Abstract
Hexanol–butanol–ethanol fermentation from syngas by Clostridium carboxidivorans P7 is a promising route for biofuel production. However, bacterial agglomeration in the culture of 37 °C severely hampers the accumulation of biomass and products. To investigate the effect of culture temperature on biomass growth and higher-alcohol production, C. carboxidivorans P7 was cultivated at both constant and two-step temperatures in the range from 25 to 37 °C. Meanwhile, Tween-80 and saponin were screened out from eight surfactants to alleviate agglomeration at 37 °C. The results showed that enhanced higher-alcohol production was contributed mainly by the application of two-step temperature culture rather than the addition of anti-agglomeration surfactants. Furthermore, comparative transcriptome revealed that although 37 °C promoted high expression of genes involved in the Wood–Ljungdahl pathway, genes encoding enzymes catalyzing acyl-condensation reactions associated with higher-alcohol production were highly expressed at 25 °C. This study gained greater insight into temperature-effect mechanism on syngas fermentation by C. carboxidivorans P7.
Highlights
Biofuel production is developed as a sustainable alternative to deal with the global demand of energy due to diminishing fossil fuel reserves and increasing greenhouse gases generated from using fossil fuels (Latif et al 2014)
Clostridium carboxidivorans P7 is one of model organisms widely studied for hexanol–butanol–ethanol fermentation from syngas, it employs the Wood–Ljungdahl pathway (WL pathway) to convert CO or CO2 into acetylCoA, and produces two–six carbon chain (C2–Six-carbon chain (C6)) alcohols and acids (Fernández-Naveira et al 2017b)
Effect of CT culture on growth and production As shown in Fig. 1a, the growth of C. carboxidivorans P7 was observed in the range from 25 to 37 °C, which fully confirmed that C. carboxidivorans P7 had a good adaptability to temperature (Fernández-Naveira et al 2017a; Latif et al 2014)
Summary
Biofuel production is developed as a sustainable alternative to deal with the global demand of energy due to diminishing fossil fuel reserves and increasing greenhouse gases generated from using fossil fuels (Latif et al 2014). As one of emerging production approaches, syngas fermentation utilizes acetogens to fix carbon-containing gas to biofuel, which accommodates numerous sources of raw materials, including industrial, agricultural and municipal wastes (Ramachandriya et al 2013). A wide range of carbon-containing materials can be first converted into syngas which can indistinguishably be used by gas-fermenting microbes. Clostridium carboxidivorans P7 is one of model organisms widely studied for hexanol–butanol–ethanol fermentation from syngas, it employs the Wood–Ljungdahl pathway (WL pathway) to convert CO or CO2 into acetylCoA, and produces two–six carbon chain (C2–C6) alcohols and acids (Fernández-Naveira et al 2017b). Higher-alcohols (designated as butanol and hexanol in this study) have featured with superb fuel characteristics more than higher energy
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