Fuying Ma

Combination of biological pretreatment with mild acid pretreatment for enzymatic hydrolysis and ethanol production from water hyacinth.

The mild acid pretreatment and the combination of biological pretreatment by a white rot fungus Echinodontium taxodii or a brown rot fungus Antrodia sp. 5898 with mild acid pretreatment were evaluated under different pretreatment conditions for enzymatic hydrolysis and ethanol production from water hyacinth. The combined pretreatment with E. taxodii (10 days) and 0.25% H(2)SO(4) was proved to be more effective than the sole acid pretreatment. The reducing sugar yield from enzymatic hydrolysis of co-treated water hyacinth increased 1.13-2.11 fold than that of acid-treated water hyacinth at the same conditions. The following study on separate hydrolysis and fermentation with Saccharomyces cerevisiae indicated that the ethanol yield from co-treated water hyacinth achieved 0.192 g/g of dry matter, which increased 1.34-fold than that from acid-treated water hyacinth (0.146 g/g of dry matter). This suggested that the combination of biological and mild acid pretreatment is a promising method to improve enzymatic hydrolysis and ethanol production from water hyacinth with low lignin content.

Biological pretreatment of corn stover by Irpex lacteus for enzymatic hydrolysis.

The feasibility of biological pretreatment for subsequent saccharification largely depends upon an effective pretreatment system. A significant enhancement of saccharification was discovered with corn stover pretreated by white rot fungus Irpex lacteus CD2. The highest saccharification ratio reached 66.4%, which was significantly higher than what was reported. Hemicellulose was first destroyed in the process and then lignin. Lignin and hemicellulose were selectively degraded over cellulose, respectively, resulting in increased crystallinity. Enhanced saccharification and the fluctuation in crystallinity together indicated the destruction of the cellulose crystalline structure. Additionally, further studies revealed the disruption of the cell wall and the vital increase of large pores in the pretreated samples, which might be caused by the selective degradation of amorphous components and fungal penetration. Results suggest that I. lacteus has a more efficient degradation system than other reported white rot fungi and can be further explored as an alternative to the existing thermochemical processes.

Lignocellulose degradation and enzyme production by Irpex lacteus CD2 during solid-state fermentation of corn stover

The white rot fungus Irpex lacteus CD2 was incubated on corn stover under solid-state fermentation conditions for different durations, from 5 days up to 120 days. Lignocellulose component loss, enzyme production and Fe3+-reducing activity were studied. The average weight loss ranged from 1.7% to 60.5% during the period of 5-120 days. In contrast to lignin, hemicellulose and cellulose were degraded during the initial time period. After 15 days, 63.0% of hemicellulose was degraded. Cellulose was degraded the most during the first 10 days, and 17.2% was degraded after 10 days. Lignin was significantly degraded and modified, with acid insoluble lignin loss being nearly 80% after 60 days. That weight loss, which was lower than the total component loss, indicated that not all of the lost lignocellulose was converted to carbon dioxide and water, which was indicated by the increase in soluble reducing sugars and acid soluble lignin. Filter paper activity, which corresponds to total cellulase activity, peaked at day 5 and remained at a high level from 40 to 60 days. High hemicellulase activity appeared after 30 days. No ligninases activity was detected during the incipient stage of lignin removal and only low lignin peroxidase activity was detected after 25 days. Apparently, neither of the enzymatic peaks coincided well with the highest amount of component loss. Fe3+-reducing activity could be detected during all the decay periods, which might play an important role in lignin biodegradation by I. lacteus CD2.

