Extracellular Xylanolytic and Pectinolytic Hydrolase Production by Aspergillus flavus Isolates Contributes to Crop Invasion

HacA, a key transcription factor for the unfolded protein response, is required for fungal development, aflatoxin biosynthesis and pathogenicity of Aspergillus flavus

Aspergillus flavus is a fungus notorious for contaminating food and feed with aflatoxins. As a saprophytic fungus, it secretes large amounts of enzymes to access nutrients, making endoplasmic reticulum (ER) homeostasis important for protein folding and secretion. The role of HacA, a key transcription factor in the unfolded protein response pathway, remains poorly understood in A. flavus. In this study, the hacA gene in A. flavus was knockout. Results showed that the absence of hacA led to a decreased pathogenicity of the strain, as it failed to colonize intact maize kernels. This may be due to retarded vegetable growth, especially the abnormal development of swollen tips and shorter hyphal septa. Deletion of hacA also hindered conidiogenesis and sclerotial development. Notably, the mutant strain failed to produce aflatoxin B1. Moreover, compared to the wild type, the mutant strain showed increased sensitivity to ER stress inducer such as Dithiothreitol (DTT), and heat stress. It also displayed heightened sensitivity to other environmental stresses, including cell wall, osmotic, and pH stresses. Further transcriptomic analysis revealed the involvement of the hacA in numerous biological processes, including filamentous growth, asexual reproduction, mycotoxin biosynthetic process, signal transduction, budding cell apical bud growth, invasive filamentous growth, response to stimulus, and so on. Taken together, HacA plays a vital role in fungal development, pathogenicity and aflatoxins biosynthesis. This highlights the potential of targeting hacA as a novel approach for early prevention of A. flavus contamination.

Chromatographic Analysis of Aflatoxigenic Aspergillus flavus Isolated from Malaysian Sweet Corn

High-performance liquid chromatography (HPLC) provides a quick and efficient tool for accurately characterizing aflatoxigenic and non-aflatoxigenic isolates of Aspergillus flavus. This method also provides a quantitative analysis of AFs in Aspergillus flavus. The method’s recovery was assessed by spiking a mixture of AF at different concentrations to the testing medium. The validity of the method was confirmed using aflatoxigenic and non-aflatoxigenic strains of A. flavus. The HPLC system, coupled with a fluorescence detector and post-column photochemical reactor, showed high sensitivity in detecting spiked AFs or AFs produced by A. flavus isolates. Recovery from medium spiked with 10, 20, 60, and 80 ppb of AFs was found to be 73–86% using this approach. For AFB1 and AFB2, the limit of detection was 0.072 and 0.062 ppb, while the limit of quantification was 0.220 and 0.189 ppb, respectively. The AFB1 concentrations ranged from 0.09 to 50.68 ppb, while the AFB2 concentrations ranged between 0.33 and 9.23 ppb. The findings showed that six isolates produced more AFB1 and AFB2 than the acceptable limit of 5 ppb. The incidence of aflatoxigenic isolates of A. flavus in sweet corn and higher concentrations of AFB1 and AFB2 emphasize the need for field trials to explore their real potential for AF production in corn.

Eco-friendly scouring of ramie fibers using crude xylano-pectinolytic enzymes for textile purpose

This study was carried out to demonstrate the biotechnological potential of xylano-pectinolytic enzymes on scouring of ramie fibers. Optimization of bioscouring process showed a maximum effect of enzymes with 50-mM strength of buffer, pH 8.5, fibers to liquid ratio of 1 : 20 (g:ml). Xylanase and pectinase dosage of 7.5 and 3.0 IU, respectively, was found to be best for removal of xylan and pectin impurities, after treatment time of 1.5 h, at 50 °C temperature and 55 rpm agitation rate. EDTA and Tween 80 at concentration of 1.5 mM and 1.25 %, respectively, were found to be the best for effective removal of impurities, in order to improve hydrophilicity of the fibers. After bioscouring, brightness and whiteness values of bioscoured fibers were increased by 9.72 and 7.10% in comparison with control fibers. After enzymatic scouring, a reduction of 14.45 % in yellowness was also seen in ramie fibers. Enzymatic treatment resulted in 6.97% increased brightness, 10.64% increased whiteness, and 4.11% decreased yellowness as compared with scoured ramie fibers. The results indicated that scouring using xylanase and pectinase enzymes could be a substitute for chemical scouring technique. Enzymatic scouring is, therefore, environmentally sustainable and saves energy, also decreases the consumption of harmful chemicals used in alkaline scouring. This is the first report showing the effect of xylanase and pectinase enzymes, produced by a bacterial isolate, on physico-chemical and various optical properties of ramie fibers.

Bio-degumming of banana fibers using eco-friendly crude xylano-pectinolytic enzymes

In this study, the efficacy of xylano-pectinolytic enzymes in scouring of banana fibers has been reported. Maximum efficiency of bioscouring was recorded using xylanase and pectinase doses of 15 and 4.8 IU, respectively (produced by a bacterial isolate) at a material-to-liquor proportion of 1:25 having 8.5 pH, treatment time of 1 h, speed of 50 rpm, temperature 50 °C, 3 mM EDTA and 1% Tween-80, with maximum sugar release, enhanced fiber water absorbing power and the finest optical characteristics. Enzymatic treatment resulted in 13.27% increase in whiteness, 16.14% increase in brightness and 8.63% decrease in yellowness as compared to raw banana fibers. The bioscouring also resulted in 50% reduction in scouring chemicals, in order to achieve the similar optical characteristics as obtained by the chemically treated fibers with 100% scouring and bleaching. It decreased the consumption of environment polluting chemicals and energy. Therefore, this has proven to be an environment safe method for removing the non-cellulosic impurities. This is the first report mentioning the scouring of banana fibers using xylano-pectinolytic enzymes.

