Specific expression and temperature-dependent expression of the acid protease-encoding gene (pepA) in Aspergillus oryzae in solid-state culture (Rice-Koji)

Aspergillus oryzae PrtR alters transcription of individual peptidase genes in response to the growth environment

Aspergillus oryzae PrtR is an ortholog of the transcription factor PrtT, which positively regulates the transcription of extracellular peptidase genes in Aspergillus niger and Aspergillus fumigatus. To identify the genes under the control of PrtR and elucidate its regulatory mechanism in A. oryzae, prtR gene disruption mutants were generated. The control strain clearly showed a halo on media containing skim milk as the nitrogen source, whereas the ΔprtR strain formed a smaller halo. Measurement of acid peptidase activity revealed that approximately 84% of acidic endopeptidase and 86% of carboxypeptidase activities are positively regulated by PrtR. As the transcription of the prtR gene varied depending on culture conditions, especially with or without a protein substrate, it was considered that its transcription would be regulated in response to a nitrogen source. In addition, contrary to previous expectations, PrtR was found to act both in promoting and repressing the transcription of extracellular peptidase genes. The mode of regulation varied from gene to gene. Some genes were regulated in the same manner in both liquid and solid cultures, whereas others were regulated in different ways depending on the culture conditions. Furthermore, PrtR has been suggested to regulate the transcription of peptidase genes that are closely associated with other transcription factors. KEY POINTS: • Almost all peptidase genes in Aspergillus oryzae are positively regulated by PrtR • However, several genes are regulated negatively by PrtR • PrtR optimizes transcription of peptidase genes in response to culture conditions.

Identification and enzymatic properties of arginine decarboxylase from Aspergillus oryzae

Aspergillus oryzae spores, when sprinkled onto steamed rice and allowed to propagate, are referred to as rice "koji." Agmatine, a natural polyamine derived from arginine through the action of arginine decarboxylase (ADC), is abundantly produced by solid state-cultivated rice koji of A. oryzae RIB40 under low pH conditions, despite the apparent absence of ADC orthologs in its genome. Mass spectrometry imaging revealed that agmatine was accumulated inside rice koji at low pH conditions, where arginine was distributed. ADC activity was predominantly observed in substrate mycelia and minimally in aerial mycelia. Natural ADC was isolated from solid state-cultivated A. oryzae rice koji containing substrate mycelia, using ammonium sulfate fractionation, ion exchange, and gel-filtration chromatography. The purified protein was subjected to sodium dodecyl sulfate poly-acrylamide gel electrophoresis (SDS-PAGE), and the detected peptide band was digested for identification by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The gene AO090102000327 of strain RIB40 was identified, previously annotated as phosphatidylserine decarboxylase (PSD), and encoded a 483-amino acid peptide. Recombinant protein encoded by AO090102000327 was expressed in Escherichia coli cells cultivated at 20°C, resulting in the detection of 49 kDa and 5 kDa peptides. The protein exhibited pyruvoyl-dependent decarboxylase activity, favoring arginine over ornithine and showing no activity with phosphatidylserine. The gene was designated Ao-adc1. Ao-ADC1 expression in rice koji at pH 4-6 was confirmed through western blotting using the anti-Ao-ADC1 serum. These findings indicate that Ao-adc1 encodes arginine decarboxylase involved in agmatine production.IMPORTANCEGene AO090102000327 in A. oryzae RIB40, previously annotated as a PSD, falls into a distinct clade when examining the phylogenetic distribution of PSDs. Contrary to the initial PSD annotation, our analysis indicates that the protein encoded by AO090102000327 is expressed in the substrate mycelia area of solid state-cultivated A. oryzae rice koji and functions as an arginine decarboxylase (ADC). The clade to which Ao-ADC1 belongs includes three other Ao-ADC1 paralogs (AO090103000445, AO090701000800, and AO090701000802) that presumably encode ADC rather than PSDs. Regarding PSD, AO090012000733 and AO090005001124 were speculated to be nonmitochondrial and mitochondrial PSDs in A. oryzae RIB40, respectively.