Fungal treatment of cornstalks enhances the delignification and xylan loss during mild alkaline pretreatment and enzymatic digestibility of glucan

Fungal treatment with Irpex lacteus was used to enhance the delignification and xylan loss during mild alkaline pretreatment and subsequent enzymatic conversion in this research. The 15-day bio-treatment can modify the lignin structure and increase losses of lignin (from 75.67% to 80.00%) and xylan (from 40.68% to 51.37%) during alkaline pretreatment, making the enzymatic conversion more efficient. The high digestibility of glucan can be obtained after the bio-treatment and alkaline pretreatment at near room-temperature (30 degrees C), and the maximum digestibility increased 14% in comparison with that after the sole alkaline pretreatment. The bio-treatment enhanced delignification and glucan digestibility more significantly when the alkaline pretreatment was performed at lower severity. Additionally, Nuclei Growth model with a time-dependent rate constant can describe well the delignification and xylan loss. Results indicated that the bio-treatment increased the rate constant of initial reaction, but accelerated the decline of rate constant during alkaline pretreatment.

Removal of sulfonamide antibiotics by oriented immobilized laccase on Fe3O4 nanoparticles with natural mediators

A novel strategy was applied in the oriented immobilization of laccase from Echinodontium taxodii on concanavalin A-activated Fe3O4 nanoparticles (GAMNs-Con A) based on laccase surface analysis. These nanoparticles showed higher enzyme loading and activity recovery compared with conventional covalent binding. Along with the improvement in thermal and operational stabilities, the oriented immobilized laccase (GAMNs-Con A-L) exhibited higher substrate affinity than free laccase. Free laccase and GAMNs-Con A-L were then applied in the removal of sulfonamide antibiotics (SAs). Although both free and immobilized laccase resulted in the rapid removal of SAs, GAMNs-Con A-L showed a higher removal rate of SAs compared with the free counterpart in the presence of S-type compounds present in lignin structure. Syringic acid mediated the fastest removal efficiency of SAs among S-type compounds and resulted in an almost complete removal of these substances after incubation for 5min. The oxidation products of SAs were identified via LC-ESI(+)-MS. The results suggested the transformation of SAs and S-type compounds were catalyzed by laccase, resulting in the formation of cross-coupled products.

Effect of biopretreatment on thermogravimetric and chemical characteristics of corn stover by different white-rot fungi

The thermogravimetric and chemical characterization of corn stover biopretreated by three different species of white-rot fungi have been studied in this research. Results indicated that biopretreatment can optimize the thermal decomposition, decrease the reaction temperature and reduce the gas contamination (SO(x)), making the biomass pyrolysis more efficient and environmentally friendly. Biopretreatment can decrease the activation energy and reacting temperature of the hemicellulose and cellulose pyrolysis (up to 36 degrees C), shorten the temperature range of the active pyrolysis (up to 14 degrees C), and increase the thermal decomposition rate, greatly promoting the reaction and making the biomass pyrolysis easier to start and carry on. On the other hand, by biopretreatment, the sulphur content can decrease up to 46.15%, which can considerably reduce the inventory of SO(x) emission. Moreover, the mechanism of the biopretreatment was also explored that the deconstruction and depolymerization of the recalcitrant linkages of lignin and cellulose by biopretreatment can make the structure of biomass incompact and easier to be pyrolyzed.

Expression of the Laccase Gene from a White Rot Fungus in Pichia pastoris Can Enhance the Resistance of This Yeast to H2O2-Mediated Oxidative Stress by Stimulating the Glutathione-Based Antioxidative System

ABSTRACT Laccase is a copper-containing polyphenol oxidase that has great potential in industrial and biotechnological applications. Previous research has suggested that fungal laccase may be involved in the defense against oxidative stress, but there is little direct evidence supporting this hypothesis, and the mechanism by which laccase protects cells from oxidative stress also remains unclear. Here, we report that the expression of the laccase gene from white rot fungus in Pichia pastoris can significantly enhance the resistance of yeast to H2O2-mediated oxidative stress. The expression of laccase in yeast was found to confer a strong ability to scavenge intracellular H2O2 and to protect cells from lipid oxidative damage. The mechanism by which laccase gene expression increases resistance to oxidative stress was then investigated further. We found that laccase gene expression in Pichia pastoris could increase the level of glutathione-based antioxidative activity, including the intracellular glutathione levels and the enzymatic activity of glutathione peroxidase, glutathione reductase, and γ-glutamylcysteine synthetase. The transcription of the laccase gene in Pichia pastoris was found to be enhanced by the oxidative stress caused by exogenous H2O2. The stimulation of laccase gene expression in response to exogenous H2O2 stress further contributed to the transcriptional induction of the genes involved in the glutathione-dependent antioxidative system, including PpYAP1, PpGPX1, PpPMP20, PpGLR1, and PpGSH1. Taken together, these results suggest that the expression of the laccase gene in Pichia pastoris can enhance the resistance of yeast to H2O2-mediated oxidative stress by stimulating the glutathione-based antioxidative system to protect the cell from oxidative damage.

