Biological synthesis of silver nanoparticles using the fungus Aspergillus flavus

The fungus, Aspergillus flavus when challenged with silver nitrate solution accumulated silver nanoparticles on the surface of its cell wall in 72 h. These nanoparticles dislodged by ultrasonication showed an absorption peak at 420 nm in UV-visible spectrum corresponding to the plasmon resonance of silver nanoparticles. The transmission electron micrographs of dislodged nanoparticles in aqueous solution showed the production of reasonably monodisperse silver nanoparticles (average particle size: 8.92 ± 1.61 nm) by the fungus. X-ray diffraction spectrum of the nanoparticles confirmed the formation of metallic silver. The Fourier transform infrared spectroscopy confirmed the presence of protein as the stabilizing agent surrounding the silver nanoparticles. These protein-stabilized silver nanoparticles produced a characteristic emission peak at 553 nm when excited at 420 nm in photoluminescence spectrum. The use of fungus for silver nanoparticles synthesis offers the benefits of eco-friendliness and amenability for large-scale production.     

Studies on Mutation Breeding of High-Yielding Xylanase Strains by Low-Energy Ion Beam Implantation

As a new mutagenetic method, low-energy ion implantation has been used widely in many research areas in recent years. In order to obtain some industrial strains with high xylanase yield, the wild type strain Aspergillus niger A3 was mutated by means of nitrogen ions implantation （10 keV, 2.6× 10^14 ～ 1.56 × 10^15 ions/cm^2） and a mutant N212 was isolated subsequently. However, it was found that the initial screening means of the high-yielding xylanase strains such as transparent halos was unfit for first screening. Compared with that of the wild type strain, xylanase production of the mutant N212 was increased from 320 IU/ml to 610 IU/ml, and the optimum fermentation temperature was increased from 28 ℃ to 30 ℃.     

Factors affecting the presence of ochratoxin A in wines

Ochratoxin A (OTA) are synthesized mainly by different species of Aspergillus and Penicillium being its human toxicological effects reflected in different countries due to the consumption of different foods and beverages such as red, white, rose, and special wines. This review presents an overview of the direct (meteorological conditions, grape cultivation, and wine-making techniques) and indirect (latitude, year of production, use of pesticides, presence of spoilage microorganisms, conditions of storage of the harvested grapes, type of maceration, and conditions of fermentation), factors affecting the presence of OTA in wines.     

导致牛肉干产品霉变菌种的分离及鉴定

利用菌种分离鉴定技术,对某工厂留样分析的发霉牛肉干产品进行确认。以菌落生长状况作为综合评价依据,鉴定导致该产品霉变的主要霉菌为帚状曲霉(Aspergillus penicillioides)。该菌嗜高渗透压,只在干燥的基物上生长,在很低的水分活度(0.75)下也能生长,但是在水分活度0.7以下则生长缓慢。对企业生产的指导性建议为：加强工人清洁卫生,内包车间的空气洁净度,同时控制牛肉干产品的水分活度在0.7以下,可以有效防止货架期期间霉变的产生。     

利用透性化黑曲霉细胞制备稀有人参皂苷 Rh1的方法研究

以三七的常量三醇组人参皂苷(含Re、Rg₁、R₁)为底物,研究了不同通透处理工艺对黑曲霉细胞转化人参皂苷Rh₁的影响.实验结果表明:当通透剂为3% EDTA(质量分数),透性化处理时间为30 min(28 ℃),超声处理时间为15 min时,黑曲霉细胞的通透性最佳; 该条件下得到的黑曲霉细胞与三醇组人参皂苷底物反应30 min(45 ℃)时,Rh₁的产量达到最佳.     

Enzyme Processing of Soy Flour with Minimized Protein Loss

The enzymatic treatment of defatted soy flour (SF) to reduce indigestible carbohydrates can result in undesirable protein loss. Here protein loss was minimized with quantitation of the effects of ionic strength (IS), protease activity, and SF toasting. At the enzyme processing condition (25% w/v SF, 50 °C, pH 4.8, 48 hours), protein loss increased linearly with the IS in enzyme broths (EB); e.g., contacting untoasted SF with water or heat-deactivated EB showed protein loss of 28% in water but up to 40% when IS was increased in the range of 0.04–0.19 M. Protein loss also increased with protease in EB (nondeactivated): after adjusted for IS-related loss, approximately 10% and 25% additional protein loss occurred in EB of 73 and 490–557 U/(g SF) protease, respectively. SDS-PAGE results showed that proteolysis was not extensive, mainly on β-conglycinin α'/α and glycinin acidic 37-kDa subunits; and most of the proteolytic products could be recovered by heat-induced precipitation. SF toasting effects were studied, particularly at 2-hours 160°C, with material balances, protein distributions, and monosaccharide yields in hydrolysates. Overall, protein loss was minimized to 5.2% and the conversion of carbohydrate to monomeric sugars increased to 89.2%.     

Rapid Reconstitution of Biosynthetic Machinery for Fungal Metabolites in Aspergillus oryzae: Total Biosynthesis of Aflatrem

Reconstitution of the biosynthetic machinery for fungal secondary metabolites in Aspergillus oryzae provides an opportunity both for stepwise determination of the biosynthetic pathways and the total biosynthesis of fungal natural products. However, to maximize the utility of the reconstitution system, a simple and rapid strategy for the introduction of heterologous genes into A. oryzae is required. In this study, we demonstrated an effective method for introducing multiple genes involved in the biosynthesis of fungal metabolites by using the expression vectors pUARA2 and pUSA2, each of which contains two cloning sites. The successful introduction of all the aflatrem biosynthetic genes (seven genes in total) after two rounds of transformation enabled the total biosynthesis of aflatrem. This rapid reconstitution strategy will facilitate the functional analysis of the biosynthetic machinery of fungal metabolites.     

N-Heterocyclization in Gliotoxin Biosynthesis is Catalyzed by a Distinct Cytochrome P450 Monooxygenase

Gliotoxin and related epidithiodiketopiperazines (ETP) from diverse fungi feature highly functionalized hydroindole scaffolds with an array of medicinally and ecologically relevant activities. Mutation analysis, heterologous reconstitution, and biotransformation experiments revealed that a cytochrome P450 monooxygenase (GliF) from the human-pathogenic fungus Aspergillus fumigatus plays a key role in the formation of the complex heterocycle. In vitro assays using a biosynthetic precursor from a blocked mutant showed that GliF is specific to ETPs and catalyzes an unprecedented heterocyclization reaction that cannot be emulated with current synthetic methods. In silico analyses indicate that this rare biotransformation takes place in related ETP biosynthetic pathways.