A novel and cost-effective methodology for enhanced production of industrially valuable alkaline xylano-pectinolytic enzymes cocktail in short solid-state fermentation cycle

The aim of this study was to enhance the production of xylano-pectinolytic enzymes concurrently and also to reduce the fermentation period. In this study, the effect of agro-residues extract-based inoculum on yield and fermentation time of xylano-pectinolytic enzymes was studied. Microbial inoculum and fermentation media were supplemented with xylan and pectin polysaccharides derived from agro-based residues. Enzymes production parameters were optimized through two-stage statistical design approach. Under optimized conditions (temperature 37°C, pH 7.2, K₂ HPO₄ 0.22%, MgSO₄ 0.1%, gram flour 5.6%, substrate: moisture ratio 1:2, inoculum size 20%, agro-based crude xylan in production media 0.45%, and agro-based crude xylan-pectin in inoculum 0.13%), nearly 28,255 ± 565 and 9,202 ± 193 IU of xylanase and pectinase, respectively, were obtained per gram of substrate in a time interval of 6 days only. The yield of both xylano-pectinolytic enzymes was enhanced along with a reduction of nearly 24 h in fermentation time in comparison with control, using polysaccharides extracted from agro-residues. The activity of different types of pectinase enzymes such as exo-polymethylgalacturonase (exo-PMG), endo-PMG, exo-polygalacturonase (exo-PG), endo-PG, pectin lyase, pectate lyase, and pectin esterase was obtained as 1,601, 12.13, 5637, 24.86, 118.62, 124.32, and 12.56 IU/g, respectively, and was nearly twofold higher than obtained for all seven types in control samples. This is the first report mentioning the methodology for enhanced production of xylano-pectinolytic enzymes in short solid-state fermentation cycle using agro-residues extract-based inoculum and production media.

Genome sequence and comparative analyses of atoxigenic Aspergillus flavus WRRL 1519

Aflatoxins are toxic secondary metabolites produced by Aspergillus flavus and a few other closely related species of Aspergillus. These highly toxigenic and carcinogenic mycotoxins contaminate global food and feed supplies, posing widespread health risks to humans and domestic animals. Field application of nonaflatoxigenic strains of A. flavus to compete against aflatoxigenic strains has emerged as one of the best management practices for reducing aflatoxins contamination, yielding successful commercial products for corn, cotton seed, and peanuts. In this study, we sequenced the genome and transcriptome of atoxigenic (does not produce aflatoxin or cyclopiazonic acid) A. flavus strain WRRL 1519 isolated from a tree nut orchard to define the genetic characteristics of the strain in relation to aflatoxigenic and other nonaflatoxigenic A. flavus strains. WRRL 1519 strain was similar to other strains in size (38.0 Mb), GC content (47.2%), number of predicted secondary metabolite gene clusters (46), and number of putative proteins (12 121). About 87.4% of the predicted proteome had high shared identity with protein sequences derived from other A. flavus genomes. However, the atoxigenic A. flavus strain WRRL 1519 had deletions, or low shared identity, for many genes in the clusters required for aflatoxins and cyclopiazonic acid (CPA) synthesis. Over half of the aflatoxin synthesis gene cluster was missing, and none of the components of the CPA gene cluster were identified with high sequence similarity. Importantly, the strain appeared to maintain functional sequences of several genes thought to be required for high infectivity. Since the ability to grow on target crop is an important attribute for a successful biocontrol agent, these results indicate that the nonaflatoxigenic A. flavus strain WRRL 1519 would be a good candidate as a biocontrol agent for reducing aflatoxin and CPA accumulation in high-value nut crops.

A sustainable and green process for scouring of cotton fabrics using xylano-pectinolytic synergism: switching from noxious chemicals to eco-friendly catalysts

The objective of this research was to develop an appropriate, eco-friendly, cost-effective bioscouring methodology for removing natural impurities from cotton fabric. Maximum bioscouring was achieved using 5.0 IU xylanase and 4.0 IU pectinase with material to liquid ratio of 1:15 in a 50 mM buffer (glycine-NaOH buffer, 1.0 mM EDTA and 1% Tween-80, pH 8.5) with a treatment time of 60 min at 50 °C and an agitation speed of 60 rpm. The bioscoured cotton fabrics showed a gain of 1.17% in whiteness, 3.23% in brightness and a reduction of 4.18% in yellowness in comparison to fabric scoured with an alkaline scouring method. Further, after bleaching, the whiteness, brightness and tensile strength of the bioscoured fabrics were increased by 2.18, 2.33 and 11.74% along with a decrease of 4.61% in yellowness of bioscoured plus bleached fabrics in comparison to chemically scoured plus bleached fabrics. From the results, it is clear that bioscouring is more efficient, energy saving and an eco-friendly process and has the potential to replace the environment-damaging scouring process with the xylano-pectinolytic bioscouring process.