Production of the natural iron chelator deferriferrichrysin from Aspergillus oryzae and evaluation as a novel food-grade antioxidant

Double knockout of two target genes via genome co-editing using a nitrate transporter gene nrtA and a putative thiamine transporter gene thiI as selectable markers in Aspergillus oryzae

Genome co-editing technology is effective in breeding filamentous fungi for applications in the fermentation industry, achieving site-directed mutagenesis, the status of non-genetically modified organisms (non-GMOs), and wild-type-like growth phenotype. Prior to this study, thiI gene was found as a selectable marker for such genome co-editing in the filamentous fungus Aspergillus oryzae, while it cannot be reused via marker recycling. Therefore, we aimed to identify another marker gene to knock out another target gene via genome co-editing in A. oryzae. In this study, we focused on the membrane transporter gene nrtA (AO090012000623), which promotes uptake of nitrate (NO3-). It is known that, in nrtA knockout strain, chlorate (ClO3-), an analog of nitrate with antifungal activity, cannot be imported into the cytosol, which enables the mutant to grow in the presence of chlorate. Based on this information, knockout of the target gene wA was attempted using both nrtA- and wA-specific single-guide RNAs via genome co-editing with KClO3 supplementation in A. oryzae laboratory strain RIB40 and industrial strain KBN616. Resultantly, wA knockout mutant was generated, and nrtA was identified as a selectable marker. Moreover, this genome co-editing system using nrtA was compatible with that using thiI, and thus, a double knockout mutant of two target genes wA and yA was constructed in RIB40 while maintaining non-GMO status and wild-type-like growth. As nrtA homologs have been found in several industrial Aspergillus species, genome co-editing using homolog genes as selectable markers is plausible, which would contribute to the widespread breeding of industrial strains of Aspergilli.

The iron chelator deferriferrichrysin induces paraptosis via extracellular signal-related kinase activation in cancer cells

Cancer cells generally exhibit increased iron uptake, which contributes to their abnormal growth and metastatic ability. Iron chelators have thus recently attracted attention as potential anticancer agents. Here, we show that deferriferrichrysin (Dfcy), a natural product from Aspergillus oryzae acts as an iron chelator to induce paraptosis (a programmed cell death pathway characterized by ER dilation) in MCF-7 human breast cancer cells and H1299 human lung cancer cells. We first examined the anticancer efficacy of Dfcy in cancer cells and found that Dfcy induced ER dilation and reduced the number of viable cells. Extracellular signal-related kinase (ERK) was activated by Dfcy treatment, and the MEK inhibitor U0126, a small molecule commonly used to inhibit ERK activity, prevented the increase in ER dilation in Dfcy-treated cells. Concomitantly, the decrease in the number of viable cells upon treatment with Dfcy was attenuated by U0126. Taken together, these results demonstrate that the iron chelator Dfcy exhibits anticancer effects via induction of ERK-dependent paraptosis.

Microbial siderophores as molecular shuttles for metal cations: sources, sinks and application perspectives

Iron is one of the highly abundant elements on the earth's crust, an essential micronutrient for a majority of life forms, and exists in two frequent oxidation states such as ferrous (Fe2+) and ferric (Fe3+). These two oxidation states are interconvertible by redox reactions and form complexes with a wide range of siderophores. At neutral pH in soil, Fe2+ is highly soluble upto 100 mM but have less biological value, whereas Fe3+ is less soluble upto 10-9 M. This reduced bioavailability of Fe3+ induces competition among microorganisms. As many microorganisms need at least 10-6 M of Fe3+ form of iron for their growth, siderophores from these microbes readily withdraw Fe3+ iron from a variety of habitats for their survival. In this review, we bring into light the several recent investigations related to diverse chemistry of microbial siderophores, mechanisms of siderophore uptake, biosynthetic gene clusters in microbial genomes, various sources of heavy metal cations in soil, siderophore-binding protein receptors and commercialisation perspectives of siderophores. Besides, this review unearths the recent advancements in the characterisation of novel siderophores and its heavy metal complexes alongside the interaction kinetics with receptors.

Medical Application of Substances Derived from Non-Pathogenic Fungi Aspergillus oryzae and A. luchuensis-Containing Koji

Although most fungi cause pathogenicity toward human beings, dynasties of the East Asian region have domesticated and utilized specific fungi for medical applications. The Japanese dynasty and nation have domesticated and utilized koji fermented with non-pathogenic fungus Aspergillus oryzae for more than 1300 years. Recent research has elucidated that koji contains medicinal substances such as Taka-diastase, acid protease, koji glycosylceramide, kojic acid, oligosaccharides, ethyl-α-d-glucoside, ferulic acid, ergothioneine, pyroglutamyl leucine, pyranonigrin A, resistant proteins, deferriferrichrysin, polyamines, Bifidobacterium-stimulating peptides, angiotensin I-converting enzyme inhibitor peptides, 14-dehydroergosterol, beta-glucan, biotin, and citric acid. This review introduces potential medical applications of such medicinal substances to hyperlipidemia, diabetes, hypertension, cardiovascular and cognitive diseases, chronic inflammation, epidermal permeability barrier disruption, coronavirus disease 2019 (COVID-19), and anti-cancer therapy.

