Cellulolytic Cultures Research Articles

An approach to improve methanogenesis through the use of mixed cultures isolated from biogas digester

Biogas production has been shown to be inhibited by branched chain fatty acids (isobutyric, isovaleric) produced in the digester by cellulolytic organisms. Performance of these mixed cellulolytic cultures isolated at 25°C (C25) and at 35° (C35) in a batch digester using cattle manure confirmed that C35, which forms mainly straight chain fatty acids from cellulose was more suitable for use as an inoculum than C25 which formed predominantly branched chain fatty acids. Reconstitution of cellulolytic culture C35 and mixed methanogens M35 almost doubled both the amount and rate of methane production. Cellulolytic culture was useful in pretreatment of water hyacinth prior to its use as a substrate for methane generation A method for preservation and transportation of mixed cellulolytic culture for use as an inoculum in the digester is described.

Purification and properties of two exo-cellobiohydrolases from a cellulolytic culture of Fusarium lini

Two distinct exo-cellobiohydrolases (1,4-β- d-glucan cellobiohydrolase, EC 3.2.1.91) have been isolated from culture filtrates of Fusarium lini by repeated ammonium sulphate fractionation and isoelectric focusing. The purified enzymes were evaluated for physical properties, kinetics and the mechanism of their action. The results of this work were as follows. (1) A two-step enzyme purification procedure was developed, involving isoelectric focusing and ammonium sulphate fractionation. (2) Yields of pure cellobiohydrolases I and II were 45 and 36 mg l −1 of culture broth, respectively. (3) Both enzymes were found to be homogeneous, as determined by ultracentrifugation, isoelectric focusing, electrophoresis in polyacrylamide gels containing SDS and chromatography on Sephadex. (4) The molecular weights of the two cellobiohydrolases, as determined by gel filtration and SDS gel electrophoresis, were 50 000–57 000. (5) Both cellobiohydrolases had low viscosity-reducing and reducing sugar activity from carboxymethyl cellulose and high activity with Walseth cellulose and Avicel. (6) The enzymes produced only cellobiose as the end product from filter paper and Avicel, indicating that they are true cellobiohydrolases. (7) Cellobiohydrolase I hydrolysed d-xylan whereas cellobiohydrolase II was inactive towards d-xylan. (8) There was a striking synergism in filter paper activity when cellobiohydrolase was supplemented with endo-1,4-β- d-glucanase [cellulase, 1,4-(1,3;1,4)-β- d-glucan 4-glucanohydrolase, EC 3.2.1.4] and β- d-glucosidase (β- d-glucoside glucohydrolase, EC 3.2.1.21) .

Rôle of mesophilic fungi in composting

The effect of four mesophilic cellulolytic fungi, Aspergillus niger, Aspergillus sp. (R.), Trichoderma viride and Penicillium sp., on composting of jowar stalk, wheat straw (5:3) and jamun leaves, was investigated. Due to inoculation, the period of composting was reduced by 1 month and the quality of compost improved. Total nitrogen content, available phosphorus and humus content increased in composted material and inoculation with A. niger and Penicillium sp. showed the maximum effect. The possibility of utilising mesophilic, efficient cellulolytic cultures for accelerating the process of composting for efficient recycling of dry, wide C/N ratio materials of a fairly homogeneous nature is indicated.

Single-Cell Protein Production in Alkaline Mesquite Wood Extracts

A nine-member, mixed, cellulolytic, bacterial culture was used to evaluate the effects of sodium hydroxide normality, length and temperature of treatment, and the ratio of volume of alkali to mesquite wood on the suitability of alkali mesquite wood extractives as nutrients for bacterial growth. The presence or absence of air during the extraction process did not significantly affect results. The amount of lignin extracted and the total loss in weight of the wood during extraction were correlated to both alkali concentration and temperature. Neutralized extracts supported bacterial growth; growth was inversely related to the final salt concentration of the neutralized extract. Deionized extracts were superior to acid-neutralized extracts for the support of bacterial growth. The optimum conditions for extraction were 2.5 N NaOH at 30 degrees C for 12 h. The study demonstrated that nutrients as well as growth inhibitory compounds are released from wood by alkali treatment. This study of alkali wood extracts and the previous study of washed alkali treated wood residues provide a data base for the optimization of alkali treatments of hard woods that are to be used as nutrients for the growth of cellulolytic cultures.

Reducing sugar accumulation from alkali pretreated sugar cane bagasse using Cellulomonas

An active cellulolytic culture was obtained following growth of the Cellulomonas strain CS1-17 for 24 h at 32° C on 1 or 2% alkali pretreated sugar cane bagasse. Environmental conditions were then varied to favour reducing sugar accumulation from fresh alkali pretreated bagasse added to the 24 h culture medium at 75 g/l. After incubation for an additional 48 h at 37° C under anaerobic, aerobic and aerobic+0.2% sodium azide conditions, reducing sugar was accumulated at 22.8, 23.7 and 25.6 g/l respectively. Approximately 83% of this release occurred during the first 18 h of incubation and the reducing sugar released contained approximately 14% xylose, 35% glucose, and 26% cellobiose. Addition of exogenous cellobiase resulted in conversion of the cellobiose to glucose.

Isolation of an anaerobic cellulolytic mixed culture

Isolation and enrichment cultures were made for anaerobic cellulose utilizing micro-organisms from non-ruminant sources. Stable mixed cultures were developed which degraded pure cellulose (wet-milled filter paper) in a defined mineral salts medium. Components of the mixed cultures lost viability in monoculture when grown on cellulose. Growth on cellulose was stimulated at low oxygen concentrations, when increased cellulase activity and increased volatile fatty acid production occurred.

Effect of Cellulase on Cotton Fiber Microstructure

Electron microscopical studies of changes in cotton fiber microstructure, after ex posure of the fibers to the cellulase in filtrates prepared from cultures of Myrothecium verrucaria, showed evidence of the transverse, jagged cuts into the cellulose structure previously seen by cytical microscopy. The degradation appeared localized in areas along the length of the fiber which were not related to any recognized component of fiber structure. Micrographs of fragmented, degraded fibers showed etching of the macro- fibrils of the sheets of secondary wall and a sharpening of the image of the individual microfibrils. Continued enzyme attack produced smaller fragments and hydrocellulose- like particles. Measurements of changes in tensile strength, swelling in alkali, and in glucose yield were correlated with changes in microstructure. The extent of fiber degradation by cellulolytic culture filtrates was limited and could be continued only if fibers were swollen between filtrate exposures. No evidence of damage to the cellulose structure was seen which could not be explained hy hydrolysis at the β-1,4-glucosidic linkage.