Advances in the synthesis of biobutanol by consolidated bioprocessing from lignocellulose / 生物工程学报

Consolidated bioprocessing (CBP) is a multi-step process in a bioreactor, which completes hydrolase production, enzymatic hydrolysis, and microbial fermentation. It is considered to be the most promising process for the production of second-generation biofuels because of its simple steps and low cost. Due to the complexity of lignocellulose degradation and the butanol synthesis pathway, few wild microorganisms can directly utilize lignocellulose to synthesize butanol. With the development of synthetic biology, single-bacterium directly synthesizes butanol using lignocellulose by introducing a butanol synthesis pathway in the cellulolytic Clostridium. However, there are still some problems such as heavy metabolic load of single bacterium and low butanol yield. Co-culture can relieve the metabolic burden of single bacterium through the division of labor in different strains and can further improve the efficiency of butanol synthesis. This review analyzes the recent research progress in the synthesis of biobutanol using lignocellulose by consolidated bioprocessing from both the single-bacterium strategy and co-culture strategy, to provide a reference for the research of butanol and other biofuels.

Enhanced biobutanol production by optimization of the medium from Clostridium acetobutylicum MTCC 11274 using macroalgae Gracilaria edulis

Clostridial strain Clostridium acetobutylicum MTCC 11274 was employed for producing biobutanol inbatch culture fermentation. The effects of various carbon sources, i.e., xylose, starch, dextrin, glucose, andmannose as well as nitrogen sources, i.e., yeast extract, peptone, beef extract, and soya protein were studiedconventionally (one-factor-at-a-time). It was found that the maximum amount of biobutanol, i.e., 6.27 and 7.40g/l was obtained from 60 g/l glucose and 5 g/l yeast extract, respectively. In addition to this, the interactionsbetween pH, temperature, and glucose concentration were also taken into consideration for the optimization ofbiobutanol production with the help of Central Composite Design (CCD) of Response Surface Methodology.CCD design was used for the optimization of the above-mentioned parameters and low and high values ofvariables were chosen by performing the steepest ascent experiment. The analysis of variance (ANOVA)model was used for estimating the significance of the model coefficients. ANOVA revealed that the modelwas significant (p < 0.05) and the effects of the glucose concentration, pH, and temperature on biobutanolproduction were significant. It was found that 8.56 g/l biobutanol was produced under optimum fermentationconditions with 40 g/l Gracilaria edulis supplemented with 20 g/l glucose as a carbon source

Studies on effect of alkali pretreatment of banana pseudostem for fermentable sugar production for biobutanol production

Aim: In this study, effectiveness of alkali pretreatment of banana pseudostem for the production of biobutanol by fermentation using Clostridium sporogenes under strict anaerobic conditions was studied. Methodology: Banana pseudostem was pretreated by alkali soaking at constant temperature (30, 50 and 70°C) and concentration of 0.25 to 2% (w/v) at solid to liquid ratio of 1:10 for 24 hr to depolymerize the lignocellulosic biomass. Further to increase delignification, the alkali soaked samples were subjected to thermal treatment at 121°C for 15 min. The hydrolysates were subjected to acetone-butanol-ethanol fermentation using Clostridium sporogenes to produce butanol. Results: Maximum delignification of 92% was obtained at 30°C soaking temperature with 2% NaOH (w/v). Increase in temperature led to increase in delignification but also resulted in reduced recovery of cellulose. Maximum glucose yield of 524 mg g-1 glucan was obtained from the pretreated biomass. Fermentation of hydrolysate obtained from alkali soaking pretreatment by C. sporogenes under anaerobic condition resulted in 10.12 g l-1 of butanol with a yield of 0.326 g g-1 of total sugar consumed and it was much higher compared to untreated biomass. Interpretation: Alkali soaking pretreatment at 30°C and alkali concentration of 1.5% (w/v) was effective to depolymerize the biomass to obtain maximum sugar and butanol yield from banana pseudostem. Thermal treatment was not effective in increasing the production of butanol due to pseudo lignin formation and presence of inhibitors.

Evaluation of biobutanol production by Clostridium beijerinckii NRRL B-592 using sweet sorghum as carbon source / Avaliação da produção de biobutanol por Clostridium beijerinckii NRRL B-592 usando sorgo sacarino como fonte de carbono

In this research it was evaluated the production of biobutanol by Clostridium beijerinckiiNRRL B-592 using sweet sorghum juice as carbon source. Operational variables, like pH and initial inoculum size, as well as supplementation of industrial media with yeast extract and tryptone, were evaluated. The maximum butanol obtained was 2.12g kg^-1 using 12.5% of inoculum size, 0.05g 100mL^-1 of tryptone and 0.1g 100mL^-1 of yeast extract and initial pH of 5.5. The main contribution of this research was to show a systematic procedure for development of a low cost industrial media for biobutanol production from sweet sorghum.

Neste trabalho, foi avaliada a produção de biobutanol por Clostridium beijerinckiiNRRL B-592 usando o caldo de sorgo sacarino como fonte de carbono. Foram avaliadas as variáveis operacionais como pH e densidade de inóculo, bem como a suplementação de meios industriais com extrato de levedura e triptona. A máxima concentração de butanol obtida foi de 2,12g kg^-1, utilizando 12,5% de inóculo, 0,05g 100mL^-1 de triptona e 0,1g 100ml^-1 de extrato de levedura e pH inicial de 5,5. A principal contribuição deste trabalho foi o de mostrar um procedimento sistemático para o desenvolvimento de um meio industrial de baixo custo para a produção de biobutanol a partir de sorgo sacarino.