Isolation of mutants of Aspergillus awamori with enhanced production of extracellular xylanase and ?-xylosidase

Upstream and downstream processing of lovastatin by Aspergillus terreus

The present study describes the enhanced production and purification of lovastatin by Aspergillus terreus in submerged batch fermentation. The enhancement of lovastatin production from A. terreus was attempted by random mutagenesis using ultraviolet radiations and nitrous acid. UV mutants exhibited increased efficiency for lovastatin production as compared with nitrous acid mutants. Among all the mutants developed, A. terreus UV-4 was found to be the hyper producer of lovastatin. This mutant gave 3.5-fold higher lovastatin production than the wild culture of A. terreus NRRL 265. Various cultural conditions were also optimized for hyper-producing mutant strain. 5 % glucose as carbon source, 1.5 % corn steep liquor as nitrogen source, initial pH value of 6, 120 h of incubation period, and 28 °C of incubation temperature were found as best parameters for higher lovastatin production in shake flasks. Production of lovastatin by wild and mutant strains of A. terreus was also scaled up to laboratory scale fermentor. The fermentation process was conducted at 28 °C, 200 rpm agitation, and 1vvm air flow rate without pH control. After the optimization of cultural conditions in 250 ml Erlenmeyer flasks and scaling up to laboratory scale fermentor, the mutant A. terreus UV-4 gave eightfold higher lovastatin production (3249.95 μg/ml) than its production by wild strain in shake flasks. Purification of lovastatin was carried out by solvent extraction method which yielded 977.1 mg/l of lovastatin with 98.99 % chromatographic purity and 26.76 % recovery. The crystal structure of lovastatin was determined using X-ray diffraction analysis which is first ever reported.

Gamma radiation induced mutagenesis in Aspergillus niger to enhance its microbial fermentation activity for industrial enzyme production

α- and β-Galactosidases find application in food processing, health and nutrition. Aspergillus niger is one of the potent producer of these enzymes and was genotypically improved using gamma-ray induced mutagenesis. The mutant-derivative produced two-fold higher α- and β-galactosidases. For testing genetic variability and its relationship with phenotypic properties of the two organisms, DNA samples of the mutant and parental strains of A. niger were amplified with 28 deca-nucleotide synthetic primers. RAPD analysis showed significantly different pattern between parental and mutant cultures. The mutant derivative yielded homogeneous while parental strain formed heterogeneous amplification patterns. Seven primers identified 42.9% polymorphism in the amplification products, indicating that these primers determined some genetic variability between the two strains. Thus RAPD was found to be an efficient technique to determine genetic variability in the mutant and wild organisms. Both wild and mutant strains were analyzed for their potential to produce galactosidases. Comparison of different carbon sources on enzyme yield revealed that wheat bran is significant (P < 0.01) effective producer and economical source followed by rice bran, rice polishing and lactose. The mutant was significantly better enzyme producer and could be considered for its prospective application in food, nutrition and health and that RAPD can be effectively used to differentiate mutant strain from the parental strain based on the RAPD patterns.

D-xylan-degrading enzyme system from the fungus Phanerochaete chrysosporium: isolation and partial characterisation of an alpha-(4-O-methyl)-D-glucuronidase

A number of fungi were screened for their capacities to produce extracellular alpha-(4-O-methyl)-D-glucuronidase. Of those tested, Phanerochaete chrysosporium ATCC 24725 produced the enzyme in greatest yield. The single alpha-(4-O-methyl)-D-glucuronidase produced by this fungus was purified by a series of chromatographic methods involving anion exchange, hydrophobic interaction and chromatofocusing. Isolated in this way, the enzyme had an apparent molecular mass of 112 kDa in sodium dodecyl sulphate polyacrylamide gels, and a pI of 4.6 when determined by isoelectric focusing in polyacrylamide gels. The enzyme was optimally active at pH 3.5, but showed significant activity over the pH range 3-5. In the absence of substrate the enzyme was inactivated at pH 3.5 in 2 h at 50 degree C: at pH 5.0 it retained 42% of its activity for 24 h at this temperature. The enzyme showed little activity on glucuronoxylan polysaccharides, but some short-chain xylo-oligosaccharides which were substituted with alpha-linked 4-O-methyl-D-glucopyranosyl uronic acid attached to the 2-position of the non-reducing D-xylopyranosyl residue were readily hydrolysed. There were marked synergistic effects apparent in the release of 4-O-methyl-D-glucopyranosyl uronic acid from various glucuronoxylans when the alpha-(4-O-methyl)-D-glucuronidase was acting in concert with endo-(1-->4)-beta-D-xylanase, and with beta-D-xylosidase and/or an alpha-L-arabinofuranosidase.