Regulation of gliotoxin biosynthesis and protection in Aspergillus species.

Aspergillus fumigatus causes a range of human and animal diseases collectively known as aspergillosis. A. fumigatus possesses and expresses a range of genetic determinants of virulence, which facilitate colonisation and disease progression, including the secretion of mycotoxins. Gliotoxin (GT) is the best studied A. fumigatus mycotoxin with a wide range of known toxic effects that impair human immune cell function. GT is also highly toxic to A. fumigatus and this fungus has evolved self-protection mechanisms that include (i) the GT efflux pump GliA, (ii) the GT neutralising enzyme GliT, and (iii) the negative regulation of GT biosynthesis by the bis-thiomethyltransferase GtmA. The transcription factor (TF) RglT is the main regulator of GliT and this GT protection mechanism also occurs in the non-GT producing fungus A. nidulans. However, the A. nidulans genome does not encode GtmA and GliA. This work aimed at analysing the transcriptional response to exogenous GT in A. fumigatus and A. nidulans, two distantly related Aspergillus species, and to identify additional components required for GT protection. RNA-sequencing shows a highly different transcriptional response to exogenous GT with the RglT-dependent regulon also significantly differing between A. fumigatus and A. nidulans. However, we were able to observe homologs whose expression pattern was similar in both species (43 RglT-independent and 11 RglT-dependent). Based on this approach, we identified a novel RglT-dependent methyltranferase, MtrA, involved in GT protection. Taking into consideration the occurrence of RglT-independent modulated genes, we screened an A. fumigatus deletion library of 484 transcription factors (TFs) for sensitivity to GT and identified 15 TFs important for GT self-protection. Of these, the TF KojR, which is essential for kojic acid biosynthesis in Aspergillus oryzae, was also essential for virulence and GT biosynthesis in A. fumigatus, and for GT protection in A. fumigatus, A. nidulans, and A. oryzae. KojR regulates rglT, gliT, gliJ expression and sulfur metabolism in Aspergillus species. Together, this study identified conserved components required for GT protection in Aspergillus species.

Development of an itraconazole resistance gene as a dominant selectable marker for transformation in Aspergillus oryzae and Aspergillus luchuensis.

There are only a few combinations of antifungal drugs with known resistance marker genes in the Aspergillus species; therefore, the transformation of their wild-type strains is limited. In this study, to develop the novel dominant selectable marker for itraconazole, a fungal cell membrane synthesis inhibitor, we focused on Aspergillus luchuensis cyp51A (Alcyp51A), which encodes a 14-α-sterol demethylase related to the steroid synthesis pathway. We found that the G52R mutation in AlCyp51A and the replacement of the native promoter with a high-expression promoter contributed to itraconazole resistance in Aspergillus oryzae, designated as itraconazole resistant gene (itrA). The random integration in the A. luchuensis genome of the itrA marker cassette gene also allowed for transformation using itraconazole. Therefore, we succeed in developing a novel itraconazole resistance marker as a dominant selectable marker for transformation in A. oryzae and A. luchuensis.

Antimicrobial activity and secondary structure of a novel peptide derived from ovalbumin.

A novel antimicrobial peptide derived from ovalbumin has been discovered. First, the peptide fragment RKIKVYLPRMK (TK9.1) was identified based on computerized predictions of the secondary structure of peptides in a protein data bank. Using HeliQuest, the sequence was developed into RKIKRYLRRMI (TK9.1.3), which was synthesized using Fmoc-solid phase peptide synthesis, and found to have strongly antimicrobial activity against Gram-positive and Gram-negative bacteria, and fungi but not cytotoxic to HeLa cells and hemolysis in mouse red blood cells. Although ovalbumin itself does not have an antibacterial activity, our results suggest that it may supply the organisms that consume it with antimicrobial peptides, in support of their immunodefence.

The rational design, synthesis, and antimicrobial investigation of 2-Amino-4-Methylthiazole analogues inhibitors of GlcN-6-P synthase.

