Investigation of Type Iv Pili and Twitching Motility in the Fitness and Pathogenic Capacity of Streptococcus Sanguinis

Streptococcus sanguinis, an early colonizer of the oral biofilm, is a frequent isolate of the oral microbiome and an opportunistic pathogen for systemic infections. Recent genomic studies have discovered that S. sanguinis is the only known streptococcus possessing a pil gene cluster for the biosynthesis of Type IV pili (Tfp); however, the role of Tfp in the fitness of S. sanguinis is unknown. Additionally, although the pil cluster is commonly present in the genome of S. sanguinis and all sequenced clusters harbor pilT, encoding a retraction ATPase for twitching motility, the Tfp-mediated twitching motility on agar plates was detected only in limited strains under anaerobic cultivation. This observation suggests that the expression of the pil cluster and the activation of twitching motility are regulated. Our recent transmission electron microscopy (TEM) studies on twitching-negative S. sanguinis SK36 confirmed that the expression of the pil cluster resulted in a short surface filament. Deletion of the putative pilin genes abolished the biosynthesis of this structure and significantly reduced the adherence of SK36 to host epithelial cells, indicating that Tfp of SK36 are important for host cell adherence, but not for motility. To further investigate the regulation of Tfp-mediated motility and the potential advantages of expressing twitching motility in S. sanguinis, the regulation and function of the pil cluster in two twitching-positive clinical strains, S. sanguinis CGMH010 and CGMH058, will be analyzed and compared to that of the non-twitching strain, SK36, in this proposal. We will define the mechanism that regulates the twitching activity by using various molecular analyses, TEM examination and transposon mutagenesis. Isogenic pilin-null and PilT-null derivatives will be generated to analyze the impact of Tfp and twitching motility on the biofilm formation, adherence to host cells and phagocytosis by host cells. Whether Tfp would enable S. sanguinis to better compete with other microbes in the oral biofilm will also be tested. The results of this proposal will provide insights into the impact of this unique feature in the overall capacity of S. sanguinis. Information obtained from this study may allow for the development of diagnostic and therapeutic strategies for infections caused by S. sanguinis.

Project ID:PC10901-1616
External Project ID:MOST108-2320-B182-020-MY3