Regulation of the glucoamylase-encoding gene (glaB), expressed in solid-state culture (koji) of Aspergillus oryzae

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.

Expression of heterochromatin protein 1 affects citric acid production in Aspergillus luchuensis mut. kawachii

A putative methyltransferase, LaeA, controls citric acid production through epigenetic regulation of the citrate exporter gene, cexA, in the white koji fungus Aspergillus luchuensis mut. kawachii. In this study, we investigated the role of another epigenetic regulator, heterochromatin protein 1, HepA, in citric acid production. The ΔhepA strain exhibited reduced citric acid production in liquid culture, although to a lesser extent compared to the ΔlaeA strain. In addition, the ΔlaeA ΔhepA strain showed citric acid production similar to the ΔlaeA strain, indicating that HepA plays a role in citric acid production, albeit with a less-significant regulatory effect than LaeA. RNA-seq analysis revealed that the transcriptomic profiles of the ΔhepA and ΔlaeA strains were similar, and the expression level of cexA was reduced in both strains. These findings suggest that the genes regulated by HepA are similar to those regulated by LaeA in A. luchuensis mut. kawachii. However, the reductions in citric acid production and cexA expression observed in the disruptants were mitigated in rice koji, a solid-state culture. Thus, the mechanism by which citric acid production is regulated differs between liquid and solid cultivation. Further investigation is thus needed to understand the regulatory mechanism in koji.

Laccase Activity in Fungus Cryphonectria parasitica Is Affected by Growth Conditions and Fungal-Viral Genotypic Interactions

Laccase activity reduction in the chestnut blight fungus Cryphonectria parasitica usually accompanies the hypovirulence caused by the infection of fungus with Cryphonectria hypovirus 1 (CHV1). However, the different methods utilized for assessing this phenomenon has produced varied and often conflicting results. Furthermore, the majority of experimental setups included only one prototypic system, further confounding the results. Considering the diversity of fungal isolates, viral strains, and variability of their effects on the phytopathogenic process observed in nature, our goal was to ascertain if laccase activity variability is affected by (1) different C. parasitica isolates infected with several CHV1 strains, and (2) growth conditions. We have demonstrated that some CHV1 strains, contrary to previous assumptions, increase the activity of C. parasitica laccases. The specific fungal isolates used in the experiments and culture conditions also affected the results. Furthermore, we showed that two commonly used laccase substrates, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) and 2,4-dimethoxyphenol, cannot be used interchangeably in C. parasitica laccase activity measurements. Our results illustrate the importance of conducting this type of study in experimental systems and culture conditions that resemble natural conditions as much as possible to be able to infer the most relevant conclusions applicable to natural populations.

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.

Making Traditional Japanese Distilled Liquor, Shochu and Awamori, and the Contribution of White and Black Koji Fungi

The traditional Japanese single distilled liquor, which uses koji and yeast with designated ingredients, is called "honkaku shochu." It is made using local agricultural products and has several types, including barley shochu, sweet potato shochu, rice shochu, and buckwheat shochu. In the case of honkaku shochu, black koji fungus (Aspergillus luchuensis) or white koji fungus (Aspergillus luchuensis mut. kawachii) is used to (1) saccharify the starch contained in the ingredients, (2) produce citric acid to prevent microbial spoilage, and (3) give the liquor its unique flavor. In order to make delicious shochu, when cultivating koji fungus during the shochu production process, we use a unique temperature control method to ensure that these three important elements, which greatly affect the taste of the produced liquor, are balanced without any excess or deficiency. This review describes in detail the production method of honkaku shochu, a distilled spirit unique to Japan and whose market is expected to expand worldwide, with special attention paid to the koji fungi cultivation step. Furthermore, we describe the history of the koji fungi used today in the production of shochu, and we provide a thorough explanation of the characteristics of each koji fungi. We also report the latest research progress on this topic.

