Functional analysis of an unusual type IV pilus in the Gram‐positive Streptococcus sanguinis

• Published in: Molecular microbiology Vol. 99; no. 2; pp. 380 - 392
• Main Authors: Gurung, Ishwori, Spielman, Ingrid, Davies, Mark R., Lala, Rajan, Gaustad, Peter, Biais, Nicolas, Pelicic, Vladimir
• Format: Journal Article
• Language: English
• Published: England Wiley 01.01.2016; John Wiley and Sons Inc
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Fimbriae Proteins - genetics; Fimbriae Proteins - metabolism; Fimbriae, Bacterial - genetics; Fimbriae, Bacterial - metabolism; Life Sciences; Microbiology and Parasitology; Streptococcus - cytology; Streptococcus - genetics; Streptococcus - metabolism; Streptococcus sanguinis
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.13237

Summary Type IV pili (Tfp), which have been studied extensively in a few Gram‐negative species, are the paradigm of a group of widespread and functionally versatile nano‐machines. Here, we performed the most detailed molecular characterisation of Tfp in a Gram‐positive bacterium. We demonstrate that the naturally competent Streptococcus sanguinis produces retractable Tfp, which like their Gram‐negative counterparts can generate hundreds of piconewton of tensile force and promote intense surface‐associated motility. Tfp power ‘train‐like’ directional motion parallel to the long axis of chains of cells, leading to spreading zones around bacteria grown on plates. However, S. sanguinis Tfp are not involved in DNA uptake, which is mediated by a related but distinct nano‐machine, and are unusual because they are composed of two pilins in comparable amounts, rather than one as normally seen. Whole genome sequencing identified a locus encoding all the genes involved in Tfp biology in S. sanguinis. A systematic mutational analysis revealed that Tfp biogenesis in S. sanguinis relies on a more basic machinery (only 10 components) than in Gram‐negative species and that a small subset of four proteins dispensable for pilus biogenesis are essential for motility. Intriguingly, one of the piliated mutants that does not exhibit spreading retains microscopic motility but moves sideways, which suggests that the corresponding protein controls motion directionality. Besides establishing S. sanguinis as a useful new model for studying Tfp biology, these findings have important implications for our understanding of these widespread filamentous nano‐machines. Type IV pili (Tfp) are functionally versatile and widespread filamentous nano‐machines studied mainly in Gram‐negative species until now. We show here that S. sanguinis is a new Gram‐positive model for studying the complex biology of Tfp. We found that S. sanguinis uses a rudimentary machinery to produce Tfp unusually composed of two pilins, which can retract, generate tremendous tension forces and promote intense motility, but are not involved in DNA uptake.