title: Characterization of central carbon metabolism of Streptococcus pneumoniae by isotopologue profiling.
abstract: The metabolism of Streptococcus pneumoniae was studied by isotopologue profiling after bacterial cultivation in chemically defined medium supplemented with [U-(13)C(6)]- or [1,2-(13)C(2)]glucose. GC/MS analysis of protein-derived amino acids showed lack of (13)C label in amino acids that were also essential for pneumococcal growth. Ala, Ser, Asp, and Thr displayed high (13)C enrichments, whereas Phe, Tyr, and Gly were only slightly labeled. The analysis of the labeling patterns showed formation of triose phosphate and pyruvate via the Embden-Meyerhof-Parnas pathway. The labeling patterns of Asp and Thr suggested formation of oxaloacetate exclusively via the phosphoenolpyruvate carboxylase reaction. Apparently, α-ketoglutarate was generated from unlabeled glutamate via the aspartate transaminase reaction. A fraction of Phe and Tyr obtained label via the chorismate route from erythrose 4-phosphate, generated via the pentose phosphate pathway, and phosphoenolpyruvate. Strikingly, the data revealed no significant flux from phosphoglycerate to Ser and Gly but showed formation of Ser via the reverse reaction, namely by hydroxymethylation of Gly. The essential Gly was acquired from the medium, and the biosynthesis pathway was confirmed in experiments using [U-(13)C(2)]glycine as a tracer. The hydroxymethyl group in Ser originated from formate, which was generated by the pyruvate formate-lyase. Highly similar isotopologue profiles were observed in corresponding experiments with pneumococcal mutants deficient in PavA, CodY, and glucose-6-phosphate dehydrogenase pointing to the robustness of the core metabolic network used by these facultative pathogenic bacteria. In conclusion, this study demonstrates the dual utilization of carbohydrates and amino acids under in vitro conditions and identifies the unconventional de novo biosynthesis of serine by pneumococci.
authors.affiliation: Department of Genetics of Microorganisms, Interfaculty Institute for Genetics and Functional Genomics, Ernst Moritz Arndt Universität Greifswald, Friedrich-Ludwig-Jahn-Strasse 15a, D-17487 Greifswald, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Härtel
authors.forename: Eva
authors.initials: E
authors.lastname: Eylert
authors.forename: Christian
authors.initials: C
authors.lastname: Schulz
authors.forename: Lothar
authors.initials: L
authors.lastname: Petruschka
authors.forename: Philipp
authors.initials: P
authors.lastname: Gierok
authors.forename: Stephanie
authors.initials: S
authors.lastname: Grubmüller
authors.forename: Michael
authors.initials: M
authors.lastname: Lalk
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eisenreich
authors.forename: Sven
authors.initials: S
authors.lastname: Hammerschmidt
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes / Q000494:pharmacology; D006019:Glycolysis / Q000502:physiology*; D009154:Mutation; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D002247:Carbon Isotopes; C500900:PavA protein, Streptococcus pneumoniae; D002244:Carbon