Abstract
BackgroundClostridium thermocellum is a cellulolytic anaerobic thermophile that is a promising candidate for consolidated bioprocessing of lignocellulosic biomass into biofuels such as ethanol. It was previously shown that expressing Thermoanaerobacterium saccharolyticum adhA in C. thermocellum increases ethanol yield.In this study, we investigated expression of adhA genes from different organisms in Clostridium thermocellum.MethodsBased on sequence identity to T. saccharolyticum adhA, we chose adhA genes from 10 other organisms: Clostridium botulinum, Methanocaldococcus bathoardescens, Thermoanaerobacterium ethanolicus, Thermoanaerobacter mathranii, Thermococcus strain AN1, Thermoanaerobacterium thermosaccharolyticum, Caldicellulosiruptor saccharolyticus, Fervidobacterium nodosum, Marinitoga piezophila, and Thermotoga petrophila. All 11 adhA genes (including T. saccharolyticum adhA) were expressed in C. thermocellum and fermentation end products were analyzed.ResultsAll 11 adhA genes increased C. thermocellum ethanol yield compared to the empty-vector control. C. botulinum and T. ethanolicus adhA genes generated significantly higher ethanol yield than T. saccharolyticum adhA.ConclusionOur results indicated that expressing adhA is an effective method of increasing ethanol yield in wild-type C. thermocellum, and that this appears to be a general property of adhA genes.
Highlights
Clostridium thermocellum is a cellulolytic anaerobic thermophile that is a promising candidate for consolidated bioprocessing of lignocellulosic biomass into biofuels such as ethanol
Clostridium thermocellum is a cellulolytic anaerobic thermophile that is considered to be a promising candidate for consolidated bioprocessing of lignocellulosic biomass, into biofuels such as ethanol, due to its native ability to solubilize lignocellulose [1]
Strategies to increase ethanol yield in C. thermocellum include deleting the pathways for acetic acid, lactic acid, and hydrogen production [3,4,5,6], and introducing heterologous genes from ethanol production pathways in other organisms [2, 7], such as Thermoanaerobacterium saccharolyticum
Summary
Clostridium thermocellum is a cellulolytic anaerobic thermophile that is a promising candidate for consolidated bioprocessing of lignocellulosic biomass into biofuels such as ethanol. It was previously shown that expressing Thermoanaerobacterium saccharolyticum adhA in C. thermocellum increases ethanol yield.In this study, we investigated expression of adhA genes from different organisms in Clostridium thermocellum. Clostridium thermocellum is a cellulolytic anaerobic thermophile that is considered to be a promising candidate for consolidated bioprocessing of lignocellulosic biomass, into biofuels such as ethanol, due to its native ability to solubilize lignocellulose [1]. Strategies to increase ethanol yield in C. thermocellum include deleting the pathways for acetic acid, lactic acid, and hydrogen production [3,4,5,6], and introducing heterologous genes from ethanol production pathways in other organisms [2, 7], such as Thermoanaerobacterium saccharolyticum.
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