Artificial symbiosis for acetone-butanol-ethanol (ABE) fermentation from alkali extracted deshelled corn cobs by co-culture of Clostridium beijerinckii and Clostridium cellulovorans

Abstract

BackgroundButanol is an industrial commodity and also considered to be a more promising gasoline substitute compared to ethanol. Renewed attention has been paid to solvents (acetone, butanol and ethanol) production from the renewable and inexpensive substrates, for example, lignocellulose, on account of the depletion of oil resources, increasing gasoline prices and deteriorating environment. Limited to current tools for genetic manipulation, it is difficult to develop a genetically engineered microorganism with combined ability of lignocellulose utilization and solvents production. Mixed culture of cellulolytic microorganisms and solventogenic bacteria provides a more convenient and feasible approach for ABE fermentation due to the potential for synergistic utilization of the metabolic pathways of two organisms. But few bacteria pairs succeeded in producing biobutanol of high titer or high productivity without adding butyrate. The aim of this work was to use Clostridium cellulovorans 743B to saccharify lignocellulose and produce butyric acid, instead of adding cellulase and butyric acid to the medium, so that the soluble sugars and butyric acid generated can be subsequently utilized by Clostridium beijerinckii NCIMB 8052 to produce butanol in one pot reaction.ResultsA stable artificial symbiotic system was constructed by co-culturing a celluloytic, anaerobic, butyrate-producing mesophile (C. cellulovorans 743B) and a non-celluloytic, solventogenic bacterium (C. beijerinckii NCIMB 8052) to produce solvents by consolidated bioprocessing (CBP) with alkali extracted deshelled corn cobs (AECC), a low-cost renewable feedstock, as the sole carbon source. Under optimized conditions, the co-culture degraded 68.6 g/L AECC and produced 11.8 g/L solvents (2.64 g/L acetone, 8.30 g/L butanol and 0.87 g/L ethanol) in less than 80 h. Besides, a real-time PCR assay based on the 16S rRNA gene sequence was performed to study the dynamics of the abundance of each strain during the co-culturing process, which figured out the roles of each strain at different periods in the symbiosis.ConclusionOur work illustrated the great potential of artificial symbiosis in biofuel production from lignocellulosic biomass by CBP. The dynamics of the abundance of C. beijerinckii and C. cellulovorans revealed mechanisms of cooperation and competition between the two strains during the co-culture process.

Microalgae Oil: Algae Cultivation and Harvest, Algae Residue Torrefaction and Diesel Engine Emissions Tests

“…Ethanol has previously been used in diesel engines but poses challenges such as low cetane number, reduced viscosity and calorific value of its blends (Rakopoulos et al, 2011). Butanol is the main product of the ABE process and apparently in contrast to other alcohols has superior qualities that make an easy pick for blending with diesel such as less hydrophilicity, easy miscibility, higher cetane value, less volatile, higher heating values and its energy density is similar to gasoline's (Wen et al, 2014). Furthermore butanol apart from being as a fuel it is used in the food, plastic and specialty industries (Tran et al, 2010).…”

“…ABE fermentation process depends on cellulosic sources as substrates. Initially, the substrates included carbohydrate rich feedstock such as bagasse, rice straw, cassava, molasses, palm fiber, maize, potatoes, beets or even domestic wastes (Claassen et al, 2000;Ponthein and Cheirsilp, 2011;Wen et al, 2014). The solventogenic activity of anaerobic Clostridium bacteria strains drives the ABE fermentation process (Maddox et al, 1995).…”

Advances in consolidated bioprocessing systems for bioethanol and butanol production from biomass: a comprehensive review

“…strain BOH3). Wen et al, (2014a) successfully used a co-culture system for CBP production of butanol from alkali-pretreated deshelled corn cobs. They used a cellulolytic, anaerobic, butyrate-producing mesophilic C. cellulovorans strain 743B to hydrolyze pre-treated corn cob and produce butyric acid.…”

“…It has an energy content that is similar to gasoline, so, less volume is required than ethanol to achieve the same energy output. Butanol has a lower vapor pressure compared to ethanol, and is therefore safer during transport and use in car engines (Ezeti and Blaschek, 2007;Ni and Sun, 2009;Quershi et al, 2013;Wen et al, 2014a).…”

“…In another study, by using a microbial consortium containing C. thermosuccinogene, C. straminisolvens and C. isatidis, Du et al (2010) . 0.5 g/l filter paper and produce 1.54 g/l ethanol within 3 d. Wen et al (2014a) used a microbial consortium containing a cellulolytic, anaerobic, butyrateproducing mesophile (C. cellulovorans 743B) to saccharify lignocellulose and produce butyric acid, and a non-cellulolytic, solventogenic bacterium (C. beijerinckii NCIMB 8052) to produce butanol and ethanol from alkali extracted deshelled corn cobs in one pot reaction. After optimizing the coculture conditions, 11.8 g/l solvents (2.64 g/l acetone, 8.30 g/l butanol and 0.87 g/l ethanol) was achieved from 68.6 g/l degraded corn cobs in less than 80 h. In another work, Wen et al (2014b) by subsequential co-culturing of C. thermocellum ATCC 27405 and C. beijerinckii NCIMB 8052 and using combinatorial optimal culture parameters for sugars accumulation and ABE production, could improve the yield up to 19.9 g/l (acetone 3.96, butanol 10.9 and ethanol 5.04 g/l) after 200 h.…”