Expression profiles of amylolytic genes in AmyR and CreA transcription factor deletion mutants of the black koji mold Aspergillus luchuensis

The black koji mold, Aspergillus luchuensis, which belongs to Aspergillus section Nigri, is used for the production of traditional Japanese spirits (shochu) mainly in the southern districts of Japan. This mold is known to produce amylolytic enzymes essential for shochu production; however, mechanisms regulating amylolytic gene expression in A. luchuensis have not been studied in as much detail as those in the yellow koji mold, Aspergillus oryzae. Here, we examined the gene expression profiles of deletion mutants of transcription factors orthologous to A. oryzae AmyR and CreA in A. luchuensis. A. luchuensis produces acid-unstable (AmyA) and acid-stable (AsaA) α-amylases. AmyA production and amyA gene expression were not influenced by amyR or creA deletion, indicating that amyA was constitutively expressed. In contrast, asaA gene expression was significantly down- and upregulated upon deletion of amyR and creA, respectively. Furthermore, the glaA and agdA genes (encoding glucoamylase and α-glucosidase, respectively) showed expression profiles similar to those of asaA. Thus, genes that play pivotal roles in starch saccharification, asaA, glaA, and agdA, were found to be regulated by AmyR and CreA. Moreover, despite previous reports on AsaA being only produced in solid-state culture, deletion of the ortholog of A. oryzae flbC, which is involved in the expression of the solid-state culture-specific genes, did not affect AsaA α-amylase activity, suggesting that FlbC was not associated with asaA expression.

Induction and Repression of Hydrolase Genes in Aspergillus oryzae

The filamentous fungus Aspergillus oryzae, also known as yellow koji mold, produces high levels of hydrolases such as amylolytic and proteolytic enzymes. This property of producing large amounts of hydrolases is one of the reasons why A. oryzae has been used in the production of traditional Japanese fermented foods and beverages. A wide variety of hydrolases produced by A. oryzae have been used in the food industry. The expression of hydrolase genes is induced by the presence of certain substrates, and various transcription factors that regulate such expression have been identified. In contrast, in the presence of glucose, the expression of the glycosyl hydrolase gene is generally repressed by carbon catabolite repression (CCR), which is mediated by the transcription factor CreA and ubiquitination/deubiquitination factors. In this review, we present the current knowledge on the regulation of hydrolase gene expression, including CCR, in A. oryzae.

The Anaerobic Fungi: Challenges and Opportunities for Industrial Lignocellulosic Biofuel Production

Lignocellulose is a promising feedstock for biofuel production as a renewable, carbohydrate-rich and globally abundant source of biomass. However, challenges faced include environmental and/or financial costs associated with typical lignocellulose pretreatments needed to overcome the natural recalcitrance of the material before conversion to biofuel. Anaerobic fungi are a group of underexplored microorganisms belonging to the early diverging phylum Neocallimastigomycota and are native to the intricately evolved digestive system of mammalian herbivores. Anaerobic fungi have promising potential for application in biofuel production processes due to the combination of their highly effective ability to hydrolyse lignocellulose and capability to convert this substrate to H2 and ethanol. Furthermore, they can produce volatile fatty acid precursors for subsequent biological conversion to H2 or CH4 by other microorganisms. The complex biological characteristics of their natural habitat are described, and these features are contextualised towards the development of suitable industrial systems for in vitro growth. Moreover, progress towards achieving that goal is reviewed in terms of process and genetic engineering. In addition, emerging opportunities are presented for the use of anaerobic fungi for lignocellulose pretreatment; dark fermentation; bioethanol production; and the potential for integration with methanogenesis, microbial electrolysis cells and photofermentation.

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.

Environmental cues that induce the physiology of solid medium: a study on lovastatin production by Aspergillus terreus

AIMS

The aim of this work was to identify the main environmental factors that induce the special physiology displayed by fungi growing in solid culture-that is, higher secondary metabolite (SM) production-compared with those in submerged culture.

METHODS AND RESULTS

Lovastatin-specific production (SP) was used as an indicator of the physiological status, and different model culture systems were used to evaluate the impact of potential solid-state fermentation (SSF) environmental stimuli. Direct contact with air was identified as an important stimulus. Cultures with two or more hours of exposure to air showed typical SSF lovastatin SP (1462% higher than cultures exposed for 0·08 h). Intermediate times of exposure generated intermediate physiological states. Support-related stimuli also induced higher lovastatin SP, even in a liquid environment (679% increase).

