Abstract:One of the requirements for advancement of nanotechnology are the development of reliable experimental protocols for the synthesis of nanomaterials over a range of biological compositions, sizes and high monodispersity. An attractive possibility of green nanotechnology is to use micro-organisms in the synthesis of nanoparticles. Recently, the utilization of biological systems, especially fungi, has emerged as a novel method for the synthesis of nanoparticles. Nanoparticles are considered as fundamental molecular building blocks for nanotechnology. They are the starting points for preparing many nanostructured materials and devices. In this paper we report the extracellular biosynthesis of silver nanoparticles (AgNPs) by using a fungus named Trichoderma Reesei (also known as Hypocrea jecorina). In the biosynthesis of AgNPs by this fungus, the fungus mycelium is exposed to the silver nitrate solution. That prompts the fungus to produce enzymes and metabolites for its own survival. In this process the toxic Ag+ ions are reduced to the nonetoxic metallic AgNPs through the catalytic effect of the extracellular enzyme and metabolites of the fungus. Absorption UV-Visible light spectroscopy is used to follow up with the reaction process. Fluorescence emission spectroscopy is used to produce detailed information on the progress of reduction of silver nitrate (formation of silver nanoparticles) on the nanosecond timescale. Fourier transform infrared spectroscopy is used for quantitative analyses of the reaction products. Our measurements indicate that extracellular biosynthesis of AgNPs by Trichoderma reesei produces AgNPs with the diameters in the range of 5-50 nm. Trichoderma Reesei is an environmentally friendly fungus, and it is well known for its formation of extracellular enzyme and metabolites in very large amounts, much higher than other fungi. The present process is an excellent candidate for industrial scale production of silver nanoparticles. 66Insciences Journal | Nanotechnology

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Compared with prokaryotes, where horizontal gene transfer events are frequently found and can be studied in the laboratory at the mechanistic level, few systems are known that allow direct experimental access to parasexual phenomena in eukaryotes. In zygomycetes, a basal lineage of fungi, several mycoparasitic fungi are known that inevitably form a cytoplasmic continuum with their hosts during infection. We provide evidence that, corresponding to the expectation suggested by the morphology of the infection process, gene transfer occurs from the parasite to the host. For analysing this parasexual system at the DNA level, we characterized interspecific recombinants obtained by infecting a stable methionine-auxotrophic Absidia glauca mutant with heavy rearrangements at the Met2-1 locus, which encodes homoserine acetyltransferase. Recipients were shown to be complemented by part of the corresponding gene from Parasitella parasitica. This foreign DNA is neither integrated at the putative Met2-2 locus in the recipient strain nor integrated at Met2-1, a locus encoding a hypothetical protein with amino acid similarity but with unknown function. Based on hybridization studies and on the phenotype of recipients that bear some mitotic instability of the acquired prototrophy, we propose that P. parasitica DNA is established in A. glauca recipients as extrachromosomally located replicons.

Transformation of fungi by complementation of auxotrophs is generally much more reliable than usage of antibiotic resistance markers. In order to establish such a system for the model zygomycete Absidia glauca, a stable methionine auxotrophic mutant was isolated after X-ray mutagenesis of the minus mating type and characterized at the molecular level. The mutant is disrupted in the coding region of the Met2-1 gene, encoding homoserine O-acetyltransferase. The corresponding wild type gene was cloned, sequenced and inserted into appropriate vector plasmids. Transformants are prototrophs and show restored methionine-independent growth, based on complementation by the autonomously replicating plasmids.