Fungal cellulase; production and applications: minireview

Cellulose is the most abundant biomaterial derived from the living organisms on the earth; plant is the major contributor to the cellulose pool present in the biosphere. Cellulose is used in variety of applications ranging from nanomaterials to biofuel production. For biofuel production, cellulose has first to be broken-down into its building blocks; β-D-glucosyl unit which subsequently can be fermented to different product such as ethanol, acetic acids, among others. Cellulase is the enzymatic system, which degrades cellulose chains to glucose monomers. Cellulase is a group of three enzymes endoglucanase, exoglucanases and β-glucosidases which act together to hydrolyze cellulose to glucose units. Cellulases are found in bacteria, fungi, plants, and some animals. Fungi are the preferred source of cellulase for industrial applications since they secrete large quantities of cellulase to culture medium. Despite a remarkable number of fungi found to produce cellulase enzymes, few have been extensively investigated because they produce large quantities of these enzymes extracellularly. In this mini-review, the production of cellulase from fungi and the parameters affecting cellulase production are discussed briefly on light of recent publications. Furthermore, potential applications of cellulase enzymes are highlighted

Analysis of a conserved cellulase transcriptional regulator reveals inducer-independent production of cellulolytic enzymes in Neurospora crassa.

Cellulose is recalcitrant to deconstruction to glucose for use in fermentation strategies for biofuels and chemicals derived from lignocellulose. In Neurospora crassa, the transcriptional regulator, CLR-2, is required for cellulolytic gene expression and cellulose deconstruction. To assess conservation and divergence of cellulase gene regulation between fungi from different ecological niches, we compared clr-2 function with its ortholog (clrB) in the distantly related species, Aspergillus nidulans. Transcriptional profiles induced by exposure to crystalline cellulose were similar in both species. Approximately 50% of the cellulose-responsive genes showed strict dependence on functional clr-2/clrB, with a subset of 28 genes encoding plant biomass degrading enzymes that were conserved between N. crassa and A. nidulans. Importantly, misexpression of clr-2 under noninducing conditions was sufficient to drive cellulase gene expression, secretion, and activity in N. crassa, to a level comparable to wild type exposed to Avicel. However, misexpression of clrB in A. nidulans was not sufficient to drive cellulase gene expression under noninducing conditions, although an increase in cellulase activity was observed under crystalline cellulose conditions. Manipulation of clr-2 orthologs among filamentous fungi may enable regulated cellulosic enzyme production in a wide array of culture conditions and host strains, potentially reducing costs associated with enzyme production for plant cell wall deconstruction. However, this functionality may require additional engineering in some species

Cellulase Production by Wild-type Aspergillus niger, Penicillium chrysogenum and Trichoderma harzianum Using Waste Cellulosic Materials

Waste cellulosic materials (corncob, sawdust and sugarcane pulp) and crystalline cellulose induced cellulase production in wild strains of Aspergillus niger, Penicillium chrysogenum and Trichoderma harzianum isolated from a wood-waste dump in Lagos, Nigeria. Cellulose-supplemented media gave the maximum cellulase activity of 0.54, 0.67 and 0.39 units mg Protein-1 for A. niger, P. chrysogenum and T. harzianum respectively. The maximum enzyme activity for A. niger was obtained at 36 h of cultivation, while P. chrysogenum and T. harzianum gave their maximum enzyme activities at 12 and 60 h respectively. For the cellulosic wastes, highest enzyme activity was obtained with sawdust where A. niger, P. chrysogenum and T. harzianum gave the maximum enzyme activity of 0.30, 0.24 and 0.20 units mg Protein-1 respectively after 144 h of cultivation. A. niger recorded the highest enzyme activity with any of the three cellulosic materials followed by P. chrysogenum. It thus appears that the use of sawdust presents the best option for low-cost commercial production of cellulase using A. niger and P. chrysogenum as discussed herewith

GROWTH AND CELLULASE ACTIVITY OF WILD-TYPE ASPERGILLUS NIGER ANL301 IN DIFFERENT CARBON SOURCES

A wild-type Aspergillus niger (ANL301) isolated from wood-waste in Lagos, Nigeria, produces extracellular proteins with cellulase (EC 3. 2. 1. 4) activity. Three different carbon sources (Glucose, Cellulose and Sawdust) influenced the organism’s growth and the production of extracellular cellulase enzymes. Best growth was obtained with glucose at 72 hours of incubation. The peak mycelia weight of 1.56 mg/ mL obtained with glucose was about 3 times the maximum weight of 0.58 and 0.49 mg/ mL respectively obtained with cellulose and sawdust at 96 hours. The peak protein contents of the culture filtrates were 0.02, 0.15 and 0.69 mg/ mL respectively in the media containing glucose, cellulose and sawdust. There was no significant cellulase activity in the filtrates from glucose-containing media. The culture filtrates of the organism from cellulose- and sawdust-containing media yielded significant cellulase activities with maximum values of 105.6 Units /L (at 72 hours for cellulose) and 101.9 Units /L (at 144 hours for sawdust). There is a correlation between the protein content and cellulase activity of the culture filtrates. Sawdust can serve as a low-cost substrate for cellulase production by the organism