CONCLUSIONS

Direct contact with air, as well as support-related stimuli, are major environmental cues that induce the physiology of solid medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

This knowledge is the starting point to investigate how these environmental cues are sensed and transduced, impacting SM and enzyme production. These results have important applied potential in new strategies to generate overproducing strains, as well as application in the design of novel production systems.

Genome sequence of Aspergillus luchuensis NBRC 4314

Awamori is a traditional distilled beverage made from steamed Thai-Indica rice in Okinawa, Japan. For brewing the liquor, two microbes, local kuro (black) koji mold Aspergillus luchuensis and awamori yeast Saccharomyces cerevisiae are involved. In contrast, that yeasts are used for ethanol fermentation throughout the world, a characteristic of Japanese fermentation industries is the use of Aspergillus molds as a source of enzymes for the maceration and saccharification of raw materials. Here we report the draft genome of a kuro (black) koji mold, A. luchuensis NBRC 4314 (RIB 2604). The total length of nonredundant sequences was nearly 34.7 Mb, comprising approximately 2,300 contigs with 16 telomere-like sequences. In total, 11,691 genes were predicted to encode proteins. Most of the housekeeping genes, such as transcription factors and N-and O-glycosylation system, were conserved with respect to Aspergillus niger and Aspergillus oryzae An alternative oxidase and acid-stable α-amylase regarding citric acid production and fermentation at a low pH as well as a unique glutamic peptidase were also found in the genome. Furthermore, key biosynthetic gene clusters of ochratoxin A and fumonisin B were absent when compared with A. niger genome, showing the safety of A. luchuensis for food and beverage production. This genome information will facilitate not only comparative genomics with industrial kuro-koji molds, but also molecular breeding of the molds in improvements of awamori fermentation.

A novel non-thermostable deuterolysin from Aspergillus oryzae

Three putative deuterolysin (EC 3.4.24.29) genes (deuA, deuB, and deuC) were found in the Aspergillus oryzae genome database ( http://www.bio.nite.go.jp/dogan/project/view/AO ). One of these genes, deuA, was corresponding to NpII gene, previously reported. DeuA and DeuB were overexpressed by recombinant A. oryzae and were purified. The degradation profiles against protein substrates of both enzymes were similar, but DeuB showed wider substrate specificity against peptidyl MCA-substrates compared with DeuA. Enzymatic profiles of DeuB except for thermostability also resembled those of DeuA. DeuB was inactivated by heat treatment above 80° C, different from thermostable DeuA. Transcription analysis in wild type A. oryzae showed only deuB was expressed in liquid culture, and the addition of the proteinous substrate upregulated the transcription. Furthermore, the NaNO3 addition seems to eliminate the effect of proteinous substrate for the transcription of deuB.

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.

A fungal biofilm reactor based on metal structured packing improves the quality of a Gla::GFP fusion protein produced by Aspergillus oryzae

Fungal biofilm is known to promote the excretion of secondary metabolites in accordance with solid-state-related physiological mechanisms. This work is based on the comparative analysis of classical submerged fermentation with a fungal biofilm reactor for the production of a Gla::green fluorescent protein (GFP) fusion protein by Aspergillus oryzae. The biofilm reactor comprises a metal structured packing allowing the attachment of the fungal biomass. Since the production of the target protein is under the control of the promoter glaB, specifically induced in solid-state fermentation, the biofilm mode of culture is expected to enhance the global productivity. Although production of the target protein was enhanced by using the biofilm mode of culture, we also found that fusion protein production is also significant when the submerged mode of culture is used. This result is related to high shear stress leading to biomass autolysis and leakage of intracellular fusion protein into the extracellular medium. Moreover, 2-D gel electrophoresis highlights the preservation of fusion protein integrity produced in biofilm conditions. Two fungal biofilm reactor designs were then investigated further, i.e. with full immersion of the packing or with medium recirculation on the packing, and the scale-up potentialities were evaluated. In this context, it has been shown that full immersion of the metal packing in the liquid medium during cultivation allows for a uniform colonization of the packing by the fungal biomass and leads to a better quality of the fusion protein.

