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Researchers investigated the ability of Clostridium thermocellum, a bacterium used for biofuel production, to transport and metabolize 190 different carbon substrates beyond its primary food source of cellulose. They identified 8 substrates that were fully or partially consumed, 2 that were interconverted, and 7 that may undergo conversion to unknown products, while 5 were not consumed at all. Further analysis of sorbitol and pyruvate fermentation revealed that ethanol production in this bacterium may be limited by the availability of reducing equivalents, suggesting that manipulating substrate choice can alter redox balance and product distributions.
Why it matters
This work provides a systematic characterization of C. thermocellum's metabolic capabilities and demonstrates how alternative substrates can be used as tools to manipulate fermentation outcomes. Understanding these metabolic pathways could enable optimization of biofuel and biochemical production from cellulosic biomass, potentially improving the efficiency and economics of renewable fuel generation.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
As a cellulolytic specialist microbe, Clostridium thermocellum primarily ferments cellulose and its breakdown products. However, the full breadth of its substrate range remains poorly understood. In this work, we investigated the ability of C. thermocellum to transport and metabolize a diverse range of alternative carbon substrates. We performed tetrazolium dye assays to assess the ability of wild-type (WT) C. thermocellum (strain LL1004) to transport and metabolize 190 different substrates and identified 18 positive hits and 27 false positives. These findings guided the selection of 22 substrates for batch fermentations of WT on 10 g/L alternative substrate plus 1 g/L cellobiose. We identified eight substrates that were either fully or partially consumed (cellobiose, glucose, fructose, sorbitol, arbutin, turanose, pyruvate, glucose-6-phosphate), two that were interconverted (malate, fumarate), seven that may undergo conversion to unidentified fermentation products (xylose, sorbose, tagatose, galactose, mannose, rhamnose, fucose), and five that were not consumed (glycerol, acetate, lactate, propionate, xylitol). Sorbitol and pyruvate, which are more and less reduced than cellobiose, respectively, were selected for further analysis of their effects on redox balance and product formation. Batch fermentations on sorbitol and pyruvate demonstrated that ethanol production in C. thermocellum may be limited in part by the availability of reducing equivalents. Collectively, this work demonstrates the utility of alternative carbon substrates as a tool for perturbing metabolism, redox balance, and fermentation product distributions to further our understanding of the metabolism of anaerobic, thermophilic bacteria such as C. thermocellum for the production of biofuels and biochemicals of interest.