拜氏梭菌13-2发酵甘蔗渣水解液生产丁醇的研究

目的:蔗渣是一种重要的可再生生物质资源,蔗渣原料生产丁醇将大大降低丁醇的成本.方法:实验利用0.25 ～3.0%不同浓度稀H2SO4对蔗渣进行121℃的高温作用1h,以水解液为碳源,进行丁醇的发酵实验.结果:相对于8052菌株,13 -2菌株对甘蔗渣水解液具有更高的发酵效率,在0.5%硫酸用量条件下,13 -2菌株的丁醇发酵量最高,达到4.5g/L.而8052只有2.3g/L的丁醇发酵量.结论:在同等条件下,拜氏梭菌菌株13 -2比模式菌株8052具有更高的溶剂产量和抑制物耐受能力,最佳的蔗渣水解条件为1.5%硫酸用量,丁醇发酵量和总溶剂分别为4.57g/L和5.41 g/L.     

An approach to cellulase recovery from enzymatic hydrolysis of pretreated sugarcane bagasse with high lignin content

The possibility of recovering the cellulases used for enzymatic hydrolysis of sugarcane bagasse was evaluated. A strategy was adopted to maximize the enzyme recovery: desorption of the enzymes adsorbed in the solid residue after hydrolysis, and re-adsorption of the enzymes from the liquid medium onto a fresh substrate. The use of surfactant during the enzymatic hydrolysis was important to improve the glucose release from the material structure and also to facilitate the enzyme desorption from the solid residue after hydrolysis. The temperature and pH used during desorption influenced the enzymes recovery, with the best results (90% adsorbed cellulase) being achieved at 45?°C and pH 5.5. The enzymes present in the liquid medium after enzymatic hydrolysis were partially recovered (77%) by adsorption onto the fresh substrate and used in new enzymatic hydrolysis batches. It was concluded that it is possible to recycle cellulases from an enzymatic medium for use in subsequent hydrolysis processes.     

Trans-3-Methylthioacrylamide,a New Metabolic Product from Streptomyces sioyaensis

Rhodosporidium toruloides is a lipid-producing yeast, the growth of which is severely suppressed when hydrolysates of lignocellulosic biomass are used as carbon source. This is probably due to the toxic substances, such as organic acids, furans, and phenolic compounds produced during the preparation of the hydrolysates. In order to solve this problem, R. toruloides cultures were subjected to atmospheric room-temperature plasma mutagenesis, resulting in the isolation of mutants showing tolerance to sugarcane bagasse hydrolysate (SBH). Three mutant strains, M11, M13, and M18, were found to grow with producing lipids with SBH as carbon source. M11 in particular appeared to accumulate higher levels (up to 60% of dry cell weight) of intracellular lipids. Further, all three mutant strains showed tolerance of vanillin, furfural, and acetic acid, with different spectra, suggesting that different genetic determinants are involved in SBH tolerance.     

Streptomyces thermocerradoensis I3 secretes a novel bifunctional xylanase/endoglucanase under solid-state fermentation

Lignocellulosic wastes can be potentially converted into several bioproducts such as glucose, xylo-oligosaccharides, and bioethanol. Certain processes, such as enzymatic hydrolysis, are generally needed to convert biomass into bioproducts. The present study investigated the production of xylanases and cellulases by Streptomyces thermocerradoensis I3 under solid-state fermentation (SSF), using wheat bran as a low-cost medium. The activities of xylanase and carboxymethyl cellulase (CMCase) were evaluated until 96 hr of incubation. The highest enzyme activity was observed after 72 hr of incubation. The crude enzyme extract was sequentially filtered, first using a 50 kDa filter, followed by a 30 kDa filter. Fraction 3 (F3) exhibited activities of both xylanase and CMCase. Xylanase and CMCase showed optimum activity at 70°C and pH 6.0 and 55°C and pH 6.0, respectively. The zymogram analysis showed a single activity band with a molecular mass of approximately 17 kDa. These findings provide strong evidence that the enzyme is a bifunctional xylanase/endoglucanase. This enzyme improved the saccharification of sugarcane bagasse by 1.76 times that of commercial cellulase. This enzyme has potential applications in various biotechnological procedures.     

Optimization of sugarcane bagasse conversion by hydrothermal treatment for the recovery of xylose

This work aims at the valorization of sugarcane bagasse by extracting xylose which is destined to the production of xylitol after purification and hydrogenation. Our approach consists in applying the principle of biorefinery to sugarcane bagasse because of its hemicellulose composition (particularly rich in xylan: (92%)). Optimizing of the thermal treatment was investigated. A treatment at 170 °C for 2 h was found optimal, with higher solubilzation of hemicellulose than that at 150 °C and lower degradation of sugar monomers than 190 °C. Recovery of xylose was high and the purity of xylose solution (78%) allows expecting an easy purification and separation of xylose before hydrogenation. Analysis of thermal hydrolyzates shows the presence of xylan oligomers and polymers with large distribution of DPs. This fraction should be submitted to enzymatic treatment to recover more xylose monomer.     

