A minimal growth medium for the basidiomycete Pleurotus sapidus for metabolic flux analysis
BACKGROUND: Pleurotus sapidus secretes a huge enzymatic repertoire including hydrolytic and oxidative enzymes and is an example for higher basidiomycetes being interesting for biotechnology. The complex growth media used for submerged cultivation limit basic physiological analyses of this group of organisms. Using undefined growth media, only ... little insights into the operation of central carbon metabolism and biomass formation, i.e., the interplay of catabolic and anabolic pathways, can be gained. RESULTS: The development of a chemically defined growth medium allowed rapid growth of P. sapidus in submerged cultures. As P. sapidus grew extremely slow in salt medium, the co-utilization of amino acids using 13C-labelled glucose was investigated by gas chromatography-mass spectrometry (GC-MS) analysis. While some amino acids were synthesized up to 90% in vivo from glucose (e.g., alanine), asparagine and/or aspartate were predominantly taken up from the medium. With this information in hand, a defined yeast free salt medium containing aspartate and ammonium nitrate as a nitrogen source was developed. The observed growth rates of P. sapidus were well comparable with those previously published for complex media. Importantly, fast growth could be observed for 4days at least, up to cell wet weights (CWW) of 400gL-1. The chemically defined medium was used to carry out a 13C-based metabolic flux analysis, and the in vivo reactions rates in the central carbon metabolism of P. sapidus were investigated. The results revealed a highly respiratory metabolism with high fluxes through the pentose phosphate pathway and TCA cycle. CONCLUSIONS: The presented chemically defined growth medium enables researchers to study the metabolism of P. sapidus, significantly enlarging the analytical capabilities. Detailed studies on the production of extracellular enzymes and of secondary metabolites of P. sapidus may be designed based on the reported data.