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

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

12 Scopus citations


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.

Original languageEnglish
Article numbere02788-18
JournalApplied and Environmental Microbiology
Issue number6
StatePublished - 01 03 2019

Bibliographical note

Publisher Copyright:
© 2019 American Society for Microbiology.


  • Adherence
  • Biofilms
  • CcpA
  • Streptococcus sanguinis
  • Type IV pilus


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