Cassava bagasse cellulose nanofibrils reinforced thermoplastic cassava starch

Cellulose cassava bagasse nanofibrils (CBN) were directly extracted from a by-product of the cassava starch (CS) industry, viz. the cassava bagasse (CB). The morphological structure of the ensuing nanoparticles was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), presence of other components such as sugars by high performance liquid chromatography (HPLC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) experiments. The resulting nanofibrils display a relatively low crystallinity and were found to be around 2–11 nm thick and 360–1700 nm long. These nanofibrils were used as reinforcing nanoparticles in a thermoplastic cassava starch matrix plasticized using either glycerol or a mixture of glycerol/sorbitol (1:1) as plasticizer. Nanocomposite films were prepared by a melting process. The reinforcing effect of the filler evaluated by dynamical mechanical tests (DMA) and tensile tests was found to depend on the nature of the plasticizer employed. Thus, for the glycerol-plasticized matrix-based composites, it was limited especially due to additional plasticization by sugars originating from starch hydrolysis during the acid extraction. This effect was evidenced by the reduction of glass vitreous temperature of starch after the incorporation of nanofibrils in TPSG and by the increase of elongation at break in tensile test. On the other hand, for glycerol/sorbitol plasticized nanocomposites the transcrystallization of amylopectin in nanofibrils surface hindered good performances of CBN as reinforcing agent for thermoplastic cassava starch. The incorporation of cassava bagasse cellulose nanofibrils in the thermoplastic starch matrices has resulted in a decrease of its hydrophilic character especially for glycerol plasticized sample.     

Genome shuffling improves production of cellulase by Penicillium decumbens JU‐A10

Aims: Improvement of cellulase production of Penicillium decumbens by genome shuffling of an industrial catabolite‐repression‐resistant strain JU‐A10 with its mutants. Methods and Results: After two rounds of genome shuffling, three fusants, GS2‐15, GS2‐21 and GS2‐22, were obtained, showing 100%, 109% and 94% increase in FPase activity than JU‐A10 respectively. The cellulase production of the fusants on various substrates, such as corn stover, wheat straw, bagasse and the corncob residue, was studied. The maximum productivities of GS2‐15, GS2‐21 and GS2‐22 were 92·15, 102·63 and 92·35 FPU l^?1 h^?1 on the corncob residue at 44 h respectively, which were 117%, 142% and 118% higher than that of JU‐A10 (42·44 FPU l^?1 h^?1, at 90 h). The improvements of the fusants were possibly because of their enhanced growth rates, earlier cellulase synthesis and higher secretion of extracellular proteins. Conclusions: The fusants obtained after genome shuffling could produce abundant cellulase much earlier, and they could be potential candidates for bioconversion process. Significance and Impact of the Study: This is the first report on the improvement of cellulase production in fungi by genome shuffling, and this is a good technique to improve other important phenotypes in fungi.     

Image analysis of modified cellulose fibers from sugarcane bagasse by zirconium oxychloride

Surface modification of natural fibers has been made using different methods. In this paper, cellulose fibers from sugarcane bagasse were bleached and modified by zirconium oxychloride in situ. The chemically modified cellulose fibers were compared to those of bleached ones. Cellulose fibers were modified with ZrO₂·nH₂O nanoparticles through the use of zirconium oxychloride in acidic medium in the presence of cellulose fibers using urea as the precipitating agent. The spatial distribution characterization of hydrous zirconium oxide on cellulose fibers was carried out by combining both processing and image analyses obtained by SEM and statistical methodologies. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TG) were also used to characterize the nanocomposite. Results indicated that ZrO₂·nH₂O nanoparticles of about 30-80 nm diameter deposited on cellulose fibers were heterogeneously dispersed.     

The influence of pH and dilution rate on continuous production of xylitol from sugarcane bagasse hemicellulosic hydrolysate by C. guilliermondii

Continuous fermentation of sugarcane bagasse hemicellulosic hydrolysate by the yeast Candida guilliermondii FTI 20037 was used for xylitol production from xylose. Experiments were carried out in a reactor with 1.25 l of treated hydrolysate, at 30 °C and 300 rpm. A 2² full-factorial central composite design was employed for experimental study and analysis of the results. A statistical analysis of the results showed that the effects of the pH and dilution rate (D), the interactions between these variables and the second-order effect of D on the xylitol volumetric productivity (Q_p) were significant at a 95% confidence level. The second-order effect of pH was also significant at a 90% confidence level. The k_La effect on the Q_p was not significant. A volumetric productivity of 0.68 g/l h, representing 95.8% of the predicted value (0.72 g/l h), was obtained.     

Aroma compounds produced by Kluyveromyces marxianus in solid state fermentation on a packed bed column bioreactor

Studies were carried out for the production of aroma compounds by Kluyveromyces marxianus grown on cassava bagasse in solid state fermentation using packed bed reactors, testing two different aeration rates. Respirometric analysis was used to follow the growth of the culture. Headspace analysis of the culture by gas chromatography showed the production of 11 compounds, out of which nine were identified. Ethyl acetate, ethanol and acetaldehyde were the major compounds produced. Lower aeration rate (0.06l h^–1 g^–1 of initial dry matter) increased total volatile (TV) production and the rate of production was also increased at this aeration rate. Using an aeration rate of 0.06l h^–1 g^–1 maximum TV concentrations were reached at 24 h and at 40 h with 0.12l h^–1 g^–1.