Differentiation and quantification of the ochratoxin A producers Aspergillus ochraceus and Aspergillus westerdijkiae using PCR-DGGE

Endoglucanase H from Aspergillus westerdijkiae Plays an Important Role in the Virulence on Pear Fruits

Aspergillus westerdijkiae can infect many agricultural products including cereals, grapes, and pear. Pathogenic fungi secrete diverse effectors as invasive weapons for successful invasion the host plant. During the pathogen-host interaction, 4486 differentially expressed genes were observed in A. westerdijkiae with 2773 up-regulated and 1713 down-regulated, whereas 8456 differentially expressed genes were detected in pear fruits with 4777 up-regulated and 3679 down-regulated. A total of 309 effector candidate genes were identified from the up-regulated genes in A. westerdijkiae. Endoglucanase H (AwEGH) was significantly induced during the pathogen-host interaction. Deletion of AwEGH resulted in altered fungal growth and morphology and reduced conidia production and germination compared to the wild-type. Further experiments demonstrated that AwEGH plays a role in cell wall integrity. Importantly, disruption of AwEGH significantly reduced the fungal virulence on pear fruits, and this defect can be partly explained by the impaired ability of A. westerdijkiae to penetrate host plants.

The Secondary Metabolites and Biosynthetic Diversity From Aspergillus ochraceus

Aspergillus ochraceus, generally known as a food spoilage fungus, is the representative species in Aspergillus section Circumdati. A. ochraceus strains are widely distributed in nature, and usually isolated from cereal, coffee, fruit, and beverage. Increasing cases suggest A. ochraceus acts as human and animal pathogens due to producing the mycotoxins. However, in terms of benefits to mankind, A. ochraceus is the potential source of industrial enzymes, and has excellent capability to produce diverse structural products, including polyketides, nonribosomal peptides, diketopiperazine alkaloids, benzodiazepine alkaloids, pyrazines, bis-indolyl benzenoids, nitrobenzoyl sesquiterpenoids, and steroids. This review outlines recent discovery, chemical structure, biosynthetic pathway, and bio-activity of the natural compounds from A. ochraceus.

The effect of cold atmospheric pressure plasma on Aspergillus ochraceus and ochratoxin A production

Aspergillus ochraceus is a soil fungus known to produce ochratoxin A, a harmful secondary metabolite. Prevention and control of fungal pathogens mostly rely on chemical fungicides, which is one of the contributing factors in the emergence of the fungal resistance, hence novel methods for fungal eradication have been extensively researched. The cold atmospheric pressure (CAP) plasma generated in ambient air has been recently applied in microbial decontamination. Here we used the diffuse coplanar surface barrier discharge in inactivation of a toxigenic strain A. ochraceus. The plasma-treated conidia and mycelium exhibited morphological changes such as ruptures and desiccation. Mycelium dehydration and changes in the chemical composition of hyphal surface accompanied plasma treatment. The growth of 26 h old mycelia were significantly restricted after 30 s of plasma treatment. The conidial vitality declined 4 logs after 180 s of plasma exposure leading to almost complete decontamination. After shorter plasma treatment of conidia, the ochratoxin A (OTA) production increased at the early stage of cultivation, but the overall level was significantly reduced compared to untreated samples after longer cultivation. Our results indicated that the fungal growth and the OTA production were significantly changed by plasma treatment and underscored CAP plasma as a promising method in the decontamination of A. ochraceus without a risk to generate strains with increased OTA production.

DNA sequencing, genomes and genetic markers of microbes on fruits and vegetables

The development of DNA sequencing technology has provided an effective method for studying foodborne and phytopathogenic microorganisms on fruits and vegetables (F & V). DNA sequencing has successfully proceeded through three generations, including the tens of operating platforms. These advances have significantly promoted microbial whole‐genome sequencing (WGS) and DNA polymorphism research. Based on genomic and regional polymorphisms, genetic markers have been widely obtained. These molecular markers are used as targets for PCR or chip analyses to detect microbes at the genetic level. Furthermore, metagenomic analyses conducted by sequencing the hypervariable regions of ribosomal DNA (rDNA) have revealed comprehensive microbial communities in various studies on F & V. This review highlights the basic principles of three generations of DNA sequencing, and summarizes the WGS studies of and available DNA markers for major bacterial foodborne pathogens and phytopathogenic fungi found on F & V. In addition, rDNA sequencing‐based bacterial and fungal metagenomics are summarized under three topics. These findings deepen the understanding of DNA sequencing and its application in studies of foodborne and phytopathogenic microbes and shed light on strategies for the monitoring of F & V microbes and quality control.