Thermogravimetric study and kinetic analysis of fungal pretreated corn stover using the distributed activation energy model.

Non-isothermal thermogravimetry/derivative thermogravimetry (TG/DTG) measurements are used to determine pyrolytic characteristics and kinetics of lignocellulose. TG/DTG experiments at different heating rates with corn stover pretreated with monocultures of Irpex lacteus CD2 and Auricularia polytricha AP and their cocultures were conducted. Heating rates had little effect on the pyrolysis process, but the peak of weight loss rate in the DTG curves shifted towards higher temperature with heating rate. The maximum weight loss of biopretreated samples was 1.25-fold higher than that of the control at the three heating rates, and the maximum weight loss rate of the co-culture pretreated samples was intermediate between that of the two mono-cultures. The activation energies of the co-culture pretreated samples were 16-72 kJ mol(-1) lower than that of the mono-culture at the conversion rate range from 10% to 60%. This suggests that co-culture pretreatment can decrease activation energy and accelerate pyrolysis reaction thus reducing energy consumption.

The promoting effect of byproducts from Irpex lacteus on subsequent enzymatic hydrolysis of bio-pretreated cornstalks

BackgroundIrpex lacteus, a versatile lignin-degrading fungus with various extracellular enzymes, has been widely used for biological pretreatment. However, most studies have focused on the change of substrate structure after biological pretreatment, and the effect of these changes on the enzymatic hydrolysis, but the effect of byproducts from biological pretreatment process on subsequent enzymatic hydrolysis is not well understood.MethodsWe developed a biological pretreatment process with I. lacteus that can produce stimulatory byproducts that enhance the enzymatic hydrolysis of cornstalks.ResultsThe maximum hydrolysis yield of glucan (82%) was obtained after pretreatment for 28 days. The maximum reducing sugar yield decreased from 313.5 to 200.1 mg/g raw cornstalks after water-soluble byproducts of biological pretreatment were removed from pretreated cornstalks. The effect of byproducts on enzymatic hydrolysis was also investigated. We found that the hydrolysis efficiency of commercial cellulase preparation on cornstalks could be improved by water extracts from bio-pretreated cornstalks with hydrolytic enzyme activity and iron-reducing activity.ConclusionThe key finding suggested that byproducts from biological pretreatment play important roles in enhancing downstream hydrolysis, which might be attributable to hydrolytic enzymes and iron-reducing compounds produced by I. lacteus.

The delignification effects of white-rot fungal pretreatment on thermal characteristics of moso bamboo

Moso bamboo (Phyllostachys pubesescens) is a major bamboo species which is widely used for temporary scaffolding in China. Its fast growing and low ash content make moso bamboo a potential renewable energy resource. In present work, thermal behaviors of moso bamboo and its lignocellulosic fractions were investigated using thermogravimetric analysis. Furthermore, to understand whether the delignification effect of white-rot fungi can promote the thermal decomposition of bamboo especially the lignin component, the changes in lignocellulose components as well as thermal behaviors of bamboo and acid detergent lignin were investigated. The results showed that the white-rot fungal pretreatment is advantageous to thermal decomposition of lignin in bamboo. The weight losses of ADL samples became greater and the thermal processes were accelerated after biopretreatment. The total pyrolysis weight loss increased from 57.14% to 65.07% for Echinodontium taxodii 2538 treated bamboo ADL sample.