Analysis of nitrogen source assimilation in industrial strains of Aspergillus oryzae

Nitrogen source assimilation is important for the biological functions of fungi, and its pathway has been deeply studied. Aspergillus oryzae mutants defective in nitrogen source assimilation are known to grow poorly on Czapek-Dox (CD) medium. In this study, we found an industrial strain of A. oryzae that grew very poorly on a CD medium containing sodium nitrate as a nitrogen source. We used media with various nitrogen components to examine the steps affecting the nitrogen source assimilation pathway of this strain. The strain grew well on the CD medium supplied with nitrite salt or ammonium salt, suggesting that the strain was defective in nitrate assimilation step. To ascertain the gene causing the defect of nitrate assimilation, a gene expression vector harboring either niaD or crnA of A. oryzae RIB40 was introduced into the industrial strain. The industrial strain containing the crnA vector recovered its growth. This is the first report that a mutation of crnA causes poor growth on CD medium in an industrial strain of A. oryzae, and crnA can be used as a transformation marker for crnA deficient strains.

Construction of self-cloning Aspergillus oryzae strains with high production of multiple biomass-degrading enzymes on solid-state culture

Filamentous fungi produce numerous industrially important enzymes. Among them, Aspergillus oryzae-derived enzymes are widely used in various fermentation applications. In this study, we constructed self-cloning strains that overproduce multiple biomass-degrading enzymes under the control of a strong promoter of α-amylase-coding gene (amyB) using the industrial strain A. oryzae AOK11. Two strains (strains 2-4 and 3-26) were introduced with different combinations of genes encoding xylanase (xynG1), phytase (phyA), pectin lyase (pelA), and polygalacturonase (pgaB). These strains had at least one copy of each enzyme gene derived from the expression cassette in the genome. The transcription levels of enzyme-coding genes introduced were more than 100-fold higher than those in the parent strain. Reflecting the high transcription levels, the activities of the enzymes derived from the expression cassettes of these two strains were significantly higher than those of the parent strain in both liquid and solid-state cultures. Even in ventilated solid-state cultures that were scaled up using mechanical equipment for practical applications, the two strains showed significantly higher enzyme activity than the parent strain. These results indicate that these strains constructed using a safe self-cloning technique represent industrially valuable practical strains that can be used in the food and livestock industries.

Copper ion (Cu2+) is involved in the transcription of the tyrosinase-encoding melB gene of Aspergillus oryzae in solid-state culture

In Aspergillus oryzae, the tyrosinase-encoding gene melB causes undesirable browning of sake and sake lees. This gene is known to be expressed specifically in solid-state culture; however, its expression mechanisms remain unknown. Here, we evaluated the possible factors affecting the transcription of melB and found that the copper ion (Cu2+) significantly enhanced the transcription level of melB in solid-state culture.

Regulation of nutrient utilization in filamentous fungi

Organisms must accurately sense and respond to nutrients to survive. In filamentous fungi, accurate nutrient sensing is important in the establishment of fungal colonies and in continued, rapid growth for the exploitation of environmental resources. To ensure efficient nutrient utilization, fungi have evolved a combination of activating and repressing genetic networks to tightly regulate metabolic pathways and distinguish between preferred nutrients, which require minimal energy and resources to utilize, and nonpreferred nutrients, which have more energy-intensive catabolic requirements. Genes necessary for the utilization of nonpreferred carbon sources are activated by transcription factors that respond to the presence of the specific nutrient and repressed by transcription factors that respond to the presence of preferred carbohydrates. Utilization of nonpreferred nitrogen sources generally requires two transcription factors. Pathway-specific transcription factors respond to the presence of a specific nonpreferred nitrogen source, while another transcription factor activates genes in the absence of preferred nitrogen sources. In this review, we discuss the roles of transcription factors and upstream regulatory genes that respond to preferred and nonpreferred carbon and nitrogen sources and their roles in regulating carbon and nitrogen catabolism. KEY POINTS: • Interplay of activating and repressing transcriptional networks regulates catabolism. • Nutrient-specific activating transcriptional pathways provide metabolic specificity. • Repressing regulatory systems differentiate nutrients in mixed nutrient environments.

Insights and Perspectives on the Role of Proteostasis and Heat Shock Proteins in Fungal Infections

Fungi are a diverse group of eukaryotic organisms that infect humans, animals, and plants. To successfully colonize their hosts, pathogenic fungi must continuously adapt to the host's unique environment, e.g., changes in temperature, pH, and nutrient availability. Appropriate protein folding, assembly, and degradation are essential for maintaining cellular homeostasis and survival under stressful conditions. Therefore, the regulation of proteostasis is crucial for fungal pathogenesis. The heat shock response (HSR) is one of the most important cellular mechanisms for maintaining proteostasis. It is activated by various stresses and regulates the activity of heat shock proteins (HSPs). As molecular chaperones, HSPs participate in the proteostatic network to control cellular protein levels by affecting their conformation, location, and degradation. In recent years, a growing body of evidence has highlighted the crucial yet understudied role of stress response circuits in fungal infections. This review explores the role of protein homeostasis and HSPs in fungal pathogenicity, including their contributions to virulence and host-pathogen interactions, as well as the concerted effects between HSPs and the main proteostasis circuits in the cell. Furthermore, we discuss perspectives in the field and the potential for targeting the components of these circuits to develop novel antifungal therapies.