A series of novel 2-Amino-4-Methylthiazole analogs were developed via three-step reaction encompassing hydrazine-1-carboximidamide motif to combat Gram-positive and Gram-negative bacterial and fungal infections. Noticeably, the thiazole-carboximidamide derivatives 4a-d displayed excellent antimicrobial activity and the most efficacious analogue 4d with MIC/MBC values of 0.5 and 4 µg/mL, compared to reference drugs with very low toxicity to mammalian cells, resulting in a prominent selectivity more than 100 folds. Microscopic investigation of 4d biphenyl analogue showed cell wall lysis and promote rapid bactericidal activity though disrupting the bacterial membrane. In addition, an interesting in vitro investigation against GlcN-6-P Synthase Inhibition was done which showed potency in the nanomolar range. Meanwhile, this is the first study deploying a biomimicking strategy to design potent thiazole-carboximidamides that targeting GlcN-6-P Synthase as antimicrobial agents. Importantly, Molecular modeling simulation was done for the most active 4d analogue to study the interaction of this analogue which showed good binding propensity to glucosamine binding site which support the in vitro data.

The PDR-type ABC transporters AtrA and AtrG are involved in azole drug resistance in Aspergillus oryzae.

For strain improvement of Aspergillus oryzae, development of the transformation system is essential, wherein dominant selectable markers, including drug-resistant genes, are available. However, A. oryzae generally has a relatively high resistance to many antifungal drugs effective against yeasts and other filamentous fungi. In the course of the study, while investigating azole drug resistance in A. oryzae, we isolated a spontaneous mutant that exhibited high resistance to azole fungicides and found that pleiotropic drug resistance (PDR)-type ATP-binding cassette (ABC) transporter genes were upregulated in the mutant; their overexpression in the wild-type strain increased azole drug resistance. While deletion of the gene designated atrG resulted in increased azole susceptibility, double deletion of atrG and another gene (atrA) resulted in further azole hypersensitivity. Overall, these results indicate that the ABC transporters AtrA and AtrG are involved in azole drug resistance in A. oryzae.

Enhanced production of fructosyltransferase in Aspergillus oryzae by genome shuffling.

OBJECTIVE: To breed Aspergillus oryzae strains with high fructosyltransferase (FTase) activity using intraspecific protoplast fusion via genome-shuffling. RESULTS: A candidate library was developed using UV/LiCl of the conidia of A. oryzae SBB201. By screening for enzyme activity and cell biomass, two mutants (UV-11 and UV-76) were chosen for protoplast fusion and subsequent genome shuffling. After three rounds of genome recombination, a fusion mutant RIII-7 was obtained. Its FTase activity was 180 U g-1, approximately double that of the original strain, and RIII-7 was genetically stable. In fermentation culture, FTase activity of the genome-shuffled strain reached a maximum of 353 U g-1 using substrate-feeding method, and this value was approximately 3.4-times higher than that of the original strain A. oryzae SBB201. CONCLUSIONS: Intraspecific protoplast fusion of A. oryzae significantly enhanced FTase activity and generated a potentially useful strain for industrial production.

Identification and functional analysis of a new glyphosate resistance gene from a fungus cDNA library.

Glyphosate is a widely used broad spectrum herbicide; however, this limits its use once crops are planted. If glyphosate-resistant crops are grown, glyphosate can be used for weed control in crops. While several glyphosate resistance genes are used in commercial glyphosate tolerant crops, there is interest in identifying additional genes for glyphosate tolerance. This research constructed a high-quality cDNA library form the glyphosate-resistant fungus Aspergillus oryzae RIB40 to identify genes that may confer resistance to glyphosate. Using a medium containing glyphosate (120mM), we screened several clones from the library. Based on a nucleotide sequence analysis, we identified a gene of unknown function (GenBank accession number: XM_001826835.2) that encoded a hypothetical 344-amino acid protein. The gene was named MFS40. Its ORF was amplified to construct an expression vector, pGEX-4T-1-MFS40, to express the protein in Escherichia coli BL21. The gene conferred glyphosate tolerance to E. coli ER2799 cells.

Structure activity relationship study of burkholdine analogues toward simple antifungal agents.

Cyclic and linear lipopeptides, burkholdine analogues, were synthesized by conventional Fmoc-SPPS and cyclisation with DIPC/HOBt in the solution phase. Synthesized peptides were evaluated for antifungal activities with MIC values against Saccharomyces cerevisiae and Aspergillus oryzae. As a result, the stereochemistry of the amino acid residues and sequences of burkholdine analogues exerted a significant influence on antifungal activities. In addition, we found a linear burkholdine analogue with moderate antifungal activities.

