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The biomass obtained after the extraction of forskolin from the roots of Coleus forskohlii was evaluated as a substrate for the production of acetone-butanol-ethanol (ABE). The spent biomass constituting more than 90% of the raw material showed 50–70% carbohydrates with starch and cellulose being the major constituents. This study was undertaken to optimize enzymatic hydrolysis of C. forskohlii roots for maximum release of fermentable sugars and subsequent fermentation to ABE. The root biomass was hydrolyzed using the Stargen ® 002 and Accellerase ® 1500. Cocktail of both enzymes (16U Stargen ® 002 and 60 FPU Accellerase ® 1500) could produce 41.2 g/l of total reducing sugars (glucose equivalent to 32.33 g/l). The production of ABE was optimized in a batch fermentation using Clostridium acetobutylicum NCIM 2877. The maximum ABE production using the root hydrolysates was 0.55 g/l. Pretreatment with lime and Amberlite XAD-4 increased the production of total solvent to 5.33 g/l. [ABSTRACT FROM AUTHOR]

Acetone being a non-fuel solvent produced during the traditional acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum ; reduces the overall fuel alcohol yield. However, the conversion of acetone into isopropanol has been recommended to improve the process economy. The present study aims to develop an engineered C. acetobutylicum DSM 792 strain to convert acetone into isopropanol by introducing the secondary alcohol dehydrogenase gene from Clostridium beijerinckii NRRL B593 using the allele-coupled exchange approach. Batch and continuous fermentation experiments were carried out with a modified strain C. acetobutylicum DSM 792-ADH to improve the isopropanol yield and titer. The growth and production behavior of the modified strain in stationary flask culture and controlled batch culture was studied. Almost 50% of acetone was converted into isopropanol with highest total solvent yield to be 0.39 g g −1 glucose. The modified strain also utilized sugar mixture and SO 2 –ethanol–water spent liquor as a substrate to produce the solvents. [ABSTRACT FROM AUTHOR]

The co-production of acetone during traditional butanol fermentation (acetone–butanol–ethanol) lowers the yield of alcohol biofuels. The present study was aimed to develop an improved Clostridium acetobutylicum strain with enhanced alcohol fuel production capability. The previously developed IBE (isopropanol-butanol-ethanol) producing C. acetobutylicum DSM792-ADH strain was further optimized to enhance the solvent productivity and yield. Immobilized cell column reactor was used to investigate the effect of dilution rate on IBE fermentation. Pure glucose, artificial sugar mixture and SEW spent liquor from spruce chips were used as substrates to study the behavior of the modified microorganism. The highest total solvent concentrations of approximately 10.60 g l −1 , 10 g l −1 and 6 g l −1 were obtained when glucose, sugar mixture and SEW spent liquor were used as substrates respectively. The modified microorganism could effectively utilize the lignocellulosic biomass hydrolyzate (SEW spent liquor) to yield a solvent productivity of 1.67 g l −1 h −1 . [ABSTRACT FROM AUTHOR]

• ABE solventogenesis with reducing agents and controlled feeding regimen. • L-cysteine and DTT fed-batches achieved solvent yield of 0.38 and 0.37 g/g. • 24.33 and 22.98 g/L of ABE produced by L-cysteine and DTT fed-batches. • Enhanced solventogenesis led to higher ATP levels in DTT and L-cysteine batches. • Histidine secretion is important in Clostridial acid stress. Acetone-butanol-ethanol (ABE) fermentation process is a promising bioenergy option amid rising concerns over the environmental impact of fossil fuel usage. However, the commercialization of the ABE process has been marred by challenges of low product yield and titer, thereby non-competitive process economics. Here, we coupled cost competitive reducing agents with a controlled feeding strategy to improve both product titer and yield. Reducing agents promote cofactor dependent butanol production, while fed-batch operation enhances glucose consumption, final ABE titer, and partly mitigates product toxicity. The effects of ascorbic acid, L-cysteine, and dithiothreitol (DTT) on ABE fed-batch production using Clostridium acetobutylicum was investigated in current study. NADH, ATP, extracellular amino acid secretion, and NADH-dependent butanol dehydrogenase (BDH) assays were performed to study the metabolic modifications triggered by reducing agents. Incidentally, L-cysteine and DTT improved ABE solvent titer by 2-fold, producing 24.33 and 22.98 g/L ABE with solvent yields of 0.38 and 0.37 g/g, respectively. Elevated NADH, BDH, and ATP levels in fermentation broth reflected in enhanced ABE titer and yield. Furthermore, histidine secretion emerged as an important factor in Clostridial acid stress tolerance in this study. The results demonstrate that addition of reducing agents in fed-batch ABE fermentation operation enables efficient utilization of glucose with significant improvement in solvent production. [ABSTRACT FROM AUTHOR]