Purification of the alkaliphilic xylanases from Myceliophthora sp. IMI 387099 using cellulose-binding domain as an affinity tag

Fibre digestion by rumen microbiota — a review of recent metagenomic and metatranscriptomic studies

Plant biomass is the most abundant renewable resource on the planet, and the biopolymers of lignocellulose are the foundation of ruminant production systems. Optimizing the saccharification of lignocellulosic feeds is a crucial step in their bioconversion to ruminant protein. Plant cell walls are chemically heterogeneous structures that have evolved to provide structural support and protection to the plant. Ruminants are the most efficient digesters of lignocellulose due to a rich array of bacteria, archaea, fungi, and protozoa within the rumen and lower digestive tract. Metagenomic and metatranscriptomic studies have enhanced the current understanding of the composition, diversity, and function of the rumen microbiome. There is particular interest in identifying the carbohydrate-active enzymes responsible for the ruminal degradation of plant biomass. Understanding the roles of cellulosomes- and polysaccharide-utilising loci in ruminal fibre degradation could provide insight into strategies to enhance forage utilisation by ruminants. Despite advancements in “omics” technology, the majority of rumen microorganisms are still uncharacterised, and their ability to act synergistically is still not understood. By advancing our current knowledge of rumen fibre digestion, there may be opportunity to further improve the productive performance of ruminants fed forage diets.

Saccharification efficiencies of multi-enzyme complexes produced by aerobic fungi

In the present study, we have characterized high molecular weight multi-enzyme complexes in two commercial enzymes produced by Trichoderma reesei (Spezyme CP) and Penicillium funiculosum (Accellerase XC). We successfully identified 146-1000 kDa complexes using Blue native polyacrylamide gel electrophoresis (BN-PAGE) to fractionate the protein profile in both preparations. Identified complexes dissociated into lower molecular weight constituents when loaded on SDS PAGE. Unfolding of the secondary structure of multi-enzyme complexes with trimethylamine (pH >10) suggested that they were not a result of unspecific protein aggregation. Cellulase (CMCase) profiles of extracts of BN-PAGE fractionated protein bands confirmed cellulase activity within the multi-enzyme complexes. A microassay was used to identify protein bands that promoted high levels of glucose release from barley straw. Those with high saccharification yield were subjected to LC-MS analysis to identify the principal enzymatic activities responsible. The results suggest that secretion of proteins by aerobic fungi leads to the formation of high molecular weight multi-enzyme complexes that display activity against carboxymethyl cellulose and barley straw.

Thermodynamics and kinetic properties of halostable endoglucanase from Aspergillus fumigatus ABK9

An endoglucanase from Aspergillus fumigatus ABK9 was purified from the culture extract of solid-state fermentation and its some characteristics were evaluated. The molecular weight of the purified enzyme (56.3 kDa) was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, zymogram analysis and confirmed by MALDI-TOF mass spectrometry. The enzyme was active optimally at 50 °C, pH 5.0 and stable over a broad range of pH (4.0-7.0) and NaCl concentration of 0-3.0 M. The pKa1 and pKa2 of the ionizable groups of the active sites were 2.94 and 6.53, respectively. The apparent Km , Vmax , and Kcat values for carboxymethyl cellulose were 6.7 mg ml(-1), 775.4 µmol min(-1) , and 42.84 × 10(4)  s(-1), respectively. Thermostability of the enzyme was evidenced by the high activation energy (91.45 kJ mol(-1)), large enthalpy for activation of denaturation (88.77 kJ mol(-1)), longer half-life (T1/2) (433 min at 50 °C), higher melting temperature (Tm ) (73.5 °C), and Q10 (1.3) values. All the characteristics favors its suitability as halotolerant and thermostable enzyme during bioprocessing of lignocellulosic materials.

Studies on an alkali-thermostable xylanase from Aspergillus fumigatus MA28

An alkalitolerant fungus, Aspergillus fumigatus strain MA28 produced significant amounts of cellulase-free xylanase when grown on a variety of agro-wastes. Wheat bran as the sole carbon source supported higher xylanase production (8,450 U/L) than xylan (7,500 U/L). Soybean meal was observed to be the best nitrogen source for xylanase production (9,000 U/L). Optimum medium pH for xylanase production was 8 (9,800 U/L), though, significant quantities of the enzyme was also produced at pH 7 (8,500 U/L), 9 (8,200 U/L) and 10 (4,600 U/L). The xylanase was purified by ammonium sulphate precipitation and carboxymethyl cellulose chromatography, and was found to have a molecular weight of 14.4 kDa with a V(max) of 980 μmol/min/mg of protein and a K(m) of approximately 4.9 mg/mL. The optimum temperature and pH for enzyme activity was 50 °C and pH 8, respectively. However, the enzyme also showed substantial residual activity at 60-70 °C (53-75%) and at alkaline pH 8-9 (56-88%).

Purification and characterization of two thermostable xylanases from Malbranchea flava active under alkaline conditions

Two xylanases, MFX I and MFX II, from the thermophilic fungus Malbranchea flava MTCC 4889 with molecular masses of 25.2 and 30kDa and pIs of 4.5 and 3.7, respectively were purified to homogeneity. The xylanases were optimally active at pH 9.0 and at 60 degrees C, exhibited a half-life of 4h at 60 degrees C, and showed distinct mode of action and product profiles when applied to birchwood, oat spelt, and larchwood xylan, and to wheat and rye arabinoxylan. The xylanases were most active on larchwood xylan with K(m) values of 1.25 and 3.7mg/ml. K(cat)/K(m) values suggested that the xylanases preferentially hydrolyzed rye arabinoxylan. LC-MS/MS (liquid chromatography/mass spectrometry) analysis of tryptic digests of MFX I and MFX II revealed similarity with known fungal xylanases and suggests that that they belonged to the GH 11 and 10 glycosyl hydrolase super families, respectively. These xylanases can potentially be used in enzyme-assisted bleaching of the pulp derived from agro-residues, as well as production of xylooligosaccharides for pre-biotic functional food applications.