[The type IX secretion system and the type V pilus in the phylum Bacteroidetes]

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Bacteroidetes phylum bacteria, including Porphyromonas gingivalis, are significant human symbionts and pathogens.
• Porphyromonas gingivalis causes periodontitis, with gingipain protease and pili being key virulence factors.
• Previous understanding of bacterial secretion systems and pilus formation in Bacteroidetes was limited.

Purpose of the Study:

• To investigate the secretion mechanism of gingipain in Porphyromonas gingivalis.
• To characterize the biogenesis and function of P. gingivalis pili.
• To identify novel secretion systems and pilus formation mechanisms within the Bacteroidetes phylum.

Main Methods:

• Analysis of Porphyromonas gingivalis secretion pathways.
• Proteolytic degradation studies involving gingipain.
• Comparative genomic analysis across Bacteroidetes species.
• Microscopy and biochemical assays to study pilus formation.

Main Results:

• A novel secretion system, termed the Por secretion system (renamed type IX secretion system), was identified for gingipain secretion.
• This type IX secretion system is conserved across Bacteroidetes and associated with gliding motility.
• Pilus formation in P. gingivalis involves lipoprotein transport and arginine-gingipain-mediated processing.
• This unique pilus assembly mechanism (type V pili) is prevalent in the class Bacteroidia.

Conclusions:

• The type IX secretion system represents a significant discovery in bacterial protein transport within Bacteroidetes.
• The novel type V pili formation mechanism highlights unique adaptations in P. gingivalis and related bacteria.
• These findings advance our understanding of bacterial virulence, motility, and evolution in the Bacteroidetes phylum.