Koji Molds for Japanese Soy Sauce Brewing: Characteristics and Key Enzymes

Soy sauce is a traditional Japanese condiment produced from the fermentation of soybeans, wheat, and salt by three types of microorganisms, namely koji molds, halophilic lactic acid bacteria, and salt-tolerant yeast. The delicate balance between taste, aroma, and color contributes to the characteristic delicious flavor imparted by soy sauce. In soy sauce brewing, protein and starch of the raw materials are hydrolyzed into amino acids and sugars by enzymes derived from koji molds. These enzymatically hydrolyzed products not only directly contribute to the taste but are further metabolized by lactic acid bacteria and yeasts to most of organic acids and aromatic compounds, resulting in its distinctive flavor and aroma. The color of the soy sauce is also due to the chemical reactions between amino acids and sugars during fermentation. Therefore, koji mold, which produces various enzymes for the breakdown of raw materials, is an essential microorganism in soy sauce production and plays an essential role in fermenting the ingredients. In this review, we describe the manufacturing process of Japanese soy sauce, the characteristics of koji molds that are suitable for soy sauce brewing, and the key enzymes produced by koji molds and their roles in the degradation of materials during soy sauce fermentation, focusing on the production of umami taste in soy sauce brewing.

Membrane traffic related to endosome dynamics and protein secretion in filamentous fungi

In eukaryotic cells, membrane-surrounded organelles are orchestrally organized spatiotemporally under environmental situations. Among such organelles, vesicular transports and membrane contacts occur to communicate each other, so-called membrane traffic. Filamentous fungal cells are highly polarized and thus membrane traffic is developed to have versatile functions. Early endosome (EE) is an endocytic organelle that dynamically exhibits constant long-range motility through the hyphal cell, which is proven to have physiological roles, such as other organelle distribution and signal transduction. Since filamentous fungal cells are also considered as cell factories, to produce valuable proteins extracellularly, molecular mechanisms of secretory pathway including protein glycosylation have been well investigated. In this review, molecular and physiological aspects of membrane traffic especially related to EE dynamics and protein secretion in filamentous fungi are summarized, and perspectives for application are also described.

Koji Starter and Koji World in Japan

Koji is made by culturing koji mold on grains. Koji has wide-ranging applications, for example, in alcoholic beverages and seasonings. The word 'mold' generally has a bad image, but in Japan, koji mold is valued for its usefulness, and over the years, efforts have been made to make safe, stable, and delicious food products from it. Koji mold spores, essential when making koji, are called koji starter in the industry. From the many available strains, those suitable for the production of each fermented food are chosen based on indicators such as growth rate and enzyme production capacity. In manufacturing using microorganisms, purity and yield are prioritized. However, the production of fermented foods using koji is more complex, with focus not only on the degree of decomposition of raw materials but also on factors influencing overall product design, including palatability, color, smell, and texture. Production can be facilitated by the variety of koji brought about by the diversity of koji mold combined with the solid culture method which increases the amount of enzyme production. In this report, we introduce the history of koji starter in Japan, the characteristics of koji mold in practice, and various fermented foods made from it. In addition, the factors affecting the quality of koji in solid culture are described.

Adjunctive application of solid-state culture products and its freeze-dried powder from Aspergillus sojae for semi-hard cheese

BACKGROUND

Species belonging to the genus Aspergillus have been used in traditional Japanese fermented foods. Aspergillus sojae is a species responsible for strong proteolytic activity. Freeze-drying treatments followed by physical disruption enables the pulverization of the mycelia of A. sojae RIB 1045 grown in whey protein-base solid media. Intracellular proteases were extracted using this protocol to compare extracellular protease activity in terms of the reaction's pH dependence in the presence or absence of inhibitors.

