Mutations in the Gene Encoding the Ancillary Pilin Subunit of the Streptococcus suis srtF Cluster Result in Pili Formed by the Major Subunit Only

Abstract

Pili have been shown to contribute to the virulence of different Gram-positive pathogenic species. Among other critical steps of bacterial pathogenesis, these structures participate in adherence to host cells, colonization and systemic virulence. Recently, the presence of at least four discrete gene clusters encoding putative pili has been revealed in the major swine pathogen and emerging zoonotic agent Streptococcus suis. However, pili production by this species has not yet been demonstrated. In this study, we investigated the functionality of one of these pili clusters, known as the srtF pilus cluster, by the construction of mutant strains for each of the four genes of the cluster as well as by the generation of antibodies against the putative pilin subunits. Results revealed that the S. suis serotype 2 strain P1/7, as well as several other highly virulent invasive S. suis serotype 2 isolates express pili from this cluster. However, in most cases tested, and as a result of nonsense mutations at the 5′ end of the gene encoding the minor pilin subunit (a putative adhesin), pili were formed by the major pilin subunit only. We then evaluated the role these pili play in S. suis virulence. Abolishment of the expression of srtF cluster-encoded pili did not result in impaired interactions of S. suis with porcine brain microvascular endothelial cells. Furthermore, non-piliated mutants were as virulent as the wild type strain when evaluated in a murine model of S. suis sepsis. Our results show that srtF cluster-encoded, S. suis pili are atypical compared to other Gram-positive pili. In addition, since the highly virulent strains under investigation are unlikely to produce other pili, our results suggest that pili might be dispensable for critical steps of the S. suis pathogenesis of infection.

Pilus Biogenesis in Lactococcus lactis: Molecular Characterization and Role in Aggregation and Biofilm Formation

“…Pili are long filaments displayed on bacterial surface and due to their adhesive properties are involved in the first stages of host colonization [47]. In Gram-positive pathogens, study of the mechanism of pilus assembly and the functions of pili in the genera Actinomyces, Bacillus, Corynebacterium , Enterococcus and Streptococcus has been considerable in recent years [22], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [80]. The ultimate objectives of these studies are to find new drug targets and to characterize pili components as new vaccine candidates [52], [81].…”

“…Their formation was discovered by pioneering works in Actinomyces naeslundii [35], [36] and Corynebacterium diphtheriae [37], and later in Bacillus cereus [38], Bacillus anthracis [39], Enterococcus faecalis [40], Enterococcus faecium [41], and species of the genus Streptococcus including S. agalactiae [22], [42], S. pneumoniae [43], S. pyogenes [44], [45], and S. suis [46]. Pili are proteinaceous appendages of 1–10 nm in diameter protruding 2–3 µm outside of bacterial cells.…”

Contribution of the Rgg Transcription Regulator to Metabolism and Virulence of Streptococcus suis Serotype 2

“…In addition, transcripts associated with protein processing and transport systems were more abundant in the ⌬rgg mutant. For example, the expression of groES/groEL, a classical molecular chaperone that plays an important role in the proper folding and assembly of macromolecular proteins, was increased, as was transcription of the srtF gene (05SSU0475), a member of the sortase family previously identified in a pilus gene cluster (10,47). Upregulation of these transcripts and many genes encoding membrane surface proteins (i.e., the Sao protein) and cell wall components could potentially enhance adhesion of the ⌬rgg mutant to Hep-2 cells.…”

Genomic organization, structure, regulation and pathogenic role of pilus constituents in major pathogenic Streptococci and Enterococci

“…More recently, 4 gene clusters encoding putative pilus-like structures were identified in S. suis, designated srtBCD and srtF, srtE and srtG, according to the type of class C sortases present in the respective locus (Fittipaldi et al, 2007;Rodriguez-Ortega et al, 2008;Takamatsu et al, 2009). The most prevalent cluster, srtF, was recently studied in detail by Fittipaldi et al (2010) and Garibaldi et al (2010). For many other species, evidence for pilus gene clusters is exclusively based on bioinformatic evidence (Plyusnin et al, 2009).…”