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Open Access Highly Accessed Research article

Regulation of neuraminidase expression in Streptococcus pneumoniae

Luciana Gualdi1, Jasvinder Kaur Hayre1, Alice Gerlini1, Alessandro Bidossi1, Leonarda Colomba1, Claudia Trappetti15, Gianni Pozzi1, Jean-Denis Docquier1, Peter Andrew2, Susanna Ricci1 and Marco R Oggioni1345*

Author Affiliations

1 Dipartimento di Biotecnologie, Università di Siena, Siena, Italy

2 Department of Infection Immunity and Inflammation, University of Leicester, Leicester, United Kingdom

3 UOC Batteriologia, Azienda Universitaria Ospedaliera Senese, Siena, Italy

4 LAMMB, Policlinico Le Scotte lotto 5 piano 1, Siena, 53100, Italy

5 Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, South Australia, 5005, Australia

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BMC Microbiology 2012, 12:200  doi:10.1186/1471-2180-12-200

Published: 11 September 2012

Abstract

Background

Sialic acid (N-acetylneuraminic acid; NeuNAc) is one of the most important carbohydrates for Streptococcus pneumoniae due of its role as a carbon and energy source, receptor for adhesion and invasion and molecular signal for promotion of biofilm formation, nasopharyngeal carriage and invasion of the lung.

Results

In this work, NeuNAc and its metabolic derivative N-acetyl mannosamine (ManNAc) were used to analyze regulatory mechanisms of the neuraminidase locus expression. Genomic and metabolic comparison to Streptococcus mitis, Streptococcus oralis, Streptococcus gordonii and Streptococcus sanguinis elucidates the metabolic association of the two amino sugars to different parts of the locus coding for the two main pneumococcal neuraminidases and confirms the substrate specificity of the respective ABC transporters. Quantitative gene expression analysis shows repression of the locus by glucose and induction of all predicted transcriptional units by ManNAc and NeuNAc, each inducing with higher efficiency the operon encoding for the transporter with higher specificity for the respective amino sugar. Cytofluorimetric analysis demonstrated enhanced surface exposure of NanA on pneumococci grown in NeuNAc and ManNAc and an activity assay allowed to quantify approximately twelve times as much neuraminidase activity on induced cells as opposed to glucose grown cells.

Conclusions

The present data increase the understanding of metabolic regulation of the nanAB locus and indicate that experiments aimed at the elucidation of the relevance of neuraminidases in pneumococcal virulence should possibly not be carried out on bacteria grown in glucose containing media.

Keywords:
Sialic acid; Metabolic regulation; Carbon catabolite repression