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Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43
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The Streptococcus pneumoniae pilus-1 displays a biphasic expression pattern.

Gabriella De Angelis1, Monica Moschioni, Alessandro Muzzi

  • 1Novartis Vaccines and Diagnostics, Siena, Italy.

Plos One
|July 7, 2011
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Streptococcus pneumoniae pilus-1 exhibits biphasic expression, with distinct subpopulations of bacteria either expressing or not expressing the pilus. This on/off regulation is controlled transcriptionally, not by genetic mutation.

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Bacterial Pathogenesis

Background:

  • Pilus-1, encoded by pilus islet 1 (PI-1) in *Streptococcus pneumoniae*, is present in ~30% of clinical isolates and contributes to virulence and host cell attachment.
  • Pilus-1 expression is reportedly tightly regulated by various genetic factors, including the positive regulator RlrA.

Purpose of the Study:

  • To investigate the single-cell level expression patterns of pilus-1 in *Streptococcus pneumoniae*.
  • To elucidate the regulatory mechanisms underlying pilus-1 expression and its potential bistable nature.

Main Methods:

  • Single-cell analysis of pilus expression in PI-1 positive strains.
  • Colony selection and immuno-detection to enrich for pilus-expressing and non-expressing subpopulations.
  • PI-1 sequencing, microarray expression profiling, and Western blot analysis.
  • Investigating the role of the RlrA regulator in pilus expression.

Main Results:

  • Pilus-1 expression in PI-1 positive strains is biphasic, with two distinct subpopulations: one expressing pilus and one not.
  • This biphasic expression is not influenced by genotype, serotype, growth conditions, or antibodies, and is not due to PI-1 mutations.
  • Regulation occurs at the transcriptional level (on/off), without concurrent regulation of other genes.
  • Over-expression of RlrA can induce pilus expression in pilus-1 negative bacteria.

Conclusions:

  • The biphasic pilus expression in *Streptococcus pneumoniae* suggests a phenomenon of bistability.
  • Pilus expression is regulated transcriptionally, with RlrA playing a key role in its induction.