Twin-screw extrusion of ‘Pesta’-encapsulated biocontrol agents

World Journal of Microbiology and Biotechnology -     

Optimization of L-malic acid production by Aspergillus flavus in a stirred fermentor

Effects of various nutritional and environmental factors on the accumulation of organic acids (mainly L-malic acid) by the filamentous fungus Aspergillus flavus were studied in a 16-L stirred fermentor. Improvement of the molar yield (moles acid produced per moles glucose consumed) of L-malic acid was obtained mainly by increasing the agitation rate (to 350 rpm) and the Fe(z+) ion concentration (to 12 mg/L) and by lowering the nitrogen (to 271 mg/L) and phosphate concentrations (to 1.5 mM) in the medium. These changes resulted in molar yields for L-malic acid and total C(4) acids (L-malic, succinic, and fumaric acids) of 128 and 155%, respectively. The high molar yields obtained (above 100%) are additional evidence for the operation of part of the reductive branch of the tricarboxylic acid cycle in L-malic acid accumulation by A. flavus. The fermentation conditions developed using the above mentioned factors and 9% CaCO(3) in the medium resulted in a high concentration (113 g/L L-malic acid from 120 g/L glucose utilized) and a high overall productivity (0.59 g/L h) of L-malic acid. These changes in acid accumulation coincide with increases in the activities of NAD(+)-malate dehydrogenase, fumarase, and citrate synthase.     

The tetrameric pheromone module SteC‐MkkB‐MpkB‐SteD regulates asexual sporulation,sclerotia formation and aflatoxin production in Aspergillus flavus

For eukaryotes like fungi to regulate biological responses to environmental stimuli, various signalling cascades are utilized, like the highly conserved mitogen‐activated protein kinase (MAPK) pathways. In the model fungus Aspergillus nidulans, a MAPK pathway known as the pheromone module regulates development and the production of secondary metabolites (SMs). This pathway consists five proteins, the three kinases SteC, MkkB and MpkB, the adaptor SteD and the scaffold HamE. In this study, homologs of these five pheromone module proteins have been identified in the plant and human pathogenic fungus Aspergillus flavus. We have shown that a tetrameric complex consisting of the three kinases and the SteD adaptor is assembled in this species. It was observed that this complex assembles in the cytoplasm and that MpkB translocates into the nucleus. Deletion of steC, mkkB, mpkB or steD results in abolishment of both asexual sporulation and sclerotia production. This complex is required for the positive regulation of aflatoxin production and negative regulation of various SMs, including leporin B and cyclopiazonic acid (CPA), likely via MpkB interactions in the nucleus. These data highlight the conservation of the pheromone module in Aspergillus species, signifying the importance of this pathway in regulating fungal development and secondary metabolism.     

Purification and characterization of a novel β-glucosidase from Aspergillus flavus and its application in saccharification of soybean meal

Abstract

Aspergillus flavus has been regarded as a potential candidate for its production of industrial enzymes, but the details of β-glucosidase from this strain is very limited. In herein, we first reported a novel β-glucosidase (AfBglA) with the molecular mass of 94.2?kDa from A. flavus. AfBglA was optimally active at pH 4.5 and 60?°C and is stable between pH 3.5 and 9.0 and at a temperature of up to 55?°C for 30?min remaining more than 90% of its initial activity. It showed an excellent tolerance to Trypsin, Pepsin, Compound Protease, and Flavourzyme and its activity was not inhibited by specific certain cations. AfBglA displayed broad substrate specificity, it acted on all tested pNP-glycosides and barley glucan, indicating this novel β-glucosidase exhibited a β-1, 3-1, 4-glucanase activity. Moreover, the AfBglA could effectively hydrolyze the soybean meal suspension into glucose and exhibit a strong tolerance to the inhibition of glucose at a concentration of 20.0?g/L during the saccharification. The maximum amount of the glucose obtained by AfBglA corresponded to 67.0?g/kg soybean meal. All of these properties mentioned above indicated that the AfBglA possibly attractive for food and feed industry and saccharification of cellulolytic materials.     

A two‐dimensional proteome map of the aflatoxigenic fungus Aspergillus flavus

The filamentous fungus Aspergillus flavus is an opportunistic soil‐borne pathogen that produces aflatoxins, the most potent naturally occurring carcinogenic compounds known. This work represents the first gel‐based profiling analysis of A. flavus proteome and establishes a 2D proteome map. Using 2DE and MALDI‐TOF‐MS/MS, we identified 538 mycelial proteins of the aflatoxigenic strain NRRL 3357, the majority of which were functionally annotated as related to various cellular metabolic and biosynthetic processes. Additionally, a few enzymes from the aflatoxin synthesis pathway were also identified.     