Galacto configured N-aminoaziridines: a new type of irreversible inhibitor of ß-galactosidases.

A new type of galactose mimetics has been synthesized following a straightforward synthetic approach based on cyclohexene olefin aziridination reactions directed by hydroxyl substituents. These enantiomerically pure galacto-configured N-aminoaziridines are potent irreversible inhibitors of Aspergillus oryzae and Escherichia coliß-galactosidases.

Establishment of a new method to quantitatively evaluate hyphal fusion ability in Aspergillus oryzae.

Hyphal fusion is involved in the formation of an interconnected colony in filamentous fungi, and it is the first process in sexual/parasexual reproduction. However, it was difficult to evaluate hyphal fusion efficiency due to the low frequency in Aspergillus oryzae in spite of its industrial significance. Here, we established a method to quantitatively evaluate the hyphal fusion ability of A. oryzae with mixed culture of two different auxotrophic strains, where the ratio of heterokaryotic conidia growing without the auxotrophic requirements reflects the hyphal fusion efficiency. By employing this method, it was demonstrated that AoSO and AoFus3 are required for hyphal fusion, and that hyphal fusion efficiency of A. oryzae was increased by depleting nitrogen source, including large amounts of carbon source, and adjusting pH to 7.0.

Enhanced ß-galactosidase production of Aspergillus oryzae mutated by UV and LiCl.

In order to breed a high-yield ß-galactosidase-producing strain, Aspergillus oryzae was used as the parent strain and mutagenized with ultraviolet (UV) and UV plus lithium chloride (LiCl), respectively. After being mutagenized by UV, the ß-galactosidase activity of mutant UV-15-20 reached 114.08 U/mL, which revealed a 49.22% increase compared with the original strain. A mutant UV-LiCl-38 with high ß-galactosidase activity (121.42 U/mL) was obtained after compound mutagenesis of UV and LiCl; the ß-galactosidase activity of this mutant was 58.82% higher than that of the parent strain. Subculture testing indicated that UV-15-20 and UV-LiCl-38 had good hereditary stability and may be ideal strains for the production of ß-galactosidase. Additionally, it was demonstrated that compound mutagenesis with UV and LiCl is an effective mutation method for breeding industrially interesting strains.

Alpha-momorcharin, a RIP produced by bitter melon, enhances defense response in tobacco plants against diverse plant viruses and shows antifungal activity in vitro.

Alpha-momorcharin (α-MMC) is type-1 ribosome inactivating proteins (RIPs) with molecular weight of 29 kDa and has lots of biological activity. Our recent study indicated that the α-MMC purified from seeds of Momordica charantia exhibited distinct antiviral and antifungal activity. Tobacco plants pre-treated with 0.5 mg/mL α-MMC 3 days before inoculation with various viruses showed less-severe symptom and less reactive oxygen species (ROS) accumulation compared to that inoculated with viruses only. Quantitative real-time PCR analysis revealed that the replication levels of viruses were lower in the plants treated with the α-MMC than control plants at 15 days post inoculation. Moreover, the coat protein expression of viruses was almost completely inhibited in plants which were treated with the α-MMC compared with control plants. Furthermore, the SA-responsive defense-related genes including non-expressor of pathogenesis-related genes 1 (NPR1), PR1, PR2 were up-regulated and activities of some antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) were increased after the α-MMC treatment. In addition, the α-MMC (500 µg/mL) revealed remarkable antifungal effect against phytopathogenic fungi, in the growth inhibition range 50.35-67.21 %, along with their MIC values ranging from 100 to 500 µg/mL. The α-MMC had also a strong detrimental effect on spore germination of all the tested plant pathogens along with concentration as well as time-dependent kinetic inhibition of Sclerotinia sclerotiorum. The α-MMC showed a remarkable antiviral and antifungal effect and hence could possibly be exploited in crop protection for controlling certain important plant diseases.

Synthesis and antifungal activities of cyclic octa-lipopeptide burkholdine analogues.

Synthesis and antifungal activity of cyclic octapeptide derivatives of burkholdines are described. To construct cyclic octapeptides, the combination of Fmoc-SPPS and cyclization with DIC/HOBt in the solution phase was employed. Synthesized peptides were evaluated for antifungal activity with MIC values against Saccharomyces cerevisiae, Aspergillus oryzae, and Candida viswanathii. As a result, the lipid side chain and the stereochemistry of each amino acid of Bk-1097 analogues significantly affected antifungal activity.

