Prevalence of Type IV Pili-Mediated Twitching Motility in Streptococcus sanguinis Strains and Its Impact on Biofilm Formation and Host Adherence

Abstract

Although the gene clusters encoding Tfp are commonly present in Streptococcus sanguinis , not all strains express surface-dependent twitching motility on agar surfaces. Regardless of whether the Tfp could drive motility, Tfp can serve as a ligand for the colonization of host cells.

Functional Analysis of the Major Pilin Proteins of Type IV Pili in Streptococcus sanguinis CGMH010

“…Our recent functional studies on two S. sanguinis strains encoding three pilA paralogs, the motile CGMH010 and non-motile SK36, confirmed that Tfp are essential for optimal adherence to host cells, regardless of motility [14]. Here, we investigated the role of the three highly homologous major pilins of CGMH010 and found that each protein exhibits different effects on the structure and activity of Tfp.…”

“…Tfp are known to mediate surface-dependent twitching motility, genetic transformation, surface sensing, adherence, and biofilm formation [4,16]. The functional significance of Tfp has been extensively studied in Gram-negative pathogens, including Neisseria meningitidis [17] and P. aeruginosa [18,19], while in Gram-positive systems, where Type IVa Tfp have not been widely explored, similar functions have also been described [8,9,14,20,21]. Gramnegative bacteria employ a single system for all observed activities, whereas Gram-positive bacteria utilize two independent Tfp systems for twitching motility and natural competence.…”

“…Some minor pilin proteins constitute an initiation complex to prime Tfp biosynthesis, and others act as ligands for interaction with host cells [11][12][13]. Notably, the Gram-negative systems generally feature a single major pilin protein, whereas S. sanguinis commonly harbors two to three homologous major pilin proteins [14]. Additionally, the Tfp system contains two ATPases for extension (PilB) and retraction (PilT/U) of the Tfp, respectively.…”

“…Specifically, Streptococcus pneumoniae utilizes Tfp comprising Com proteins for DNA uptake during genetic transformation but not for surface-dependent twitching motility, despite the Tfp being morphologically identical to the motility-driven Tfp [22]. On the other hand, S. sanguinis utilizes a Com system for DNA uptake [23] and the Tfp produced by the pil operon for twitching motility and the adherence of host cells [8,9,14]. Similarly, the Tfp of Clostridium spp.…”

“…For example, among the most-studied S. sanguinis strains, strains SK36 and CGMH010 contain three major pilin genes, pilA1, pilA2, and pilA3, whereas strain 2908 contains two major pilin genes: pilE1 and pilE2. Most of the pil genes share a sequence identity of approximately 90% or higher at the deduced amino acid level among homologs across strains, though loci encoding the major and minor pilins exhibit less conservation [14]. Previously, we examined the sequences of the pilA genes of 30 clinical isolates and found that although pilA genes are relatively less conserved between strains, significant identities between PilA proteins are present within a strain.…”