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.

The influence of inoculum composition on selected bioactive and nutritional parameters of grass pea tempeh obtained by mixed-culture fermentation with Rhizopus oligosporus and Aspergillus oryzae strains

Tempeh is a popular Indonesian product obtained from legume seeds by solid-state fermentation with Rhizopus sp. The aim of this research was to study the effect of simultaneous mixed-culture fermentation of grass pea seeds on selected parameters of products as compared to traditional tempeh. The inoculum contained different ratios of Rhizopus oligosporus and Aspergillus oryzae spores. The simultaneous fermentation of grass pea seeds with inoculum consisting of 1.2 × 10(6) R. oligosporus and 0.6 × 10(6) A. oryzae spores (per 60 g of seeds) resulted in a product of improved quality, as compared with traditionally made tempeh (obtained after inoculation with 1.2 × 10(6) R. oligosporus spores), at the same fermentation time. This product had radical scavenging ability 70% higher than the one obtained with pure R. oligosporus culture and contained 2.23 g/kg dm of soluble phenols. The thiamin and riboflavin levels were above three (340 µg/g dm) and two (50.50 µg/g dm) folds higher than in traditionally made tempeh, respectively. The product had 65% in vitro bioavailability of proteins and 33% in vitro bioavailability of sugars. It also contained 40% less 3-N-oxalyl-L-2, 3-diaminopropionic acid (0.074 g/kg dm), as compared to traditional tempeh.

Production of Pectate Lyase by Penicillium viridicatum RFC3 in Solid-State and Submerged Fermentation

Pectate lyase (PL) was produced by the filamentous fungus Penicillium viridicatum RFC3 in solid-state cultures of a mixture of orange bagasse and wheat bran (1 : 1 w/w), or orange bagasse, wheat bran and sugarcane bagasse (1 : 1 : 0.5 w/w), and in a submerged liquid culture with orange bagasse and wheat bran (3%) as the carbon source. PL production was highest (1,500 U mL(-1) or 300 Ug(-1) of substrate) in solid-state fermentation (SSF) on wheat bran and orange bagasse at 96 hours. PL production in submerged fermentation (SmF) was influenced by the initial pH of the medium. With the initial pH adjusted to 4.5, 5.0, and 5.5, the peak activity was observed after 72, 48, and 24 hours of fermentation, respectively, when the pH of the medium reached the value 5.0. PL from SSF and SmF were loaded on Sephadex-G75 columns and six activity peaks were obtained from crude enzyme from SSF and designated PL I, II, III, IV, V, and VI, while five peaks were obtained from crude enzyme from SmF and labeled PL I', II', III', IV', and VII'. Crude enzyme and fraction III from each fermentative process were tested further. The optimum pH for crude PL from either process was 5.5, while that for PL III was 8.0. The maximum activity of enzymes from SSF was observed at 35 degrees C, but crude enzyme was more thermotolerant than PL III, maintaining its maximum activity up to 45 degrees C. Crude enzyme from SmF and PL III' showed thermophilic profiles of activity, with maximum activity at 60 and 55 degrees C, respectively. In the absence of substrate, the crude enzyme from SSF was stable over the pH range 3.0-10.0 and PL III was most stable in the pH range 4.0-7.0. Crude enzyme from SmF retained 70%-80% of its maximum activity in the acid-neutral pH range (4.0-7.0), but PIII showed high stability at alkaline pH (7.5-9.5). PL from SSF was more thermolabile than that from SmF. The latter maintained 60% of its initial activity after 1 h at 55 degrees C. The differing behavior of the enzymes with respect to pH and temperature suggests that they are different isozymes.

Regulation of environmental factors on the expression of a solid-state specific lipase (Lip1) with Rhizopus chinensis by western blot and indirect Elisa

To identify which solid-state typical environmental factors are involved in the induction of a solid-state special lipase (Lip1), western blot and Elisa based on Lip1 antibody were used. A low water activity played a significant role in the induction of Lip1, as evidenced by the increased expression level (20-46 microg/g dry cell) along with the decrease of water activity (0.927-0.969). Physical barrier against hyphal extension was found to be another required factor, since the expression of Lip1 was significantly enhanced by 3-fold using a membrane with smaller pore size (0.45 and 0.22 microm) covered on top of surface culture.