Effect of opportunistic fungi on the life cycle of the root-knot nematode ( Meloidogyne javanica) on brinjal

The effect of four opportunistic fungi viz., Paecilomyces lilacinus, Cladosporium oxysporum, Gliocladium virens and Talaromyces flavus on the life cycle of the root-knot nematode, Meloidogyne javanica, on brinjal was evaluated under glasshouse conditions. The results revealed that these fungi affected the penetration and development of M. javanica. The life cycle of M. javanica was delayed by 10, 7, 4 and 2 days in the presence of P. lilacinus, C. oxysporum, G. virens and T. flavus respectively. Fecundity, number of eggs per eggmass and number of larvae was also reduced in the presence of these opportunistic fungi. However, the number of males increased in the presence of opportunistic fungi.     

RAPD analysis of genetic diversity among the isolates of Aspergillus flavus from different hosts and locations

Aflatoxin contamination is a major problem in maize, groundnut, chillies, cotton and tree nuts. These aflatoxins are low molecular weight toxic and carcinogenic secondary metabolites produced by Aspergillus flavus, A. parasiticus and A. nomius. In the present study, a total of 11 isolates of A. flavus isolated from groundnut, maize and chilli collected from different locations of Tamil Nadu, India were tested for their ability to produce aflatoxin B1 (AFB1) in vitro by indirect competitive enzyme-linked immunosorbent assay. The results show that the isolates vary in their level of toxin production. The amount of AFB1 produced by the toxigenic isolates of A. flavus ranged from 6.6 to 108.1?ng?ml^?1. Among the various isolates of A. flavus, the isolate VKR produced the highest amount (108.1?ng?ml^?1) of AFB1. The isolates viz. CBE1, CBE2, BSR1, BSR3 and BSR4 were found to be non-toxigenic. The genetic variability among these isolates was assessed by Random amplified polymorphic DNA (RAPD) analysis. DNA fragments of between 0.15 and 3.0?kb were obtained using 13 random primers, and each isolate differed in the size and number of PCR products indicating considerable polymorphism. Cluster analysis using Unweighted Pair Group Method with Arithmetic Mean clearly separated the isolates into four main clusters confirming the genetic diversity among the isolates of A. flavus. Both toxigenic and non-toxigenic isolates were intermingled in these four groups, indicating that no relationship exists between RAPD profile and the production of aflatoxin by A. flavus.     

我国首例肌曲霉病及其试验研究

目的报道国内首例肌曲霉病,对所分离的黄曲霉进行形态、药敏、rDNA序列分析研究。方法对患者病变肌组织行B超和病理检查;将分离菌株接种于察氏培养基观察形态学特征;微量法测定MIC值;酚氯仿法提取DNA,扩增ITS间区序列并进行多序列分析。结果B超示左腓肠肌不规则回声,病理示肌细胞变性、坏死,肌组织内见分枝分隔菌丝。表型及基因型特征为黄曲霉;分离菌株对多种抗真菌药物耐药;多基因序列分析显示所分离菌株与标准株及自然和临床分离株具有100%的相似性。给予特比萘芬治疗3个月后痊愈。结论黄曲霉可致肌肉感染;药敏试验对临床治疗具有指导意义;环境中普遍存在的真菌可引起免疫低下患者致死性感染。     

Analysis of single nucleotide polymorphisms in three genes shows evidence for genetic isolation of certain Aspergillus flavus vegetative compatibility groups

Genetic exchange by asexual filamentous fungi is presumed to be limited to isolates in the same vegetative compatibility group (VCG). To evaluate genetic isolation of Aspergillus flavus due to vegetative incompatibility, three gene regions were chosen that contained closely spaced nucleotides that were polymorphic among some of the six VCGs examined. A member of each VCG was collected from five regions across the southern United States. Isolates belonging to the same VCG had similar sets of single nucleotide polymorphisms regardless of isolate origin. The six VCGs formed four genetically distinct groups. Although recombination between certain pairs of VCGs could not be excluded, none was found for YV36, the VCG that includes the atoxigenic A. flavus isolate currently used to mitigate aflatoxin contamination in cotton in Arizona.