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. 2019 Jan;7(1):10.1128/microbiolspec.psib-0011-2018.
doi: 10.1128/microbiolspec.PSIB-0011-2018.

Gram-Positive Type IV Pili and Competence

Sandra Muschiol  1   2 , Marie-Stephanie Aschtgen  1   2 , Priyanka Nannapaneni  1   2 , Birgitta Henriques-Normark  1   2
Affiliations

Gram-Positive Type IV Pili and Competence

Sandra Muschiol et al. Microbiol Spectr. 2019 Jan.

Abstract

Type IV pili (T4P) are remarkable bacterial surface appendages that carry out a range of functions. Various types of T4P have been identified in bacteria and archaea, making them almost universal structures in prokaryotes. T4P are best characterized in Gram-negative bacteria, in which pilus biogenesis and T4P-mediated functions have been studied for decades. Recent advances in microbial whole-genome sequencing have provided ample evidence for the existence of T4P also in many Gram-positive species. However, comparatively little is known, and T4P in Gram-positive bacteria are just beginning to be dissected. So far, they have mainly been studied in Clostridium and Streptococcus spp. and are involved in diverse cellular processes such as adhesion, motility, and horizontal gene transfer. Here we summarize the current understanding of T4P in Gram-positive species and their functions, with particular focus on the type IV competence pilus produced by the human pathogen Streptococcus pneumoniae and its role in natural transformation.

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Figures

FIGURE 1
FIGURE 1
Type IV competence pilus produced by S. pneumoniae R6. The pilus was visualized by transmission electron microscopy after negative staining with uranyl acetate. Scale bar, 100 nm.
FIGURE 2
FIGURE 2
Schematic representation of the DNA uptake machinery in competent S. pneumoniae. Upon competence induction, the pneumococcal competence pilus composed of ComGC is made and captures extracellular, transforming DNA (15). Captured DNA is passed to the DNA receptor ComEA and the transmembrane channel protein ComEC. This step is possibly mediated by an unknown retraction ATPase and subsequent pilus retraction or yet another undescribed mechanism. Double-stranded DNA (dsDNA) is cleaved by the endonuclease EndA and single-stranded DNA (ssDNA) enters the cytoplasm through the ComEC pore driven by the DNA-dependent ATPase ComFA (48). ComFA forms a complex with ComFC and DprA (49) and together with SsbB and RecA help in stabilization and processing of internalized ssDNA to facilitate genetic exchange (24).
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