Solid state fermentation of lipopeptide antibiotic iturin A by using a novel solid state fermentation reactor system

A new solid state fermentation reactor (SSFR) for solid substrate was used for the production of lipopeptide antibiotic iturin A using Bacillus subtilis RB14-CS. Solid state fermentation (SSF) is the technique of cultivation of microorganisms on solid and moist substrates in the absence of free water. SSF has shown much promise in the development of several bioprocesses and products because of their several advantages like absence of free water that allows simplified downstream processing and low cost. SSFR allows agitation of the SSF culture with improved temperature control and air supply. Interestingly, when okara, the widely available waste product from the tofu industries, was used as the solid substrate for the SSFR, no iturin A production was observed. However, without agitation, production of iturin A was observed in the SSFR but the production level remained low. The low production of iturin A was found to be due to the heat generation and excess temperature rise inside the reactor system during the fermentation process. Maintaining the temperature within a range of 25-30°C, production of iturin A was significantly improved in the SSFR. This was comparable to the laboratory scale production, and signifies the potential application of the SSFR for SSF.

Filamentous fungi for production of food additives and processing aids

Filamentous fungi are metabolically versatile organisms with a very wide distribution in nature. They exist in association with other species, e.g. as lichens or mycorrhiza, as pathogens of animals and plants or as free-living species. Many are regarded as nature's primary degraders because they secrete a wide variety of hydrolytic enzymes that degrade waste organic materials. Many species produce secondary metabolites such as polyketides or peptides and an increasing range of fungal species is exploited commercially as sources of enzymes and metabolites for food or pharmaceutical applications. The recent availability of fungal genome sequences has provided a major opportunity to explore and further exploit fungi as sources of enzymes and metabolites. In this review chapter we focus on the use of fungi in the production of food additives but take a largely pre-genomic, albeit a mainly molecular, view of the topic.

Genomics of Aspergillus oryzae: learning from the history of Koji mold and exploration of its future

At a time when the notion of microorganisms did not exist, our ancestors empirically established methods for the production of various fermentation foods: miso (bean curd seasoning) and shoyu (soy sauce), both of which have been widely used and are essential for Japanese cooking, and sake, a magical alcoholic drink consumed at a variety of ritual occasions, are typical examples. A filamentous fungus, Aspergillus oryzae, is the key organism in the production of all these traditional foods, and its solid-state cultivation (SSC) has been confirmed to be the secret for the high productivity of secretory hydrolases vital for the fermentation process. Indeed, our genome comparison and transcriptome analysis uncovered mechanisms for effective degradation of raw materials in SSC: the extracellular hydrolase genes that have been found only in the A. oryzae genome but not in A. fumigatus are highly induced during SSC but not in liquid cultivation. Also, the temperature reduction process empirically adopted in the traditional soy-sauce fermentation processes has been found to be important to keep strong expression of the A. oryzae-specific extracellular hydrolases. One of the prominent potentials of A. oryzae is that it has been successfully applied to effective degradation of biodegradable plastic. Both cutinase, responsible for the degradation of plastic, and hydrophobin, which recruits cutinase on the hydrophobic surface to enhance degradation, have been discovered in A. oryzae. Genomic analysis in concert with traditional knowledge and technology will continue to be powerful tools in the future exploration of A. oryzae.

