A Functional Genomics Approach to Establish the Complement of Carbohydrate Transporters in Streptococcus pneumoniae

Alessandro Bidossi,Francesca Decorosi,Marco Rinaldo Oggioni,Susanna Ricci,Josef Deutscher,Gianni Pozzi,Leonarda Colomba,Laura Mulas,Carlo Viti,Eliane Namie Miyaji

doi:10.1371/journal.pone.0033320

Abstract

The aerotolerant anaerobe Streptococcus pneumoniae is part of the normal nasopharyngeal microbiota of humans and one of the most important invasive pathogens. A genomic survey allowed establishing the occurrence of twenty-one phosphotransferase systems, seven carbohydrate uptake ABC transporters, one sodium∶solute symporter and a permease, underlining an exceptionally high capacity for uptake of carbohydrate substrates. Despite high genomic variability, combined phenotypic and genomic analysis of twenty sequenced strains did assign the substrate specificity only to two uptake systems. Systematic analysis of mutants for most carbohydrate transporters enabled us to assign a phenotype and substrate specificity to twenty-three transport systems. For five putative transporters for galactose, pentoses, ribonucleosides and sulphated glycans activity was inferred, but not experimentally confirmed and only one transport system remains with an unknown substrate and lack of any functional annotation. Using a metabolic approach, 80% of the thirty-two fermentable carbon substrates were assigned to the corresponding transporter. The complexity and robustness of sugar uptake is underlined by the finding that many transporters have multiple substrates, and many sugars are transported by more than one system. The present work permits to draw a functional map of the complete arsenal of carbohydrate utilisation proteins of pneumococci, allows re-annotation of genomic data and might serve as a reference for related species. These data provide tools for specific investigation of the roles of the different carbon substrates on pneumococcal physiology in the host during carriage and invasive infection.

Highlights

Streptococcus pneumoniae, the main cause of community acquired pneumonia, is one of the most important human pathogens and a frequent etiologic agent of sepsis, meningitis, otitis media and conjunctivitis [1]
Carbohydrate uptake systems account for a large fraction of the pneumococcal chromosome and include a series of phosphotransferase system (PTS) systems, and carbohydrate specific ATP-binding cassette (ABC) transporters, glycerol permeases and one sodium:solute symporter
The relative genomic and functional characterisation of each transport system is reported in separate sections of the manuscript

Summary

Introduction

Streptococcus pneumoniae, the main cause of community acquired pneumonia, is one of the most important human pathogens and a frequent etiologic agent of sepsis, meningitis, otitis media and conjunctivitis [1]. The colonisation of the human nasopharyngeal mucosa by S. pneumoniae is a natural process that occurs during the first few months of life. Most colonised individuals are asymptomatic, but occasionally progression towards disease occurs, generally early after acquisition of a new strain [4,6,7]. Both carriage and pneumococcal invasive disease show a clear seasonal variation with a peak in winter, which coincides with the seasonal peak of viral respiratory infections and indicates multivariant environmental influences on host-microbe interaction and pathogenesis of disease [5,8]. We have shown that the nine carbon amino sugar sialic acid in saliva is a signal for pneumococcal virulence in the host providing a possible molecular explanation of the epidemiologic correlation between influenza and pneumococcal pneumonia [9]

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