Molecular and Functional Analysis of the Type IV Pilus Gene Cluster in Streptococcus sanguinis SK36

Yi-Ywan M Chen; Yi-Chien Chiang; Tzu-Ying Tseng; Hui-Yu Wu; Yueh-Ying Chen; Chia-Hua Wu; Cheng-Hsun Chiu

doi:10.1128/AEM.02788-18

Molecular and Functional Analysis of the Type IV Pilus Gene Cluster in Streptococcus sanguinis SK36

Appl Environ Microbiol. 2019 Mar 6;85(6):e02788-18. doi: 10.1128/AEM.02788-18. Print 2019 Mar 15.

Authors

Yi-Ywan M Chen^{1

2

3

4}, Yi-Chien Chiang², Tzu-Ying Tseng², Hui-Yu Wu², Yueh-Ying Chen⁵, Chia-Hua Wu⁵, Cheng-Hsun Chiu⁴

Affiliations

¹ Department of Microbiology and Immunology, College of Medicine, Chang Gung University, Taoyuan, Taiwan mchen@mail.cgu.edu.
² Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
³ Research Center for Pathogenic Bacteria, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
⁴ Molecular Infectious Disease Research Center, Chang Gung Memorial Hospital, Linkou, Taiwan.
⁵ Department of Microbiology and Immunology, College of Medicine, Chang Gung University, Taoyuan, Taiwan.

Abstract

Streptococcus sanguinis, dominant in the oral microbiome, is the only known streptococcal species possessing a pil gene cluster for the biosynthesis of type IV pili (Tfp). Although this cluster is commonly present in the genome of S. sanguinis, 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 S. sanguinis 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-cat 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 pil genes downregulated biofilm formation by S. sanguinis 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 pil cluster is subject to complex regulation.IMPORTANCE 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 Streptococcus sanguinis 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 S. sanguinis could more effectively utilize this structure to adhere to host cells and to interact with other microbes within the same niche.

Keywords: CcpA; Streptococcus sanguinis; adherence; biofilms; type IV pilus.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Bacterial Adhesion
Fimbriae Proteins / genetics
Fimbriae Proteins / metabolism*
Fimbriae, Bacterial / genetics
Fimbriae, Bacterial / metabolism*
Gene Expression Regulation, Bacterial
HeLa Cells
Humans
Multigene Family*
Promoter Regions, Genetic
Streptococcal Infections / microbiology
Streptococcus sanguis / genetics*

Substances

Fimbriae Proteins