Some distinguishable properties between acid-stable and neutral types of alpha-amylases from acid-producing koji

The highly humid climate of Japan facilitates the growth of various molds. Among these molds, Aspergillus oryzae is the most important and popular in Japan, and has been used as yellow-koji in producing many traditional fermented beverages and foods, such as Japanese sake, and soy sauce. Taka-amylase A (TAA), a major enzyme produced by the mold, is well known worldwide to be a leading enzyme for industrial utilization and academic study, since many extensive studies have been carried out with TAA. In southern Kyushu, the other koji's of citric acid-producing molds have often been used, such as in the production of a traditional distilled liquor of shochu. The koji molds black-koji and white-koji produce two types of alpha-amylase, namely, acid-stable (AA) and common neutral (NA). The latter enzyme is enzymatically and genetically similar to TAA. In this review, we investigate AA from three molds, Aspergillus niger, A. kawachii and A. awamori, and the yeast Cryptococcus sp. regarding the distinguishable properties between AA and NA. (i) The N-terminus amino acid sequences of AA determined by molecular cloning started with the sequence of L-S-A-, whereas those of NA started with A-T-P-. (ii) Most of the full sequences of AA were composed of, besides a core catalytic domain, an extra domain of a hinge region and a carbohydrate binding domain, which could be responsible for raw-starch-digestibility. The AA from A. niger has no exceptionally extra domain, similarly to NA. (iii) Simple methods for distinguishing AA from NA using CNP-alpha-G3 and G5 as substrates were developed by our group. (iv) The number of subsite in AA on the basis of its cleavage pattern of maltooligosaccharides was estimated to be five, which differs from that of TAA, 7-9. AA has many advantages in industrial applications, such as its acid-stability, thermostability, and raw-starch digesting properties.

Deletion analysis of the catalase-encoding gene (catB) promoter from Aspergillus oryzae

The catalase-encoding gene (catB) is expressed strongly in Aspergillus oryzae. To identify the transcription regulatory elements involved in strong expression, we did promoter deletion analysis using beta-glucuronidase (GUS) as a reporter and an electrophoretic gel mobility shift assay (EMSA) systematically. The deletion 200-bp sequence from -1,000 to -800 in the 1,400-bp catB promoter caused a drastic decrease in GUS activity. In addition, EMSA implicated a 45-bp element from -1,000 to -956 containing cis-elements. According to detailed promoter deletion analysis, a region from -1,000 to -975, which contains putative heat shock element (HSE) and the CCAAT-box, was involved in strong expression.

The glucoamylase-encoding gene (glaB) is expressed in solid-state culture with a low water content

Solid-state culture encourages high-level enzyme secretion by Aspergillus oryzae. Using the real-time quantitative reverse transcriptase-polymerase chain reaction, we confirmed that expression of the glucoamylase-encoding gene in A. oryzae cultured in solid-state culture depends on the water content of the culture.

Analysis of expressed sequence tags from the fungus Aspergillus oryzae cultured under different conditions

We performed random sequencing of cDNAs from nine biologically or industrially important cultures of the industrially valuable fungus Aspergillus oryzae to obtain expressed sequence tags (ESTs). Consequently, 21 446 raw ESTs were accumulated and subsequently assembled to 7589 non-redundant consensus sequences (contigs). Among all contigs, 5491 (72.4%) were derived from only a particular culture. These included 4735 (62.4%) singletons, i.e. lone ESTs overlapping with no others. These data showed that consideration of culture grown under various conditions as cDNA sources enabled efficient collection of ESTs. BLAST searches against the public databases showed that 2953 (38.9%) of the EST contigs showed significant similarities to deposited sequences with known functions, 793 (10.5%) were similar to hypothetical proteins, and the remaining 3843 (50.6%) showed no significant similarity to sequences in the databases. Culture-specific contigs were extracted on the basis of the EST frequency normalized by the total number for each culture condition. In addition, contig sequences were compared with sequence sets in eukaryotic orthologous groups (KOGs), and classified into the KOG functional categories.

Isolation and Characterization of Two Genes That Encode Active Glucoamylase Without a Starch Binding Domain from Rhizopus oryzae

