Cultivation of a new butanol-acetone producing clostridium species strain G33

Abstract

The global energy crisis has renewed interest in producing alternative liquid fuels from clean, renewable sources, e.g., generation of biofules via biological processes. In this study, a Clostridium sp. strain G33 was obtained with soil inoculum from grassland in Singapore, which is capable of producing dominant butanol from monosugars (e.g., glucose and xylose). The 16S rRNA gene of strain G33 shows 99% identity with Clostridium sp. strain 8052, while both strains possess the ability to produce biosolvents such as acetone and butanol. In the presence of 30 g/L glucose, culture G33 could produce 8.60 g/L butanol in batch cultures with a butanol-to-acetone ratio of 2.7:1 and a butanol yield of 29%, the yield of which is the highest comparing with previous reported strain at similar conditions. No ethanol was detected during the fermentation, implying a simplified purification process of the products (butanol and acetone as end-products) in contrast to that of typical Clostridium strains (acetone, butanol and ethanol as end-products). Butanol dehydrogenase (bdh) was found to be the functional gene responsible for butanol production. Interestingly, strain G33 could utilize xylan to produce hydrogen and fatty acids under mesophilic conditions, while most clostridium could only feed on simple sugars. When supplemented with 10 g/L xylan, culture G33 generated ∼1.4 mmol hydrogen and ∼10 mM butyric acid. Direct utilization of hemicellulosic feedstock by culture G33 provides advantages over the traditional physicochemical pretreatment and enzymatic hydrolysis. Therefore, culture G33 shows potential to convert the renewable lignocellulosic biomass into biofuels and serves as a candidate for industrial butanol production.