Synthesis of novel 2-amino-4-(5'-substituted 2'-phenyl-1H-indol-3'-yl)-6-aryl-4H-pyran-3-carbonitrile derivatives as antimicrobial and antioxidant agents.

As a part of systematic investigation of synthesis and biological activities of indole analogues linked to various heterocyclic systems, we have synthesized new compounds viz., 2-amino-4-(5'-substituted 2'-phenyl-1H-indol-3'-yl)-6-aryl-4H-pyran-3-carbonitriles (2a-i), 4,5-diamino-6-(5'-substituted 2'-phenyl-1H-indol-3'-yl)-8-aryl-2-oxo-2,6-dihydrodipyrano [2,3-b:3,2-e]pyridine-3-carbonitriles (3a-i), 4-amino-5-(5'-substituted 2'-phenyl-1H-indol-3-yl)-7-aryl-1H-pyrano[2,3-d]pyrimidin-2(5H)-ones (4a-i), 4-amino-5-(5'-substituted 2'-phenyl-1H-indol-3'-yl)-7-aryl-1H-pyrano[2,3-d]pyrimidin-2(5H)-thiones (5a-i), 4-(5'-subtituted 2'-phenyl-1H-indol-3'-yl)-6-aryl-1,4-dihydropyrano[2,3-c]pyrazol-3-amines (6a-i) and 5-(5'-substituted 2'-phenyl-1H-indol-3'-yl)-7-aryl-3H-pyrano[2,3-d]pyrimidin-4(5H)-ones (7a-i). Antibacterial activity results revealed that, compound 6a showed promising activity versus Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae. Compound 6d exhibited good activity against S. aureus, K. pneumoniae and Pseudomonas aeruginosa. Antifungal activity results indicated that, compound 4d exhibited maximum zone of inhibition against Aspergillus oryzae and Aspergillus flavus. In case of antioxidant activity, compound 4a showed promising radical scavenging activity, ferric ions (Fe(3+)) reducing antioxidant power (FRAP) and metal chelating activity.

Improved production of protease-resistant phytase by Aspergillus oryzae and its applicability in the hydrolysis of insoluble phytates.

Among three hundred isolates of filamentous fungi, Aspergillus oryzae SBS50 secreted higher phytase activity at pH 5.0, 35 °C and 200 rpm after 96 h of fermentation. Starch and beef extract supported the highest phytase production than other carbon and nitrogen sources. A nine-fold improvement in phytase production was achieved due to optimization. Supplementation of the medium with inorganic phosphate repressed the enzyme synthesis. Among surfactants tested, Tween 80 increased fungal growth and phytase production, which further resulted in 5.4-fold enhancement in phytase production. The phytase activity was not much affected by proteases treatment. The enzyme resulted in the efficient hydrolysis of insoluble phytate complexes (metal- and protein-phytates) in a time dependent manner. Furthermore, the hydrolysis of insoluble phytates was also supported by scanning electron microscopy. The enzyme, being resistant to trypsin and pepsin, and able to hydrolyze insoluble phytates, can find an application in the animal food/feed industry for improving nutritional quality and also in combating environmental phosphorus pollution and plant growth promotion.

A further study on chromosome minimization by protoplast fusion in Aspergillus oryzae.

Our goal in this work was to develop a method to minimize the chromosomes of Aspergillus oryzae, to arrive at a deeper understanding of essential gene functions that will help create more efficient industrially useful strains. In a previous study, we successfully constructed a highly reduced chromosome 7 using multiple large-scale chromosomal deletions (Jin et al. in Mol Genet Genomics 283:1-12, 2010). Here, we have created a further reduced chromosome A. oryzae mutant harboring a reduced chromosome 7 and a reduced chromosome 8 both of which contain a large number of non-syntenic blocks. These are the smallest A. oryzae chromosomes that have been reported. Protoplast fusion between the two distinct chromosome-reduced mutants produced a vigorous and stable fusant which was isolated. PCR and flow cytometry confirmed that two kinds of nuclei, derived from the parent strains, existed in this fusant and that the chromosome DNA per nucleus was doubled, suggesting that the fusant was a heterozygous diploid strain. By treating the cell with 1 µg/ml benomyl, cell nuclei haploidization was induced in the stable diploid strain. Array comparative genomic hybridization and pulsed-field gel electrophoresis confirmed that the reduced chromosomes 7 and 8 co-existed in the haploid fusant and that no other chromosomal modifications had occurred. This method provides a useful tool for chromosome engineering in A. oryzae to construct an industry-useful strain.

