Stereoselective biotransformations using fungi as biocatalysts
The development of novel biocatalytic methods is a continuously growing area of chemistry, microbiology, and genetic engineering due to the fact that biocatalysts are selective, easy-to-handle, and environmentally friendly. A wide range of reactions are catalyzed by microorganisms. Fungi can be considered as a promising source of new biocatalysts, mainly for chiral reactions. Chemo-, regio-, and stereoselective processes are very important in the synthesis of many chemical, pharmaceutical, and agrochemical intermediates; active pharmaceuticals; and food ingredients. This report reviews stereoselective reactions mediated by fungi, such as stereoselective hydroxylation, sulfoxidation, epoxidation, Baeyer–Villiger oxidation, deracemization, and stereo- and enantioselective reduction of ketones, published between 2000 and 2007. [1]
Toxigenic fungi: which are important?
Growth of commonly occurring filamentous fungi in foods may result in production of mycotoxins, which can cause a variety of ill effects in humans, from allergic responses to immunosuppression and cancer. According to experts, five kinds of mycotoxins are important in human health around the world: aflatoxins, ochratoxin A, fumonisins, certain trichothecenes, and zearalenone. These toxins are produced by only a few species of fungi, in a limited range of commodities. Aflatoxins are potent carcinogens, produced by Aspergillus flavus and A. parasiticus in peanuts, maize and some other nuts and oilseeds. Ochratoxin A is a kidney toxin and probable carcinogen. It is produced by Penicillium verrucosum in cereal grains in cold climates, by A. carbonarius in grapes, wines and vine fruits, and by A. ochraceus sometimes in coffee beans. Fumonisins, which may cause oesophageal cancer, are formed by Fusarium moniliforme and F. proliferatum, but only in maize. Trichothecenes are highly immunosuppressive and zearalenone causes oestrogenic effects; both are produced by F. graminearum and related species. Current reporting probably underestimates the effect of mycotoxins as a cause of human mortality. [2]
Transformation in fungi
Transformation with exogenous deoxyribonucleic acid (DNA) now appears to be possible with all fungal species, or at least all that can be grown in culture. This field of research is at present dominated by Saccharomyces cerevisiae and two filamentous members of the class Ascomycetes, Aspergillus nidulans and Neurospora crassa, with substantial contributions also from fission yeast (Schizosaccharomyces pombe) and another filamentous member of the class Ascomycetes, Podospora anserina. However, transformation has been demonstrated, and will no doubt be extensively used, in representatives of most of the main fungal classes, including Phycomycetes, Basidiomycetes (the order Agaricales and Ustilago species), and a number of the Fungi Imperfecti. The list includes a number of plant pathogens, and transformation is likely to become important in the analysis of the molecular basis of pathogenicity. Transformation may be maintained either by using an autonomously replicating plasmid as a vehicle for the transforming DNA or through integration of the DNA into the chromosomes. In S. cerevisiae and other yeasts, a variety of autonomously replicating plasmids have been used successfully, some of them designed for use as shuttle vectors for Escherichia coli as well as for yeast transformation. Suitable plasmids are not yet available for use in filamentous fungi, in which stable transformation is dependent on chromosomal integration. In Saccharomyces cerevisiae, integration of transforming DNA is virtually always by homology; in filamentous fungi, in contrast, it occurs just as frequently at nonhomologous (ectopic) chromosomal sites. The main importance of transformation in fungi at present is in connection with gene cloning and the analysis of gene function. The most advanced work is being done with S. cerevisiae, in which the virtual restriction of stable DNA integration to homologous chromosome loci enables gene disruption and gene replacement to be carried out with greater precision and efficiency than is possible in other species that show a high proportion of DNA integration events at nonhomologous (ectopic) sites. With a little more trouble, however, the methodology pioneered for S. cerevisiae can be applied to other fungi too. Transformation of fungi with DNA constructs designed for high gene expression and efficient secretion of gene products appears to have great commercial potential. [3]
In vitro Activity of Garlic (Allium sativum) on Some Pathogenic Fungi
Aim: This study was conducted to investigate the in vitro antifungal activity of garlic (Allium sativum) on some pathogenic fungi.
Study Design: This is a comparative evaluation report on garlic as an antifungal agent.
Place and Duration:Department of mycology, Veterinary Research institute, between June-October 2013.
Methodology: Samples of garlic were obtained from a local market. It was thoroughly, cleaned, peeled and pulverized. Aqueous and organic extracts of garlic were obtained by maceration and Soxhlet extractor apparatus. The methanol and petroleum ether extracts were tested against Candida albicans, Aspergillus, Curvularia and some Dermatophyte species using cup diffusion and agar incorporated methods. Diameter of Inhibition zones of growth were measured in millimeter (mm) and expressed as Mean ±SD.