RESULT

With different sensitivities to inhibitors, intracellular and extracellular proteases showed the strongest activity under acidic conditions, which were considered suitable for cheese application. The raw culture product (CP) and its freeze-dried product (FDP) were mixed with cheese curds, prepared according to Gouda-type cheese-making methods, and were allowed to ripen for 3 months. Chemical analysis of the products showed 13.3% water-soluble nitrogen (WSN) in the control, which had received noncultured media, whereas 20.0% and 21.1% WSN was found in the CP and FDP experimental cheeses, respectively. Although these adjuncts significantly increased WSN, an insignificant difference was found between CP and FDP. Free fatty acids in all experimental cheeses were similar, showing that CP and FDP caused no rancid defects.

CONCLUSION

The introduction of freeze-drying treatments accompanied by cell disruption resulted in a negligible effect in terms of WSN. However, the application of A. sojae can be beneficial when it comes to increasing the level of WSN compared with A. oryzae, as shown in our previous study. © 2020 Society of Chemical Industry.

Invasive growth of Aspergillus oryzae in rice koji and increase of nuclear number

BACKGROUND

'Rice koji' is a solid culture of Aspergillus oryzae on steamed rice grains. Multiple parallel fermentation, wherein saccharification of rice by A. oryzae and alcohol fermentation by the budding yeast occur simultaneously, leads to the formation of a variety of ingredients of Japanese sake. In sake brewing, the degree of mycelial invasive growth into the steamed rice, called 'haze-komi', highly correlates with the digestibility and quality of rice koji, since the hyphae growing into the rice secrete amylases and digest starch.

RESULTS

In this study, we investigated mycelial distribution of GFP-tagged A. oryzae in rice koji made with different types of rice, such as sake rice and eating rice, with 50 or 90% polishing rate to remove abundant proteins and lipids near the surface. In addition, we compared transcriptomes of A. oryzae in the different types of rice koji. Finally, we found that A. oryzae increases the nuclear number and hyphal width in the course of 1-3 days cultivation.

CONCLUSIONS

Our imaging analyses indicate that A. oryzae hyphae grew more deeply into 50% polished rice than 90% polished rice. The increases of nuclear number may be a selectively acquired characteristic for the high secretory capacity during the long history of cultivation of this species.

Regulatory mechanisms for amylolytic gene expression in the koji mold Aspergillus oryzae

The koji mold Aspergillus oryzae has been used in traditional Japanese food and beverage fermentation for over a thousand years. Amylolytic enzymes are important in sake fermentation, wherein production is induced by starch or malto-oligosaccharides. This inducible production requires at least two transcription activators, AmyR and MalR. Among amylolytic enzymes, glucoamylase GlaB is produced exclusively in solid-state culture and plays a critical role in sake fermentation owing to its contribution to glucose generation from starch. A recent study demonstrated that glaB gene expression is regulated by a novel transcription factor, FlbC, in addition to AmyR in solid-state culture. Amylolytic enzyme production is generally repressed by glucose due to carbon catabolite repression (CCR), which is mediated by the transcription factor CreA. Modifying CCR machinery, including CreA, can improve amylolytic enzyme production. This review focuses on the role of transcription factors in regulating A. oryzae amylolytic gene expression.

Understanding the regulation of extracellular protease gene expression in fungi: a key step towards their biotechnological applications

The secretion of proteases by certain species of yeast and filamentous fungi is of importance not only for their biological function and survival, but also for their biotechnological application to various processes in the food, beverage, and bioprocessing industries. A key step towards understanding the role that these organisms play in their environment, and how their protease-secreting ability may be optimally utilised through industrial applications, involves an evaluation of those factors which influence protease production. The objective of this review is to provide an overview of the findings from investigations directed at elucidating the regulatory mechanisms underlying extracellular protease secretion in yeast and filamentous fungi, and the environmental stimuli that elicit these responses. The influence of nitrogen-, carbon-, and sulphur-containing compounds, as well as proteins, temperature, and pH, on extracellular protease regulation, which is frequently exerted at the transcriptional level, is discussed in particular depth. Protease-secreting organisms of biotechnological interest are also presented in this context, in an effort to explore the areas of industrial significance that could possibly benefit from such knowledge. In this way, the establishment of a platform of existing knowledge regarding fungal protease regulation is attempted, with the particular goal of aiding in the practical application of these organisms to processes that require secretion of this enzyme.

