Prof. Peter J.Christie
Thursday, Oct 09, 2014 – 3:15 pm
Venue: University of Graz
Institute of Molecular Biosciences
Humboldtstrasse 46, ground floor
Lecture Hall HS 46.01
Abstract:
Enterococcus faecalis plasmid pCF10 transfers at high frequencies upon pheromone induction of the prgQ transfer operon. This operon codes for three cell-wall-anchored proteins - PrgA, PrgB (aggregation substance), and PrgC - and a type IV secretion system through which the plasmid is delivered to recipient cells. This talk will summarize our recent progress toward defining the contributions of the Prg surface proteins to plasmid transfer, biofilm formation, and virulence using the Caenorhabditis elegans infection model. We report that a combination of PrgB and extracellular DNA (eDNA), but not PrgA or PrgC, was required for extensive cellular aggregation and pCF10 transfer at wild-type frequencies. In addition to PrgB and eDNA, production of PrgA was necessary for extensive binding of enterococci to abiotic surfaces and development of robust biofilms. PrgB is a known virulence factor in mammalian infection models, and we further determined that PrgA and PrgC were required for efficient killing in the worm infection model. In addition to evidence that PrgA and PrgB functionally interact, PrgA and PrgB were shown to associate with a fibrous mesh that surrounds the E. faecalis cell surface. In silico structural analyses further showed that PrgA’s secondary structure is almost entirely á-helical, consistent with a predicted topology in which PrgA extends from the cell surface. Also intriguingly, PrgB is a structural homolog of the surface adhesion SpaB, which is of considerable interest in view of recent findings that SpaB forms amyloid fibers at the Streptococcus mutans cell surface. We propose that the pCF10-encoded Prg proteins assemble together to form an amyloid-like fibrous mesh that coats the E. faecalis cell surface and interacts with extracellular matrix components to promote robust biofilm development. In natural settings, these biofilm communities are polymicrobial in composition and thus constitute optimal environments for signal exchange, mating pair formation, and lateral gene transfer. Hence, the pheromone-responsive, conjugative plasmids of E. faecalis have retained Prg-like surface functions over evolutionary time not specifically for the act of conjugative transfer, but rather for recruitment of potential mates within complex biofilm communities