Results: The obtained results revealed that aqueous and petroleum ether extracts possess the stronger activity and a broader fungicidal spectrum against tested fungi compared to methanol extract. The study also showed that the dry coarsely- powdered garlic was found to be more potent to Candida albicans than the commercial Nystatin.
Conclusion: The study demonstrated the potent activity of garlic against tested fungi which encourages its use as a suitable alternative drug for controlling fungal infections because it has far less risk of side-effects than most known antifungal drugs and it can be used indefinitely in quite large amounts. Therefore, adding garlic to food (raw) or crushing and swallowing raw cloves which are cheaper is recommended as a powerful anti-fungal agent. Further purification and formulation of the garlic would give a true antifungal activity comparable to standard antibiotics. [4]
Biodegradation and Detoxification of Bisphenol-A by Filamentous Fungi Screened from Nature
Aims: This study demonstrated obtaining fungal isolates able to degrade and reduce the toxicity of Bisphenol-A (BPA).
Study Design: Soils enclosed by; gas stations, paint industries, and pesticides wastes, Cairo, Egypt, will be used for fungal isolation. BPA will be utilized as a sole carbon and energy source for fungal selectivity. Selected fungal strains will be optimized for BPA degradation. The residues of BPA in cultures will be determined. BPA degradation products will be identified. The toxicity of BPA degradation products on in-vitro cell viability of mammalian cell line will be investigated.
Place and Duration of Study: The study was performed in Mycological lab in botany & microbiology department in faculty of science, Al-azhar university and the Regional Center for Mycology and Biotechnology from October 2012 until May 2014.
Methodology: Different types of media shall be used for isolation, identification and purification processes. Determination of BPA concentrations will be assayed by High performance liquid chromatography (HPLC). BPA degradation products will be identified by Gas chromatography–mass spectrometry (GC-MS). Cytotoxicity test will be measured by Mammalian cell line: Vero cells (derived from the kidney of a normal African green monkey).
Results: Six soil samples were collected from different localities contaminated with petroleum and industrial wastes then 52 fungal isolates were purified before screened for BPA degradation. Two promising fungal isolates Aspergillus terreus (C10) and A. flavus (G1) were selected based on their ability to degrade BPA with percentage 50% and 40% respectively. The effect of different conditions on BPA degradation by (C10) and (G1) including nitrogen sources, incubation temperatures, pH and incubation periods were studied. The highest degradation amount of BPA was obtained from isolates (C10) and (G1) using medium containing sodium nitrate at pH 5 and Yeast extract at pH 7 respectively and incubation temp at 30ºC after incubation at 6 days at shaking state. According to GC-mass the BPA degradation products were identified as following compounds; Thiopropionamide, Methanone, (3-amino-2- benzofuryle) (4- chlorophenyle), 1H-pyrazole, 4,5-dihydro-5,5-dimrthyle-4-isoprpylidene, Phenol, 2,4-isopropylidenedi, Phenol, 2,6-bis(1,1-dimethylethyle)-4- (1-methyle-1-phenylethyle), Bis (2-ethylehexyle) phthalate. The toxicity of BPA was reduced after metabolized by selected fungal strains. Toxicity reduction was measured on cell viability of mammalian cell line.
Conclusion: Our results showed that Aspergillus terreus and A. flavus, have ability to degrade BPA and alter it to less toxic products. These products were tested for their toxicity by cytotoxicity test; the test showed hopeful results while compared it with the toxicity of the original compound. [5]
Reference
[1] Borges, K.B., de Souza Borges, W., Durán-Patrón, R., Pupo, M.T., Bonato, P.S. and Collado, I.G., 2009. Stereoselective biotransformations using fungi as biocatalysts. Tetrahedron: Asymmetry, 20(4), pp.385-397.
[2] Fincham, J.R., 1989. Transformation in fungi. Microbiological reviews, 53(1), pp.148-170.
[3] Fincham, J.R., 1989. Transformation in fungi. Microbiological reviews, 53(1), pp.148-170.
[4] Suleiman, E.A. and Abdallah, W.B., 2014. In vitro activity of garlic (Allium sativum) on some pathogenic fungi. European Journal of Medicinal Plants, pp.1240-1250.
[5] Fouda, A., Khalil, A.M.A., El-Sheikh, H.H., Abdel-Rhaman, E.M. and Hashem, A.H., 2015. Biodegradation and detoxification of bisphenol-A by filamentous fungi screened from nature. Journal of Advances in Biology & Biotechnology, pp.123-132.