Identification of a novel pyrithiamine resistance marker gene thiI for genome co-editing in Aspergillus oryzae

Marker genes are essential for gene modification and genome editing of microorganisms. In Aspergillus oryzae, a widely used host for enzyme production, only a few marker genes can be used for positive selection. One of these genes, the pyrithiamine (PT) resistance marker gene thiA, is not useful for CRISPR/Cas9 genome editing because of its unique resistance-conferring mechanism. In this study, a novel PT resistance marker was investigated considering its potential applications in genome editing. A mutant resistant to PT was selected from UV-mutagenized A. oryzae RIB40. Whole genome analysis was conducted on the mutants, and a novel candidate gene for PT resistance was identified. This candidate gene exhibited similarity to the thiamine transporter gene thi9 of Schizosaccharomyces pombe and was designated as thiI. A thiI loss-of-function mutant was generated using the CRISPR/Cas9 genome editing system to investigate its effect on PT resistance. This mutant showed PT resistance and exhibited no growth defect or auxotrophy. The thiI gene was further investigated for its use as a selection marker in genome co-editing. Ribonucleoprotein complex comprising recombinant Cas9 nuclease and sgRNA targeting thiI or another target gene (wA or sreA) was prepared and simultaneously introduced into A. oryzae RIB40. thiI and target gene double loss-of-function mutants were efficiently selected on PT-containing medium. thiI was shown to be a useful marker gene in A. oryzae for use in genome editing. This study is expected to provide insights, which will promote basic research and industrial applications of A. oryzae.

Synthesis, physicochemical properties, and health aspects of structured lipids: A review

Structured lipids (SLs) refer to a new type of functional lipids obtained by chemically, enzymatically, or genetically modifying the composition and/or distribution of fatty acids in the glycerol backbone. Due to the unique physicochemical characteristics and health benefits of SLs (for example, calorie reduction, immune function improvement, and reduction in serum triacylglycerols), there is increasing interest in the research and application of novel SLs in the food industry. The chemical structures and molecular architectures of SLs define mainly their physicochemical properties and nutritional values, which are also affected by the processing conditions. In this regard, this holistic review provides coverage of the latest developments and applications of SLs in terms of synthesis strategies, physicochemical properties, health aspects, and potential food applications. Enzymatic synthesis of SLs particularly with immobilized lipases is presented with a short introduction to the genetic engineering approach. Some physical features such as solid fat content, crystallization and melting behavior, rheology and interfacial properties, as well as oxidative stability are discussed as influenced by chemical structures and processing conditions. Health-related considerations of SLs including their metabolic characteristics, biopolymer-based lipid digestion modulation, and oleogelation of liquid oils are also explored. Finally, potential food applications of SLs are shortly introduced. Major challenges and future trends in the industrial production of SLs, physicochemical properties, and digestion behavior of SLs in complex food systems, as well as further exploration of SL-based oleogels and their food application are also discussed.

Separation, biochemical characterization and salt-tolerant mechanisms of alkaline protease from Aspergillus oryzae

BACKGROUND

The salt tolerance of proteases secreted by Aspergillus oryzae 3.042 closely relates to the utilization of raw materials and the quality of soy sauce. However, little is known about the salt-tolerant proteases and their salt-tolerant mechanisms.

RESULTS

In this study, we isolated and identified a salt-tolerant alkaline protease (AP, approximately 29 kDa) produced by A. oryzae 3.042. It was considered as a metal-ion-independent serine protease. The optimum and stable pH values were both pH 9.0 and the optimum temperature was 40 °C. Over 20% relative activity of AP remained in the presence of 3.0 mol L^-1 NaCl after 7 days, but its K_m and V_max were only mildly influenced by the presence of 3.0 mol L^-1 NaCl, indicating its outstanding salt tolerance. Furthermore, AP was more stable than non-salt-tolerant protease at high salinity. The salt-tolerant mechanisms of AP could be due to more salt bridges, higher proportion of ordered secondary structures and stronger hydrophobic amino acid residues in the interior.

CONCLUSIONS

The above results are vital for maintaining, activating and/or modulating the activity of AP in high-salt environments. They would also provide theoretical guidance for the modification of AP and the engineering of A. oryzae 3.042 so as to secrete more AP. © 2018 Society of Chemical Industry.

Siderophores: From natural roles to potential applications

Siderophores are secondary metabolites produced by different organisms in order to scavenge iron from their surrounding environment making this essential element available to the cell. Presenting high affinity for ferric iron, siderophores are secreted out to form soluble ferric complexes that can be taken up by the organisms. Siderophores present complex chemistry that allows them to form the strongest iron-chelating complexes. Interest in this field is always up to date and new siderophores are found with new roles and applications. For example, siderophores participate to the mobilization of iron and other elements and are involved in virulence processes. Recently, a strong relation between siderophores and oxidative stress tolerance has been also highlighted. Their application in medicine has been widely studied as well as in agriculture. However, new fields are paying attention to the use of siderophores as green-iron chelators. In particular, siderophores have been proposed for the preservation of cultural heritage.

Biotechnology of siderophores in high-impact scientific fields

Different aspects of bacterial and fungal siderophore biotechnological applications will be discussed. Areas of application presented include, but are not limited to agriculture, medicine, pharmacology, bioremediation, biodegradation and food industry. In agriculture-related applications, siderophores could be employed to enhance plant growth due to their uptake by rhizobia. Siderophores hindered the presence of plant pathogens in biocontrol strategies. Bioremediation studies on siderophores discuss mostly the mobilization of heavy metals and radionuclides; the emulsifying effects of siderophore-producing microorganisms in oil-contaminated environments are also presented. The different applications found in literature based in medicine and pharmacological approaches range from iron overload to drug delivery systems and, more recently, vaccines. Additional research should be done in siderophore production and their metabolic relevance to have a deeper understanding for future biotechnological advances.