Glucoamylase obtained from Rhizopus sp. is frequently preferred for certain applications of starch modification or saccharification. The predominant enzyme, which contains a starch-binding domain on the amino terminus, has been previously characterized from several species. Additionally, the cDNA encoding this protein was cloned and found to show 100% identity to a R. oryzae strain 99-880 that has recently been sequenced by the Broad Institute of Harvard and Massachusetts Institute of Technology. Analysis of this genome indicates coding regions for two additional glucoamylase genes, amyC and amyD, lacking a starch-binding domain. The two genes encode proteins that are approximately 50% identical to the catalytic region of the AmyA protein and 67% identical to each other. The predicted AmyC and AmyD proteins contain the highly conserved signature sequences of Family 15 glycoside hydrolases. The two genes appear to be transcriptionally expressed in cultures grown in fermentable and gluconeogenic carbon sources. The predicted 49.7-kD AmyC and 48.8-kD AmyD proteins were expressed in several different ways using Pichia pastoris. When the sequence for putative secretion signal was left intact, glucoamylase activity was detected in the crude cell extracts, but no activity was present in the growth medium. However, replacement of this region with the yeast alpha-secretion signal resulted in secretion of active glucoamylase that was able to degrade soluble starch.

Deletion analysis of the superoxide dismutase (sodM) promoter from Aspergillus oryzae

The manganese superoxide dismutase gene (sodM) is very highly expressed in Aspergillus oryzae. To elucidate the basis for this high-level expression, deletion analysis of the promoter was undertaken using beta-glucuronidase (GUS) as a reporter. Deletion of a 63-bp sequence from -200 to -138 in the 1,038-bp sodM promoter caused a drastic decrease in GUS activity. In addition, an electrophoretic gel mobility shift assay (EMSA) implicated a 30-bp element from -209 to -178 containing cis-element(s) in the high-level expression. The results of fine structure deletion analysis of this region were consistent with the EMSA results. To confirm these findings, we constructed enhanced sodM promoters by incorporating tandem repeats of this region, which resulted in an approximate twofold increase in expression relative to the native sodM promoter.

Molecular breeding of Aspergillus kawachii overproducing cellulase and its application to brewing barley shochu

In order to improve fermentation of barley without addition of commercial cellulase, a white koji mold, Aspergillus kawachii IFO4308, was transformed with the egl1 gene encoding endoglucanase I (EGI) of Trichoderma viride and the endogenous cekA gene encoding endoglucanase (CekA). Transformants with egl1 under the control of the strong glaA promoter produced EGI in both submerged and solid-state cultures. However, the EGI produced in solid-state culture was unstable due to the acidic condition of this culture. A transformant N10 with two additional copies of the cekA gene exhibited endoglucanase activities against carboxymethyl-cellulose, which are 21- and 1.8-fold higher than that of the wild-type (wt) strain when the cells were cultivated in submerged and solid-state cultures, respectively. Cultivation of strain N10 in steamed barley for preparing koji followed by fermentation with Saccharomyces cerevisiae resulted in improved fermentation assessed based on higher productions of ethanol, amino acids, and organic acids, the reduction of residual sugar, and the low viscosity of barley mash. The overall fermentation result for the transformant carrying cekA was comparable with that for the wt strain using commercial cellulase. These results demonstrate that acquisition of only two-fold CekA activity by A. kawachii in the solid-state culture allows us to improve the brewing of barley shochu.

Cloning of a novel tyrosinase-encoding gene (melB) from Aspergillus oryzae and its overexpression in solid-state culture (Rice Koji)

We have cloned a novel tyrosinase-encoding gene (melB) specifically expressed in solid-state culture of Aspergillus oryzae. A tyrosinase-encoding gene (melO) from A. oryzae was already cloned and the protein structures of its catalytic and copper binding domains were investigated. However, our recent results revealed that the melO gene was highly expressed in submerged culture but not in solid-state culture. Because tyrosinase activity was also detected in solid-state culture, we assumed that another tyrosinase gene other than melO is expressed in solid-state culture. Another tyrosinase gene was screened using the expressed sequence tag (EST) library. One redundant cDNA clone homologous with the tyrosinase gene was found in the collection of wheat bran culture. Northern blot analysis revealed that the gene corresponding to the cDNA clone was specifically expressed in solid-state culture (koji making), but not in submerged culture. Molecular cloning showed that the gene carried six exons interrupted by five introns and had an open reading frame encoding 616 amino acid residues. This gene was designated as melB. The deduced amino acid sequence of the gene had weak homology (24%-33%) with MelO and other fungal tyrosinases but the sequences of the copper binding domains were highly conserved. When the melB gene was expressed under the control of the glaB promoter in solid-state culture, tyrosinase activity was markedly enhanced and the culture mass was browned with the melanization by MelB tyrosinase. These results indicated that the melB gene encodes a novel tyrosinase associated with melanization in solid-state culture.

