Applications of Hydrolytic and Decarboxylating Enzymes in Biotransformations

Peptides, and oligosaccharides and glycosides, can be synthesised by making use of the ‘reverse hydrolytic activity’ of proteases and glycosidases respectively. In applying these enzymes to the practical synthesis of these classes of compound, several factors need to be considered, namely the need to shift the rate-determining step through the use of activated substrates, the need to minimise competing hydrolysis of these and the need to minimise hydrolysis of the products. In spite of these problems, the enzymatic methods have many attractive features, not least amongst which is the absolute control of stereochemistry in acyl transfer and glycosyl transfer respectively.     

Comparison of Groupings among Members of the Genus Aspergillus Based on Phylogeny and Production of Bioactive Compounds

Three hundred sixty-six Aspergillus strains preserved at the National Institute of Technology and Evaluation (NITE) were compared as to phylogenetic relationships (11 species-clusters) based on the DNA sequences of the D1/D2 domains of LSU rRNA and ITS regions, including the 5.8S rRNA and biological activities of their secondary metabolites. The results showed relatively well correlation between the phylogenetic distribution and the production of bioactive compounds, especially, antimicrobial activities.     

Biosynthesis of glyantrypine by Aspergillus clavatus

The biosynthesis of glyantrypine from radiolabelled amino acid precursors has been shown experimentally to involve anthranilic acid, tryptophan and glycine. Low values for percentage incorporation of radiolabel into glyantrypine were partly influenced by a complex array of other novel alkaloids shown by the radiolabelling experiments to be related to glyantrypine. Interpretation of radiolabel incorporation from [14C-carboxyl]-anthranilic acid into microbial metabolites seen to contain an anthranilyl moiety in various biosynthetic arrangements is discussed. The possibility of diversion of anthranilic acid from the kynurenine pathway to glyantrypine biosynthesis is recognised.     

Aspergillus myositis in a patient with a myelodysplastic syndrome

We present the case of an elderly man who, while being treated with corticosteroids for a myelodysplastic syndrome, developed myositis of the calf due to Aspergillus fumigatus. Despite therapy with amphotericin B the myositis failed to resolve and he died. At autopsy, a localized necrotizing myositis of the right calf was found with no evidence of disseminated Aspergillus infection. Myositis in the setting of disseminated candidiasis or cryptococcosis has been previously reported. This case is unique in that it is the first reported case of localized fungal myositis and of myositis caused by Aspergillus.     

Effect on aflatoxin production of competition between wild-type and mutant strains of Aspergillus parasiticus

Co-cultivation of a strain of Aspergillus parasiticus, capable of making aflatoxins, with blocked mutant strains, capable of producing none or only a low level of aflatoxins, reduced the net yield of aflatoxins more than that expected based on spore recovery. Yields of aflatoxins were 8-fold less for a norsolorinic acid-producing strain, 14-fold less for an averantin-producing strain, 6-fold less for an averufin-producing strain, and 21-fold less for a versicolorin A-producing strain when co-cultured in equal amounts with a wild-type strain of Aspergillus parasiticus. Even when the wild-type strain was initially present in 100-fold excess, with two of the mutant strains, reduced aflatoxin production was still observed.     

Production of sterigmatocystin by Aspergillus versicolor isolated from roughage

A total of 69 samples of hay and straw collected during the winter period of 1984/85 were surveyed for their contamination by Aspergillus versicolor. The percentage of A. versicolor-positive samples was 14.5%. Nineteen A. versicolor strains mainly isolated from roughage were tested for the production of sterigmatocystin. All of the isolates examined were capable of producing different levels of sterigmatocystin on a cracked corn substrate. The majority of these strains were highly toxigenic; 53% of the isolates produced more than 500 mg/kg of sterigmatocystin. These findings suggest that corn is a very suitable substrate for sterigmatocystin production and that particularly in the surface layers of feed stocks and corn silos such toxigenic strains of A. versicolor can produce considerable growth and possibly sterigmatocystin, too.     

Correlation between manganese-deficiency,loss of respiratory chain complex I activity and citric acid production in Aspergillus niger

The correlation between manganese deficiency, loss of mitochondrial respiratory chain NADH: ubiquinone oxidoreductase (complex I) activity and citric acid overproduction in the Aspergillus niger strain B 60 was analysed. With increasing manganese-supplementation of the production medium the loss of complex I activity and the production of citric acid was reduced. Addition of manganese during growth stopped further loss of complex I activity and further increase of citric acid production. A possible causality between complex I deficiency and citric acid overproduction is discussed.     

Biotransformation of germacrane-type sesquiterpenoids by Aspergillus niger

Three germacrane-type sesquiterpenoids, (+)-germacrone-4,5-epoxide, germacrone and (+)-curdione were biotransformed by Aspergillus niger to give hydroxylated guaiane-type sesquiterpenoids together with allylic alcohols and spirolactone.     

Preharvest seed infection byAspergillus flavus group fungi and subsequent aflatoxin contamination in groundnuts in relation to soil types

Preharvest seed infection byAspergillus flavus and aflatoxin contamination in selected groundnut genotypes (fourA. flavus-resistant and fourA. flavus-susceptible) were examined in different soil types at several locations in India in 1985–1990. Undamaged mature pods were sampled at harvest and seed examined forA. flavus infection and aflatoxin content in two or more trials at ICRISAT Center on light sandy soils and red sandy loam soils (Alfisols), and on Vertisols, at Anantapur on light sandy soils, and at Dharwad and Parbhani on Vertisols. Rainy season trials (1985–1989) were all rainfed. Post-rainy season trials were irrigated; late-season drought stress (90 days after sowing (DAS) until harvest at 125 DAS) was imposed in the 1987/88 and 1989/90 seasons.A. flavus infection and aflatoxin contamination levels were much lower in seed of all genotypes from Vertisols than in seed from Alfisols across locations and seasons. Vertisols also had significantly lower populations ofA. flavus than Alfisols. There were no marked differences between light sandy soils and red sandy loam soils (Alfisols) in respect of seed infection byA. flavus and aflatoxin contamination. Significant interactions between genotypes and soil types were evident, especially in theA. flavus-susceptible genotypes. Irrespective of soil types,A. flavus-resistant genotypes showed lower levels of seed infection byA. flavus and other fungi than didA. flavus-susceptible genotypes. The significance of the low preharvest aflatoxin risk in groundnuts grown on Vertisols is highlighted.ICRISAT Journal Article No. JA 1122