Extracellular Proteome Analysis and Flavor Formation During Soy Sauce Fermentation

Aspergillus oryzae is an excellent strain for soy sauce fermentation because of its complicated enzyme system, especially protease. The aim of this study was to investigate the key enzymes and flavors during soy sauce fermentation, and a comparative assessment of extracellular enzymes during various fermentation stages at the proteomic level via iTRAQ analysis is presented. Many important enzymes related to the amino acid and glucose metabolisms participated in the material decomposition under high-salt stress. Dipeptidase, dipeptidyl aminopeptidase, leucine aminopeptidase, aspartic protease pep1, and extracellular metalloproteinase played positive roles during the early stage of soybean mash fermentation, whilst leucine aminopeptidase A and extracellular metalloproteinase NpI were the dominant proteolytic enzymes during the later period of fermentation. At the same time, β-glucosidase and β-xylanase exerted great effects upon glucose metabolism throughout the fermentation process. The results show that protease and amylolytic enzymes are complementary in the formation of flavors such as alcohols, acids, esters, aldehydes, furans, and pyrazines during soy sauce fermentation.

Agmatine Production by Aspergillus oryzae Is Elevated by Low pH during Solid-State Cultivation

Sake (rice wine) produced by multiple parallel fermentation (MPF) involving Aspergillus oryzae (strain RW) and Saccharomyces cerevisiae under solid-state cultivation conditions contained 3.5 mM agmatine, while that produced from enzymatically saccharified rice syrup by S. cerevisiae contained <0.01 mM agmatine. Agmatine was also produced in ethanol-free rice syrup prepared with A. oryzae under solid-state cultivation (3.1 mM) but not under submerged cultivation, demonstrating that A. oryzae in solid-state culture produces agmatine. The effect of cultivation conditions on agmatine production was examined. Agmatine production was boosted at 30°C and reached the highest level (6.3 mM) at pH 5.3. The addition of l-lactic, succinic, and citric acids reduced the initial culture pHs to 3.0, 3.5, and 3.2, respectively, resulting in a further increase in agmatine accumulation (8.2, 8.7, and 8.3 mM, respectively). Homogenate from a solid-state culture exhibited a maximum l-arginine decarboxylase (ADC) activity (74 pmol · min^-1 · μg^-1) at pH 3.0 at 30°C; homogenate from a submerged culture exhibited an extremely low activity (<0.3 pmol · min^-1 · μg^-1) under all conditions tested. These observations indicated that efficient agmatine production in ethanol-free rice syrup is achieved by an unidentified low-pH-dependent ADC induced during solid-state cultivation of A. oryzae, even though A. oryzae lacks ADC orthologs and instead possesses four ornithine decarboxylases (ODC1 to ODC4). Recombinant ODC1 and ODC2 exhibited no ADC activity at acidic pH (pH < 4.0), suggesting that other decarboxylases or an unidentified ADC is involved in agmatine production.IMPORTANCE It has been speculated that, in general, fungi do not synthesize agmatine from l-arginine because they do not possess genes encoding arginine decarboxylase. Numerous preclinical studies have shown that agmatine exerts pleiotropic effects on various molecular targets, leading to an improved quality of life. In the present study, we first demonstrated that l-arginine was a feasible substrate for agmatine production by the fungus Aspergillus oryzae RW. We observed that the productivity of agmatine by A. oryzae RW was elevated at low pH only during solid-state cultivation. A. oryzae is utilized in the production of various Asian fermented foods. The saccharification conditions optimized in the current study could be employed not only in the production of an agmatine-containing ethanol-free rice syrup but also in the production of many types of fermented foods, such as soy sauce (shoyu), rice vinegar, etc., as well as for use as novel therapeutic agents and nutraceuticals.

Quantitative evaluation of haze formation of koji and progression of internal haze by drying of koji during koji making

The construction of an experimental system that can mimic koji making in the manufacturing setting of a sake brewery is initially required for the quantitative evaluation of mycelia grown on/in koji pellets (haze formation). Koji making with rice was investigated with a solid-state fermentation (SSF) system using a non-airflow box (NAB), which produced uniform conditions in the culture substrate with high reproducibility and allowed for the control of favorable conditions in the substrate during culture. The SSF system using NAB accurately reproduced koji making in a manufacturing setting. To evaluate haze formation during koji making, surfaces and cross sections of koji pellets obtained from koji making tests were observed using a digital microscope. Image analysis was used to distinguish between haze and non-haze sections of koji pellets, enabling the evaluation of haze formation in a batch by measuring the haze rate of a specific number of koji pellets. This method allowed us to obtain continuous and quantitative data on the time course of haze formation. Moreover, drying koji during the late stage of koji making was revealed to cause further penetration of mycelia into koji pellets (internal haze). The koji making test with the SSF system using NAB and quantitative evaluation of haze formation in a batch by image analysis is a useful method for understanding the relations between haze formation and koji making conditions.