Optimization of Cellulase Production by Chaetomium Globosum Strain 414 Using Oil Palm Empty Fruit Bunch Fibre as Substrate

The production of three major components of cellulase (FPase, CMCase and 13-glucosidase) by Chaetomium globoslim strain 414 was studied in a shake flask experiment. The effects of physical and chemical treatments on the oil palm empty fruit bunch (OPEFB) fibre for subsequent use as substrate for cellulase production were investigated. The effects of different types and concentrations of nitrogen sources on cellulase production were also examined. The optimized medium composition obtained from the shake flask experiment was used for cellulase production in a 2L stirred tank ferrnenter (impeller tip speed = 1.64 mls) where the effect of different levels of dissolved oxygen tension (DOT) at a fixed agitation speed on cellulase production was investigated. The experimental data obtained from batch fermentations in a shake flask and the fermenter using the optimized medium were analysed to form the basis for a kinetic model ofthe process. The partially purified cellulase preparation from this fungus was used for the saccharification of OPEFB fibre. The effect of different methods of treatment of OPEFB fibre on the rate and degree of hydrolysis was investigated.The use of2-mm OPEFB fibre increased cellulase production about two fold compared to 10-mm fibre. Chemical treatment significantly increased the cellulose and reduced the lignin contents. Cellulase activities, obtained from fermentation using OPEFB fibre treated with 0.5% RN03 followed by autoclaving were about three times higher than those obtained in fermentation using pure celluloses. The cellulase of C. globosum strain 414 contained a high proportion of l3-glucosidase with the ratio of specific activity of l3-glucosidase to FPase of about 8. Peptone gave the highest cellulase production followed by yeast extract, urea, KN03 and (NH4)2S04' A good agreement between the calculated data and the experimental data for both cell growth and cellulase production were observed, suggesting that the proposed model based on logistic and Luedeking-Piret equations is sufficient to describe the growth of C. globosum strain 414 and cellulase production. The maximum activities of FPase, CMCase and l3-glucosidase obtained from fermentation with 50% DOT were 2.5, 59.5 and 12.8 U/m), and these gave the overall productivities of20.8, 495 and 53.3 U/L.h, respectively. Cellulase production in stirred tank fermenter were significantly higher than that obtained in shake flask. The yield and overall productivity of the saccharification of the autoclaved OPEFB fibre treated with 2% NaOH were 0.7600 g reducing sugar/g OPEFB and 0.0178 g reducing sugar/g cellulose.h, respectively

Liquid state bioconversion of palm oil mill effluent for cellulase production: statistical optimization of process conditions

The filamentous fungus Trichoderma harzianum was used for liquid state bioconversion of POME for cellulase production. Statistical optimization was carried out to evaluate the physico-chemical parameters (factors) for maximum cellulase production by 2-level fractional factorial design with six central points. The polynomial regression model was developed using the experimental data including the effects of linear, quadratic and interaction of the factors. The factors involved were substrate (POME) and co-substrate (wheat flour) concentrations, temperature, pH, inoculum and agitation. Statistical analysis showed that the optimum conditions were: temperature of 300C, substrate concentration of 2%, wheat flour concentration of 3%, pH of 4, inoculum of 3% and agitation of 200 rpm. Under these conditions, the model predicted the enzyme production to be about 14 FPU/ml. Analysis of variance (ANOVA) of the design showed a high coefficient of determination (R2) value of 0.99, thus ensuring a high satisfactory adjustment of the quadratic model with the experimental data

A novel enzymatic approach to nanocrystalline cellulose preparation

In this work, conditions for an enzymatic pretreatment prior to NCC isolation from cotton linter were assessed. Different cellulase doses and reaction times were studied within an experimental design and NCC were obtained. At optimal enzymatic conditions (20U, 2 h), a total yield greater than 80% was achieved and the necessary enzymatic treatment time was reduced 90%. Different intensities of enzymatic treatments led to proportional decreases in fiber length and viscosity and also were inversely proportional to the amount of released oligosaccharides. These differences within fibers lead to quantitative differences in NCC: increase in acid hydrolysis yield, reduction of NCC surface charge and crystallinity increase. Benefits produced by enzymatic treatments did not have influence over other NCC characteristics such as their sulfur content (˜1%), size (˜200 nm), zeta potential (˜-50 mV) or degree of polymerization (˜200). Evidence presented in this work would reduce the use of harsh sulfuric acid generating a cleaner stream of profitable oligosaccharidesPostprint (author's final draft