Search Results (3)

Different strategies have been assessed for the revalorization of guishe to obtain biomolecules. The juice obtained after the mechanical extraction of guishe is rich in phytochemicals and sugars which can be converted to other products. The objective of the present study was to evaluate the production of hydrogen and butanol at different guishe juice concentrations (and therefore, different sugar concentrations) via fermentation in batch mode using Clostridium acetobutylicum ATCC 824. Fermentation assays were performed in triplicate under anaerobic conditions at 35 °C for 142 h. Guishe juice was supplemented with all components of synthetic medium (salts, vitamins and reducing agents), except glucose, and diluted at different concentrations: 20%, 40%, 60%, 80% and 100%. For comparison purposes, a control was carried out in a synthetic medium using glucose as carbon source. Results showed a maximum butanol concentration of 5.39 g/L using 80% guishe juice, corresponding to a productivity and yield of 0.04 g/L h⁻¹ and 0.24 g/g, respectively. Meanwhile, the highest productivity (1.16 L H₂/L d⁻¹; 1.99 mmol H₂/L h⁻¹) and yield (18.4 L/kg) of hydrogen were obtained with 40% guishe juice. This study demonstrates the potential of guishe juice to be used as a low-cost substrate for hydrogen and butanol production. Full article

This study was conducted in order to optimise simultaneous saccharification and fermentation (SSF) for biobutanol production from a pretreated oil palm empty fruit bunch (OPEFB) by Clostridium acetobutylicum ATCC 824. Temperature, initial pH, cellulase loading and substrate concentration were screened using one factor at a time (OFAT) and further statistically optimised by central composite design (CCD) using the response surface methodology (RSM) approach. Approximately 2.47 g/L of biobutanol concentration and 0.10 g/g of biobutanol yield were obtained after being screened through OFAT with 29.55% increment (1.42 fold). The optimised conditions for SSF after CCD were: temperature of 35 °C, initial pH of 5.5, cellulase loading of 15 FPU/g-substrate and substrate concentration of 5% (w/v). This optimisation study resulted in 55.95% increment (2.14 fold) of biobutanol concentration equivalent to 3.97 g/L and biobutanol yield of 0.16 g/g. The model and optimisation design obtained from this study are important for further improvement of biobutanol production, especially in consolidated bioprocessing technology. Full article

Clostridium acetobutylicum has traditionally been used for production of acetone, butanol, and ethanol (ABE). Butanol is a commodity chemical due in part to its suitability as a biofuel; however, the current yield of this product from biological systems is not economically feasible as an alternative fuel source. Understanding solvent phase physiology, solvent tolerance, and their genetic underpinning is key for future strain optimization of the bacterium. This study shows the importance of a [NiFe]-hydrogenase in solvent phase physiology. C. acetobutylicum genes ca_c0810 and ca_c0811, annotated as a HypF and HypD maturation factor, were found to be required for [NiFe]-hydrogenase activity. They were shown to be part of a polycistronic operon with other hyp genes. Hydrogenase activity assays of the ΔhypF/hypD mutant showed an almost complete inactivation of the [NiFe]-hydrogenase. Metabolic studies comparing ΔhypF/hypD and wild type (WT) strains in planktonic and sessile conditions indicated the hydrogenase was important for solvent phase metabolism. For the mutant, reabsorption of acetate and butyrate was inhibited during solventogenesis in planktonic cultures, and less ABE was produced. During sessile growth, the ΔhypF/hypD mutant had higher initial acetone: butanol ratios, which is consistent with the inability to obtain reduced cofactors via H₂ uptake. In sessile conditions, the ΔhypF/hypD mutant was inhibited in early solventogenesis, but it appeared to remodel its metabolism and produced mainly butanol in late solventogenesis without the uptake of acids. Energy filtered transmission electron microscopy (EFTEM) mapped Pd(II) reduction via [NiFe]-hydrogenase induced H₂ oxidation at the extracelluar side of the membrane on WT cells. A decrease of Pd(0) deposits on ΔhypF/hypD comparatively to WT indicates that the [NiFe]-hydrogenase contributed to the Pd(II) reduction. Calculations of reaction potentials during acidogenesis and solventogenesis predict the [NiFe]-hydrogenase can couple NAD⁺ reduction with membrane transport of electrons. Extracellular oxidation of H₂ combined with the potential for electron transport across the membrane indicate that the [NiFe}-hydrogenase contributes to proton motive force maintenance via hydrogen cycling. Full article