为高度多样化的牙菌斑的成员，可能更有效地利用这种结构来粘附宿主细胞，并与同一生态位内的其他微生物相互作用。
