title: Cometabolism of a nongrowth substrate: L-serine utilization by Corynebacterium glutamicum.
abstract: Despite its key position in central metabolism, L-serine does not support the growth of Corynebacterium glutamicum. Nevertheless, during growth on glucose, L-serine is consumed at rates up to 19.4 +/- 4.0 nmol min(-1) (mg [dry weight])(-1), resulting in the complete consumption of 100 mM L-serine in the presence of 100 mM glucose and an increased growth yield of about 20%. Use of 13C-labeled L-serine and analysis of cellularly derived metabolites by nuclear magnetic resonance spectroscopy revealed that the carbon skeleton of L-serine is mainly converted to pyruvate-derived metabolites such as L-alanine. The sdaA gene was identified in the genome of C. glutamicum, and overexpression of sdaA resulted in (i) functional L-serine dehydratase (L-SerDH) activity, and therefore conversion of L-serine to pyruvate, and (ii) growth of the recombinant strain on L-serine as the single substrate. In contrast, deletion of sdaA decreased the L-serine cometabolism rate with glucose by 47% but still resulted in degradation of L-serine to pyruvate. Cystathionine beta-lyase was additionally found to convert L-serine to pyruvate, and the respective metC gene was induced 2.4-fold under high internal L-serine concentrations. Upon sdaA overexpression, the growth rate on glucose is reduced 36% from that of the wild type, illustrating that even with glucose as a single substrate, intracellular L-serine conversion to pyruvate might occur, although probably the weak affinity of L-SerDH (apparent Km, 11 mM) prevents substantial L-serine degradation.
authors.affiliation: Institut für Biotechnologie, Forschungszentrum Jülich GmbH, Jülich, Germany.
authors.forename: Roman
authors.initials: R
authors.lastname: Netzer
authors.forename: Petra
authors.initials: P
authors.lastname: Peters-Wendisch
authors.forename: Lothar
authors.initials: L
authors.lastname: Eggeling
authors.forename: Hermann
authors.initials: H
authors.lastname: Sahm
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002247:Carbon Isotopes / Q000378:metabolism; D048230:Corynebacterium glutamicum / Q000254:growth & development* / Q000378:metabolism*; D003470:Culture Media; D017353:Gene Deletion; D005947:Glucose / Q000378:metabolism*; D012695:L-Serine Dehydratase / Q000235:genetics / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D020411:Oligonucleotide Array Sequence Analysis; D012694:Serine / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002247:Carbon Isotopes; D003470:Culture Media; D012694:Serine; D012695:L-Serine Dehydratase; D005947:Glucose