Whole-genome de novo sequencing, combined with RNA-Seq analysis, reveals unique genome and physiological features of the amylolytic yeast Saccharomycopsis fibuligera and its interspecies hybrid

BACKGROUND

Genomic studies on fungal species with hydrolytic activity have gained increased attention due to their great biotechnological potential for biomass-based biofuel production. The amylolytic yeast Saccharomycopsis fibuligera has served as a good source of enzymes and genes involved in saccharification. Despite its long history of use in food fermentation and bioethanol production, very little is known about the basic physiology and genomic features of S. fibuligera.

RESULTS

We performed whole-genome (WG) de novo sequencing and complete assembly of S. fibuligera KJJ81 and KPH12, two isolates from wheat-based Nuruk in Korea. Intriguingly, the KJJ81 genome (~38 Mb) was revealed as a hybrid between the KPH12 genome (~18 Mb) and another unidentified genome sharing 88.1% nucleotide identity with the KPH12 genome. The seven chromosome pairs of KJJ81 subgenomes exhibit highly conserved synteny, indicating a very recent hybridization event. The phylogeny inferred from WG comparisons showed an early divergence of S. fibuligera before the separation of the CTG and Saccharomycetaceae clades in the subphylum Saccharomycotina. Reconstructed carbon and sulfur metabolic pathways, coupled with RNA-Seq analysis, suggested a marginal Crabtree effect under high glucose and activation of sulfur metabolism toward methionine biosynthesis under sulfur limitation in this yeast. Notably, the lack of sulfate assimilation genes in the S. fibuligera genome reflects a unique phenotype for Saccharomycopsis clades as natural sulfur auxotrophs. Extended gene families, including novel genes involved in saccharification and proteolysis, were identified. Moreover, comparative genome analysis of S. fibuligera ATCC 36309, an isolate from chalky rye bread in Germany, revealed that an interchromosomal translocation occurred in the KPH12 genome before the generation of the KJJ81 hybrid genome.

CONCLUSIONS

The completely sequenced S. fibuligera genome with high-quality annotation and RNA-Seq analysis establishes an important foundation for functional inference of S. fibuligera in the degradation of fermentation mash. The gene inventory facilitates the discovery of new genes applicable to the production of novel valuable enzymes and chemicals. Moreover, as the first gapless genome assembly in the genus Saccharomycopsis including members with desirable traits for bioconversion, the unique genomic features of S. fibuligera and its hybrid will provide in-depth insights into fungal genome dynamics as evolutionary adaptation.

The C2H2-type transcription factor, FlbC, is involved in the transcriptional regulation of Aspergillus oryzae glucoamylase and protease genes specifically expressed in solid-state culture

Aspergillus oryzae produces a large amount of secreted proteins in solid-state culture, and some proteins such as glucoamylase (GlaB) and acid protease (PepA) are specifically produced in solid-state culture, but rarely in submerged culture. From the disruption mutant library of A. oryzae transcriptional regulators, we successfully identified a disruption mutant showing an extremely low production level of GlaB but a normal level of α-amylase production. This strain was a disruption mutant of the C2H2-type transcription factor, FlbC, which is reported to be involved in the regulation of conidiospore development. Disruption mutants of other upstream regulators comprising a conidiation regulatory network had no apparent effect on GlaB production in solid-state culture. In addition to GlaB, the production of acid protease in solid-state culture was also markedly decreased by flbC disruption. Northern blot analyses revealed that transcripts of glaB and pepA were significantly decreased in the flbC disruption strain. These results suggested that FlbC is involved in the transcriptional regulation of genes specifically expressed under solid-state cultivation conditions, possibly independent of the conidiation regulatory network.

Different Polar Metabolites and Protein Profiles between High- and Low-Quality Japanese Ginjo Sake

Japanese ginjo sake is a premium refined sake characterized by a pleasant fruity apple-like flavor and a sophisticated taste. Because of technical difficulties inherent in brewing ginjo sake, off-flavors sometimes occur. However, the metabolites responsible for off-flavors as well as those present or absent in higher quality ginjo sake remain uncertain. Here, the relationship between 202 polar chemical compounds in sake identified using capillary electrophoresis coupled with time-of-flight mass spectrometry and its organoleptic properties, such as quality and off-flavor, was examined. First, we found that some off-flavored sakes contained higher total amounts of metabolites than other sake samples. The results also identified that levels of 2-oxoglutaric acid and fumaric acid, metabolites in the tricarboxylic acid cycle, were highly but oppositely correlated with ginjo sake quality. Similarly, pyridoxine and pyridoxamine, co-enzymes for amino transferase, were also highly but oppositely correlated with ginjo sake quality. Additionally, pyruvic acid levels were associated with good quality as well. Compounds involved in the methionine salvage cycle, oxidative glutathione derivatives, and amino acid catabolites were correlated with low quality. Among off-flavors, an inharmonious bitter taste appeared attributable to polyamines. Furthermore, protein analysis displayed that a diversity of protein components and yeast protein (triosephosphate isomerase, TPI) leakage was linked to the overall metabolite intensity in ginjo sake. This research provides insight into the relationship between sake components and organoleptic properties.