Characteristics of alpha-glucosidase production from recombinant Aspergillus oryzae by membrane-surface liquid culture in comparison with various cultivation methods

alpha-Glucosidase was produced using recombinant Aspergillus oryzae by membrane-surface liquid culture (MSLC), a method previously developed by the authors and the results compared with other methods, including shaking flask culture (SFC), agar-plate culture (APC), culture on urethane sponge supports (USC), and liquid surface culture (LSC) to determine possible reasons for the advantageous features of MSLC. When yeast extract was used as a nitrogen source, the amount of enzyme produced by MSLC was 5 or more times higher than those for SFC and LSC, but similar to that using APC. Enzyme production in USC was slightly lower than in MSLC and APC. Cell growth was similar irrespective of the cultivation method used. When NaNO3, a typical inorganic nitrogen source was used, enzyme production in all the cultures was lower than that using yeast extract. However, even using NaNO3, the amount of the enzyme produced by MSLC was 8 to 20 times higher than those by SFC, APC, USC, and LSC. Although cell growth using NaNO3 was similar to that for yeast extract in MSLC, it was markedly decreased in SFC, APC, and LSC. The reason for the difference in enzyme productivity for various cultivation methods using yeast extract and NaNO3 as a nitrogen source is discussed, on the basis of the experimental findings. The role of the oxygen transfer effect and gene expression levels in enzyme production were also examined.

A novel amine oxidase-encoding gene from Aspergillus oryzae

We cloned a novel gene (aoxA) encoding amine oxidase (AOX) from Aspergillus oryzae. One cDNA clone showing extreme homology to the AOX-encoding genes was found in an expressed sequence tag (EST) library of A. oryzae. Molecular analysis revealed that the aoxA carried four exons interrupted by three introns and had an open reading frame encoding 672 amino acid residues. The deduced amino acid sequence showed about 83.5% identity to the Aspergillus niger AO-I. The strictly conserved residues for co-factor and copper binding in copper/quinine-containing AOXs were also preserved at Tyr 405, His 456, His 458 and His 617 in the cDNA sequence. When the aoxA was overexpressed in the homologous hyperexpression system of A. oryzae, AOX activity in the transformant was enhanced 75-fold. An apparent molecular weight of 159,000 by gel filtration and a subunit molecular weight of 75,000 by SDS-PAGE of the purified enzyme were estimated, suggesting that the enzyme molecule is a homo-dimer similar to other copper/quinine-containing AOXs. The A. oryzae AOXA preferentially oxidized aliphatic monoamines of C2-C6 rather than aromatic amines or diamines. From these results, the aoxA gene product obtained by homologous hyperexpression system of A. oryzae is undoubtedly a functional AOX.

Three-dimensional image analysis of plugging at the septal pore by Woronin body during hypotonic shock inducing hyphal tip bursting in the filamentous fungus Aspergillus oryzae

We observed that the filamentous fungus, Aspergillus oryzae, grown on agar media burst out cytoplasmic constituents from the hyphal tip soon after flooding with water. Woronin body is a specialized organelle known to plug the septal pore adjacent to the lysed compartment to prevent extensive loss of cytoplasm. A. oryzae Aohex1 gene homologous to Neurospora crassa HEX1 gene encoding a major protein in Woronin body was expressed as a fusion with DsRed2, resulting in visualization of Woronin body. Confocal microscopy and three-dimensional reconstruction of images visualized the septal pore as a dark region surrounded by green fluorescence of EGFP-fused secretory protein, RNase T1, on the septum. Dual fluorescent labeling revealed the plugging of the septal pores adjacent to the lysed apical compartments by Woronin bodies during hypotonic shock. Disruption of Aohex1 gene caused disappearance of Woronin bodies and the defect to prevent extensive loss of cytoplasm during hypotonic shock.