The exometabolome of Clostridium thermocellum reveals overflow metabolism at high cellulose loading

作者：Evert Klaas Holwerda, Philip G. Thorne, Daniel G. Olson, Daniel Amador‐Noguez, Nancy L. Engle, Timothy James Tschaplinski, Johannes P. van Dijken, Lee Rybeck Lynd · 发表于：Biotechnology for Biofuels · 年份：2014 · DOI：10.1186/s13068-014-0155-1 · 被引用次数：134 · 研究领域：Biofuel production and bioconversion、Advanced Cellulose Research Studies、Polysaccharides and Plant Cell Walls

BACKGROUND: Clostridium thermocellum is a model thermophilic organism for the production of biofuels from lignocellulosic substrates. The majority of publications studying the physiology of this organism use substrate concentrations of ≤10 g/L. However, industrially relevant concentrations of substrate start at 100 g/L carbohydrate, which corresponds to approximately 150 g/L solids. To gain insight into the physiology of fermentation of high substrate concentrations, we studied the growth on, and utilization of high concentrations of crystalline cellulose varying from 50 to 100 g/L by C. thermocellum. RESULTS: Using a defined medium, batch cultures of C. thermocellum achieved 93% conversion of cellulose (Avicel) initially present at 100 g/L. The maximum rate of substrate utilization increased with increasing substrate loading. During fermentation of 100 g/L cellulose, growth ceased when about half of the substrate had been solubilized. However, fermentation continued in an uncoupled mode until substrate utilization was almost complete. In addition to commonly reported fermentation products, amino acids - predominantly L-valine and L-alanine - were secreted at concentrations up to 7.5 g/L. Uncoupled metabolism was also accompanied by products not documented previously for C. thermocellum, including isobutanol, meso- and RR/SS-2,3-butanediol and trace amounts of 3-methyl-1-butanol, 2-methyl-1-butanol and 1-propanol. We hypothesize that C. thermocellum uses overflow metabolism t...