A Type IV Pilus Mediates DNA Binding during NaturalTransformation in Streptococcus pneumoniae

Raphae¨Laurenceau, Ge´rard Pe´hau-Arnaudet, Sonia Baconnais, Joseph Gault,

Christian Malosse, Annick Dujeancourt, Nathalie Campo, Julia Chamot-Rooke, Eric Le Cam,

Jean-Pierre Claverys, Re´mi Fronzes. PLoS Pathog 9(6): e1003473

Speaker: Dong Sheng Lin (林東昇)                             Time: 14:00~15:00, Oct. 9, 2013

Commentator: Dr. Lien-I Hor (何漣漪 老師)             Place: Room 601

Abstract

Natural transformation is a process that increases bacterial adaptability and plasticity through genetic exchange. Streptococcus pneumonia, a major human pathogen with the ability to cause pneumonia, meningitis and septicemia, can acquire resistance to antibiotics and escape vaccines through transformation. Transformation requires the binding and internalization of external DNA, however the detail molecular mechanism is not known. All transformable Gram-positive bacteria carry a comG operon that resembles operons encoding Type IV pili and Type II secretionpseduopili in Gram-negative bacteria, as well as a gene encoding a prepilin peptidase homolog, pilD. comG and pilD genes are expressed only in competent B. subtilis and S. pneumoniae cells and are required for their transformation. In addition, a macromolecular complex containing the prepilin candiadate protein ComGC can be found at the surface of competent B. subtilis cells (1). However, no transformation appendage could be directly visualized at the surface of any competent Gram-positive bacteria. In this study, in order to see if ComGC was part of a macromolecular complex at the surface of competent S. pneumoniae cells, the authors used mechanical shearing, which has been used in the past to separate surface appendages in Pseudomonas aeruginosa, to purify potential S. pneumoniae specific appendages. The results showed that ComGC is part of an extracellular appendage and ComGA is necessary for the assembly of such appendage. Next, the authors detected the ComGC-containing appendage at the surface of competent S. pneumoniae by immuno-fluorescence and electron microscopy. These ComGC-containing appendages were further analyzed using biochemical and morphological studies and the results suggested that it is similar to a typical Gram-negative Type IV pili. Furthermore, the authors proved that these newly identified Type IV pili in S. pneumoniae are required for transformation by direct binding to DNA. In conclusion, the authors discovered a Gram-positive Type IV pilus in S. pneumoniae that is required for transformation via direct DNA binding.

References

1. Chen I, Provvedi R, Dubnau D. A macromolecular complex formed by a pilin-like protein in competent Bacillus subtilis. J. Biol. Chem. 2006; 281: 21720-21727.