Purification and characterization of the extracellular aspartyl protease APSm1 from the phytopathogen fungus Stenocarpella maydis

The extracellular protease APSm1 was purified to homogeneity from Stenocarpella maydis that was grown in acidic minimal media with glucose and ammonium sulfate. The purification procedure consisted of ion exchange chromatography coupled to an FPLC (Fast Protein Liquid Chromatography) system, resulting in a 15.3% recovery and a 2.3-fold increase in specific activity. The molecular weight of the purified enzyme was estimated to be 56.8 kDa by SDS-PAGE. Enzymatic activity toward hemoglobin was optimal at pH 2.0 and at 25 °C. The effects of six protease inhibitors on APSm1 activity were tested. Pepstatin A inhibited APSm1 activity, as the protein is in fact an aspartyl protease. The pure enzyme degraded hemoglobin, albumin and proteins obtained from corn germ at pH 3 but did not have any milk-clotting activities. The Km and Vmax values obtained were 0.514 mg/mL and 0.222 μmol/min, respectively, using hemoglobin as the substrate. This work is the first to report the purification of a secreted aspartyl protease from S. maydis.

Identification of pyroglutamyl peptides in Japanese rice wine (sake): presence of hepatoprotective pyroGlu-Leu

Japanese rice wine, sake, is made from steamed rice, water, and lactic acid by "multiple parallel fermentation" with mold (Aspergillus oryzae) and yeast (Saccharomyces cerevisiae). Nineteen pyroglutamyl peptides were identified in commercially available sake. Among them, pyroGlu-Leu and pyroGlu-Gln were the major constituents. PyroGlu-Leu has been demonstrated to attenuate hepatitis and colitis in animal models. Commercial products (n = 5) contained pyroGlu-Leu at concentrations ranging from 40 to 60 μM (10-15 mg/L). The pyroGlu-Leu content in sake mash increased during the fermentation processes. However, no pyroGlu-Leu was produced by yeast inoculated into preheated mash. Furthermore, addition of (13)C-Leu to the mash did not increase the ratio of pyroGlu-(13)C-Leu to pyroGlu-(12)C-Leu. On the other hand, digestion of steamed rice with A. oryzae proteases increased the pyroGlu-Leu content. These results indicate that pyroGlu-Leu in sake is produced from rice proteins by digestion with A. oryzae proteases.

Comparative study on the properties of lipopeptide products and expression of biosynthetic genes from Bacillus amyloliquefaciens XZ-173 in liquid fermentation and solid-state fermentation

This study compared the compositions and properties of lipopeptide products purified from liquid fermentation (LF) and solid-state fermentation (SSF) and transcription levels involved in lipopeptides under the two systems. Results of Fourier transform infrared spectroscopy and High performance liquid chromatography revealed no significant differences in the polarity and structure of the two lipopeptide products. A higher amino acid proportion was found for lipopeptide product in LF than in SSF. Lipopeptide product produced from LF had better emulsification and antagonistic activities than that from SSF. For SSF, the transcription accumulation levels of the lipopeptide synthetic genes srfAA and sfp were higher than for LF at the same stage. Transcripts for ituD and lpa-14 remained elevated for a longer period of time under SSF conditions, accounting for differences in the production and fermentation periods between SSF and LF. This is the first report that describes differences in lipopeptide product synthesis and molecular behaviors between LF and SSF systems.

Biochemical study of the extracellular aspartyl protease Eap1 from the phytopathogen fungus Sporisorium reilianum

In this work, the extracellular protease Eap1 from Sporisorium reilianum was characterized in solid and liquid cultures using different culture media. The results showed that Eap1 was produced in all media and under all culture conditions, with the most activity in solid culture at an acidic pH of 3-5. Following purification, the 41 kDa protease demonstrated aspartyl protease activity. The enzyme was stable at a wide range of temperatures and pH values, but 45°C and pH 3 were optimal. The K(m) and V(max( values obtained were 0.69 mg/mL and 0.66 μmol/min, respectively, with albumin as the substrate. Eap1 degraded hemoglobin as well as proteins obtained from corn germ, roots, stems and slides at pH 3 and also had milk-clotting activity. Sequencing analysis showed that this protein has 100% similarity to the peptide sequence theoretically obtained from the sr11394 gene, which encodes an aspartyl protease secreted by S. reilianum.

