Biorefining of wood: combined production of ethanol and xylanase from waste fiber sludge

Metabolic Engineering of Fusarium oxysporum to Improve Its Ethanol-Producing Capability

Fusarium oxysporum is one of the few filamentous fungi capable of fermenting ethanol directly from plant cell wall biomass. It has the enzymatic toolbox necessary to break down biomass to its monosaccharides and, under anaerobic and microaerobic conditions, ferments them to ethanol. Although these traits could enable its use in consolidated processes and thus bypass some of the bottlenecks encountered in ethanol production from lignocellulosic material when Saccharomyces cerevisiae is used—namely its inability to degrade lignocellulose and to consume pentoses—two major disadvantages of F. oxysporum compared to the yeast—its low growth rate and low ethanol productivity—hinder the further development of this process. We had previously identified phosphoglucomutase and transaldolase, two major enzymes of glucose catabolism and the pentose phosphate pathway, as possible bottlenecks in the metabolism of the fungus and we had reported the effect of their constitutive production on the growth characteristics of the fungus. In this study, we investigated the effect of their constitutive production on ethanol productivity under anaerobic conditions. We report an increase in ethanol yield and a concomitant decrease in acetic acid production. Metabolomics analysis revealed that the genetic modifications applied did not simply accelerate the metabolic rate of the microorganism; they also affected the relative concentrations of the various metabolites suggesting an increased channeling toward the chorismate pathway, an activation of the γ-aminobutyric acid shunt, and an excess in NADPH regeneration.

Production of cellulosic ethanol and enzyme from waste fiber sludge using SSF, recycling of hydrolytic enzymes and yeast, and recombinant cellulase-producing Aspergillus niger

Bioethanol and enzymes were produced from fiber sludges through sequential microbial cultivations. After a first simultaneous saccharification and fermentation (SSF) with yeast, the bioethanol concentrations of sulfate and sulfite fiber sludges were 45.6 and 64.7 g/L, respectively. The second SSF, which included fresh fiber sludges and recycled yeast and enzymes from the first SSF, resulted in ethanol concentrations of 38.3 g/L for sulfate fiber sludge and 24.4 g/L for sulfite fiber sludge. Aspergillus niger carrying the endoglucanase-encoding Cel7B gene of Trichoderma reesei was grown in the spent fiber sludge hydrolysates. The cellulase activities obtained with spent hydrolysates of sulfate and sulfite fiber sludges were 2,700 and 2,900 nkat/mL, respectively. The high cellulase activities produced by using stillage and the significant ethanol concentrations produced in the second SSF suggest that onsite enzyme production and recycling of enzyme are realistic concepts that warrant further attention.

Coupled production of single cell oil as biodiesel feedstock, xylitol and xylanase from sugarcane bagasse in a biorefinery concept using fungi from the tropical mangrove wetlands

This work evaluates sugarcane bagasse (SCB) conversion, in a biorefinery approach, to coproduce biodiesel and high value products using two novel mangrove fungi. On acid pre-treatment, sugarcane bagasse hydrolysate (SCBH) resulted in a xylitol yield of 0.51 g/g xylose consumed in 72 h by Williopsis saturnus. After SCB pretreatment, sugarcane bagasse residue (SCBR) was utilized using Aspergillus terreus for production of xylanase (12.74 U/ml) and cell biomass (9.8 g/L) which was extracted for single cell oil (SCO; 0.19 g/g) and transesterified to biodiesel. The FAME profile exhibited long chain SFAs and PUFAs with predicted biodiesel properties lying within the range specified by international standards. This biorefining approach of SCB utilization for co-production of xylitol, xylanase and SCO gains importance in terms of sustainability and eco-friendliness.

Production of bacterial cellulose and enzyme from waste fiber sludge

BACKGROUND

Bacterial cellulose (BC) is a highly crystalline and mechanically stable nanopolymer, which has excellent potential as a material in many novel applications, especially if it can be produced in large amounts from an inexpensive feedstock. Waste fiber sludge, a residue with little or no value, originates from pulp mills and lignocellulosic biorefineries. A high cellulose and low lignin content contributes to making the fiber sludge suitable for bioconversion, even without a thermochemical pretreatment step. In this study, the possibility to combine production of BC and hydrolytic enzymes from fiber sludge was investigated. The BC was characterized using field-emission scanning electron microscopy and X-ray diffraction analysis, and its mechanical properties were investigated.

RESULTS

Bacterial cellulose and enzymes were produced through sequential fermentations with the bacterium Gluconacetobacter xylinus and the filamentous fungus Trichoderma reesei. Fiber sludges from sulfate (SAFS) and sulfite (SIFS) processes were hydrolyzed enzymatically without prior thermochemical pretreatment and the resulting hydrolysates were used for BC production. The highest volumetric yields of BC from SAFS and SIFS were 11 and 10 g/L (DW), respectively. The BC yield on initial sugar in hydrolysate-based medium reached 0.3 g/g after seven days of cultivation. The tensile strength of wet BC from hydrolysate medium was about 0.04 MPa compared to about 0.03 MPa for BC from a glucose-based reference medium, while the crystallinity was slightly lower for BC from hydrolysate cultures. The spent hydrolysates were used for production of cellulase with T. reesei. The cellulase activity (CMCase activity) in spent SAFS and SIFS hydrolysates reached 5.2 U/mL (87 nkat/mL), which was similar to the activity level obtained in a reference medium containing equal amounts of reducing sugar.

CONCLUSIONS

It was shown that waste fiber sludge is a suitable raw material for production of bacterial cellulose and enzymes through sequential fermentation. The concept studied offers efficient utilization of the various components in fiber sludge hydrolysates and affords a possibility to combine production of two high value-added products using residual streams from pulp mills and biorefineries. Cellulase produced in this manner could tentatively be used to hydrolyze fresh fiber sludge to obtain medium suitable for production of BC in the same biorefinery.

An Institutional Approach to Solar Fuels Research

This account gives a brief overview of various directions in current solar fuels research. On that basis, the necessity for an interdisciplinary approach is argued, and an institutional way for promoting this development is presented using the example of the Chemistry Biology Centre (KBC) at Umeå University in Sweden.

Selecting the right blood glucose monitor for the determination of glucose during the enzymatic hydrolysis of corncob pretreated with different methods

In order to assess their accuracy for the determination of glucose during the enzymatic hydrolysis of pretreated lignocellulosic biomass, four different blood glucose monitors (BGMs), each utilizing a different enzymatic mechanism for the determination of glucose, were utilized in an experimental setup, which compares the efficiency of ionic liquid pretreatment with dilute acid and alkaline pretreatments applied on corncob. Among the tested devices, Optium Xceed was found to be the most accurate device for the determination of glucose where Accu-Chek Active was the least accurate BGM, yielding similar results to those obtained with DNS method. Based on the HPLC results, the % error values for Optium Xceed ranged between 3.9-10.5% for the determination of glucose concentration. Upon enzymatic hydrolysis, ionic liquid and alkaline pretreatments gave similar glucose yields, which were slightly higher than the dilute acid pretreatment, which were 31.9%, 31.0% and 27.8%, respectively, based on untreated corncob.