Indigestible dextrin is an excellent inducer for α-amylase, α-glucosidase and glucoamylase production in a submerged culture of Aspergillus oryzae.

α-Amylase activities of Aspergillus oryzae grown on dextrin or indigestible dextrin were 7·8 and 27·7 U ml(-1), respectively. Glucoamylase activities of the cultures grown on dextrin or indigestible dextrin were 5·4 and 301 mU ml(-1), respectively. The specific glucoamylase production rate in indigestible dextrin batch culture reached 1·35 U g DW(-1) h(-1). In contrast, biomass concentration of A. oryzae in indigestible dextrin culture was 35% of that in dextrin culture. Thus, the culture method using indigestible dextrin has the potential to improve amylolytic enzyme production and fungal fermentation broth rheology.

Effect of chlorhexidine gluconate on mechanical and anti-microbial properties of thermoplastic cassava starch.

Antimicrobial thermoplastic starch (TPS) was developed using cassava starch, glycerol, and chlorhexidine gluconate (CHG) blend. CHG was added at concentrations of 1%, 5%, 10%, and 20% (wt./wt.) as an antimicrobial additive. The tensile strength and hardness of the blended samples increased with the chlorhexidine gluconate content, especially for 1% CHG. wt./wt. (12.6 MPa and 94, respectively). The TPS/CHG20 blend exhibited a large phase of CHG and recrystallization of TPS. The water solubility decreased with the addition of CHG. Nuclear magnetic resonance data confirmed a reaction between the hydroxyl groups of TPS and the amino groups of CHG. The TPS/CHG20% exhibited an inhibition zone for three bacterial types (Staphylococcus aureus, Escherichia coli, and Bacillus cereus) and three fungal types (Rhizopus oligosporus, Aspergillus oryzae, and Candida albicans). CHG acted simultaneously as a chain extender and an antimicrobial additive for TPS, improving its tensile strength, hardness, and anti-microbial properties.

MS/MS fragmentation-guided search of TMG-chitooligomycins and their structure-activity relationship in specific ß-N-acetylglucosaminidase inhibition.

The reducing tetrasaccharide TMG-chitotriomycin (1) is an inhibitor of ß-N-acetylglucosaminidase (GlcNAcase), produced by the actinomycete Streptomyces anulatus NBRC13369. The inhibitor shows a unique inhibitory spectrum, that is, selectivity toward enzymes from chitin-containing organisms such as insects and fungi. Nevertheless, its structure-selectivity relationship remains to be clarified. In this study, we conducted a structure-guided search of analogues of 1 in order to obtain diverse N,N,N-trimethylglucosaminium (TMG)-containing chitooligosaccharides. In this approach, the specific fragmentation profile of 1 on ESI-MS/MS analysis was used for the selective detection of desired compounds. As a result, two new analogues, named TMG-chitomonomycin (3) and TMG-chitobiomycin (2), were obtained from a culture filtrate of 1-producing Streptomyces. Their enzyme-inhibiting activity revealed that the potency and selectivity depended on the degree of polymerization of the reducing end GlcNAc units. Furthermore, a computational modeling study inspired the inhibitory mechanism of TMG-related compounds as a mimic of the substrate in the Michaelis complex of the GH20 enzyme. This study is an example of the successful application of a MS/MS experiment for structure-guided isolation of natural products.

Five carboxin-resistant mutants exhibited various responses to carboxin and related fungicides.

Five carboxin-resistant mutants from Aspergillus oryzae were characterized by the sensitivities of their mycelial growth and succinate dehydrogenase (SDH) activity to carboxin and three related fungicides. Despite a significant resistance to carboxin, exhibited by all the mutants, their patterns of sensitivity to the other fungicides was distinct. This provides clues to the molecular interaction between SDH and these fungicides.