Comparative Analysis of Aspergillus oryzae with Normal and Abnormal Color Conidia

This study focuses on the characteristic of strains with anomalous color conidium and compares with normal color conidium. Comparative analysis of enzymes activity and extracellular proteins revealed that A. oryzae with anomalous color conidium was not different from the strain with normal color conidium. In addition, A. oryzae with anomalous color conidium could not influence the palatability and quality of the soy sauce. These findings provide an insight into A. oryzae with anomalous color conidium.

Characterisation of acid proteases from a fusant F76 and its progenitors Aspergillus oryzae HN3042 and Aspergillus niger CICC2377

The characteristics of a novel acid protease from a fusant F76 were comparatively evaluated with those from its progenitors Aspergillus oryzae HN3042 and A. niger CICC2377. The UV spectra of these three acid proteases were similar, but fluorescence spectra were different. The acid protease from F76 contained 7.1% α‐helix, 39.4% β‐sheet, 24.7% β‐turn and 32% aperiodic coil, unlike those from its progenitors. The acid protease from F76 was active in the temperature range of 35–55 °C with the optimum temperature of 40 °C and was stable in the pH range of 2.5–6.5 with the optimum pH of 3.5, while those values from A. oryzae HN3042 and A. niger CICC2377 were 45 °C, 4.0 and 40 °C, 3.5, respectively. The kinetic parameters of the acid protease from F76 were different from its progenitors and the Michaelis constant, maximum velocity, activation energy, and attenuation index were 0.96 mg mL−1, 135.14 μmol min−1 mg−1, 64.11 kJ mol−1 and 0.59, respectively.

Identification of regulatory elements in the glucoamylase-encoding gene (glaB) promoter from Aspergillus oryzae

The Aspergillus oryzae glucoamylase-encoding gene glaB is expressed specifically and strongly only during solid-state cultivation (SSC). To elucidate the basis for the specificity, the glaB promoter was analyzed by electrophoretic gel mobility shift assay (EMSA) which indicated two protein-binding elements from -382 to -353 and from -332 to -313. To confirm that these regions contained cis-elements, deletion analysis of the promoter was undertaken using β-glucuronidase as a reporter. The results of the deletion analysis were consistent with the EMSA results. The promoter missing the -332 to -313 element was not induced by low water activity stress during SSC.

Pepsin-like aspartic protease (Sc-ASP155) cloning, molecular characterization and gene expression analysis in developmental stages of nematode Steinernema carpocapsae

Steinernema carpocapsae is an insect parasitic nematode associated with the bacterium Xenorhabdus nematophila. These symbiotic complexes are virulent against the insect host. Many protease genes were shown previously to be induced during parasitism, including one predicted to encode an aspartic protease, which was cloned and analyzed in this study. A cDNA encoding Sc-ASP155 was cloned based on the EST fragment. The full-length cDNA of Sc-ASP155 consists of 955 nucleotides with multiple domains, including a signal peptide (aa1-15), a pro-peptide region (aa16-45), and a typical catalytic aspartic domain (aa71-230). The putative 230 amino acid residues have a calculated molecular mass of 23,812Da and a theoretical pI of 5.01. Sc-ASP155 blastp analysis showed 40-62% amino acid sequence identity to aspartic proteases from parasitic and free-living nematodes. Expression analysis showed that the sc-asp155 gene was up-regulated during the initial parasitic stage, especially in L3 gut and 6h induced nematodes. Sequence comparison revealed that Sc-ASP155 was a member of an aspartic protease family and phylogenetic analysis indicated that Sc-ASP155 was clustered with Sc-ASP113. In situ hybridization showed that sc-asp155 was expressed in subventral cells. Additionally, we determined that sc-asp155 is a single-copy gene in S. carpocapsae. Homology modeling showed that Sc-ASP155 adopts a typical aspartic protease structure. The up-regulated Sc-ASP155 expression revealed that this protease could play a role in the parasitic process. In this study, we have cloned the gene and determined the expression of the pepsin-like aspartic protease Sc-ASP155 in S. carpocapsae.