| Summary: | Analysis of publicly available genomes of Streptococcus pneumoniae has led to the
identification of a new genomic element resembling gram-positive pilus islets (PIs). Here, we
demonstrate that this genomic region, herein referred to as PI-2 (containing the genes pitA,
sipA, pitB, srtG1, and srtG2) codes for a novel functional pilus in pneumococcus. Therefore,
there are two pilus islets identified so far in this pathogen (PI-1 and PI-2). Polymerization of
the PI-2 pilus requires the backbone protein PitB as well as the sortase SrtG1 and the signal
peptidase-like protein SipA. PI-2 is associated with serotypes 1, 2, 7F, 19A, and 19F,
considered to be emerging in both industrialized and developing countries. Interestingly,
strains belonging to clonal complex 271 (CC271) contain both PI-1 and PI-2, as revealed by
genome analyses. In these strains both pili are surface exposed and independently assembled.
Furthermore, in vitro experiments provide evidence that the pilus encoded by PI-2 of S.
pneumoniae is involved in adherence. Thus, pneumococci encode at least two types of pili
that may play a role in the initial host cell contact to the respiratory tract. In addition, the
pilus proteins are potential antigens for inclusion in a new generation of pneumococcal
vaccines.
Adherence by pili could represent important factor in bacterial community formation, since it
has been demonstrated that bacterial community formation plays an important role in
pneumococcal otitis media. In vitro quantification of bacterial community formation by S.
pneumoniae was performed in order to investigate the possible role of pneumococcal pili to
form communities. By using different growth media we were not able to see clear association
between pili and community formation. But our findings revealed that strains belonging to
MLST clonal complex CC15 efficiently form bacterial communities in vitro in a glucose
dependent manner.
We compared the genome of forty-four pneumococcal isolates discovering four open reading
frames specifically associated with CC15. These four genes are annotated as members of an
operon responsible for the biosynthesis of a putative lanctibiotic peptide, described to be
involved in bacterial community formation. Our experiments show that the lanctibiotic
operon deletion affects glucose mediated community formation in CC 15 strain INV200.
Moreover, since glucose consumption during bacterial growth produce an acidic
environment, we tested bacterial community formation at different pH and we showed that
the lanctibiotic operon deletion affected pH mediated community formation in CC 15 strain
INV200. In conclusion, these data demonstrate that the putative lanctibiotic operon is
associated with pneumococcal CC 15 strains in vitro bacterial community formation.
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