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

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.

Enterococcus faecalis Uses a Phosphotransferase System Permease and a Host Colonization-Related ABC Transporter for Maltodextrin Uptake

“…However, the utilization of maltotriose by the malT mutant via the ABC transporter was less efficient than that of maltotetraose, but it was similarly efficient as the utilization of the two trisaccharides panose and isopanose by the wild-type strain. In conclusion, E. faecalis transports maltotriose and maltotetraose, which are usually present in maltodextrin, by mechanisms and transporters which strongly resemble those reported for S. mutans (20) but which exhibit significant differences from those reported for other streptococci, such as S. pyogenes (19) and S. pneumoniae (2). To the best of our knowledge, the transport of the maltotriose linkage isomers panose and isopanose, which are usually also present in small amounts in maltodextrin, has not been studied in bacteria.…”

“…It therefore seems that an unknown carbohydrate transporter, possibly an ABC transporter or a PTS permease, is responsible for the residual growth on maltose observed for the malT mutant. An identical observation was made for S. pneumoniae, where, similarly to the malT single mutant, the malT mdxE double mutant was also able to grow slowly on maltose (2). However, in contrast to S. pneumoniae, which takes up maltotriose equally well by MalT and the ABC transporter, E. faecalis transports the trisaccharide primarily by the PTS and only slowly by MdxEFG-MsmX.…”

“…Maltooligosaccharides are almost exclusively taken up by the ABC transporter. The residual maltose uptake observed for the malT mutant is not catalyzed by the ABC transporter (2).…”

The ABC Transporter Encoded at the Pneumococcal Fructooligosaccharide Utilization Locus Determines the Ability To Utilize Long- and Short-Chain Fructooligosaccharides

“…Subsequently, it was demonstrated that growth of an scrT mutant on sucrose was greatly reduced. Although loss of susX, encoding the substrate binding protein of the predicted ABC transporter, did not reduce growth on sucrose, growth of a mutant deficient in both scrT and susX was further reduced (6). These data suggest that scrT encodes the major sucrose transporter.…”

Metabolic Fate of Unsaturated Glucuronic/Iduronic Acids from Glycosaminoglycans

“…Two streptococci, S. pneumoniae and S. pyogenes, have been shown to grow on hyalruonan as the sole carbon source (11)(12)(13), but little knowledge about the bacterial assimilation mechanism of glycosaminoglycans has been accumulated. More recently, streptococcal UGL has been demonstrated to act on various unsaturated disaccharides, such as hyaluronan, chondroitin sulfate, heparin, and heparan sulfate, and to release unsaturated uronic acids and amino sugars (9,14).…”