Yeast diversity during the spontaneous fermentation of wine with only the microbiota on grapes cultivated in Japan.

Making wine via spontaneous fermentation without sulfur dioxide and commercial yeast (spontaneous winemaking) is increasing in recent year, but there is scant research regarding microbial communities present in Japan during spontaneous winemaking using culture-independent molecular methods. We analyzed fungal communities and populations during laboratory-scale spontaneous winemaking using sterilized labware to avoid winery-resident microbes. In the spontaneous fermentation of four grape varieties (Pinot Noir, Riesling, Koshu, and Koshusanjaku) grown in the same Japanese vineyard, our analysis of yeast and other fungal species by next-generation sequencing based on the ITS1 region demonstrated that Saccharomyces cerevisiae was eventually dominant in seven of 12 fermentation batches (three replications for each grape variety), whereas non-Saccharomyces species (e.g., Schizosaccharomyces japonicus, Lachancea dasiensis, and Hanseniaspora valbyensis) became dominant in four batches at the end of fermentation. In another batch, lactic acid bacteria (LAB) became dominant and the fermentation remained incomplete. Diverse microbes were involved in the spontaneous fermentation (particularly in Koshusanjaku), indicating that residual sugar remained and lactic and acetic acid largely increased. Compared to the control wine made with SO2 and commercial yeast, the concentration of lactic acid was 47-fold higher in the must dominated by L. dasiensis, and the concentrations of acetic acid and lactic acid were 10-fold and 20-fold higher in the must dominated by LAB, respectively. Even when indigenous S. cerevisiae became dominant, the finished wines obtained high sensory-analysis scores for complexity but low scores for varietal typicality, indicating the risk of fermentation with unselected wild yeast on the grapes grown in Japan.

Genetic architecture of berry aroma compounds in a QTL (quantitative trait loci) mapping population of interspecific hybrid grapes (Vitis labruscana × Vitis vinifera).

BACKGROUND: Although grapes accumulate diverse groups of volatile compounds, their genetic regulation in different cultivars remains unelucidated. Therefore, this study investigated the volatile composition in the berries of an interspecific hybrid population from a Vitis labruscana 'Campbell Early' (CE) × Vitis vinifera 'Muscat of Alexandria' (MA) cross to understand the relationship among volatile compounds and their genetic regulation. Then, a quantitative trait locus (QTL) analysis of its volatile compounds was conducted. RESULTS: While MA contained higher concentrations of monoterpenes and norisoprenoids, CE contained higher concentrations of C6 compounds, lactones and shikimic acid derivatives, including volatiles characteristic to American hybrids, i.e., methyl anthranilate, o-aminoacetophenone and mesifurane. Furthermore, a cluster analysis of volatile profiles in the hybrid population discovered ten coordinately modulated free and bound volatile clusters. QTL analysis identified a major QTL on linkage group (LG) 5 in the MA map for 14 monoterpene concentrations, consistent with a previously reported locus. Additionally, several QTLs detected in the CE map affected the concentrations of specific monoterpenes, such as linalool, citronellol and 1,8-cineol, modifying the monoterpene composition in the berries. As for the concentrations of five norisoprenoids, a major common QTL on LG2 was discovered first in this study. Several QTLs with minor effects were also discovered in various volatile groups, such as lactones, alcohols and shikimic acid derivatives. CONCLUSIONS: An overview of the profiles of aroma compounds and their underlying QTLs in a population of interspecific hybrid grapes in which muscat flavor compounds and many other aroma compounds were mixed variously were elucidated. Coordinate modulation of the volatile clusters in the hybrid population suggested an independent mechanism for controlling the volatiles of each group. Accordingly, specific QTLs with significant effects were observed for terpenoids, norisoprenoids and some volatiles highly contained in CE berries.

Modeling the sake brewing characteristics of rice from brown rice metabolites.

Sake, soy sauce, miso (Japanese bean paste), and beer are made from grains. The characteristics of the grain significantly affect the quality of the final product. Many studies have been performed to evaluate the sake-brewing characteristics of rice. However, current rice analysis methods are time and labor intensive and require large samples. We developed a novel method for predicting the brewing characteristics of sake rice using <1 g of sample. Brown rice extracts were analyzed by ultrahigh-performance liquid chromatography quadrupole time-of-flight mass spectrometry, and mass chromatogram data were used as explanatory variables. The objective variables were the physical and chemical properties of the rice, the enzymatic activity of the rice-koji, the fermentation properties of the sake mash, the standard analytical values of the sake, and the flavor component concentrations in the sake. Prediction models were developed using the orthogonal projections to latent structures method. The prediction performances of the models were verified, and 32 out of the 54 objective variables were used in well-performing models. In conclusion, we developed a method for predicting the rice properties and brewing characteristics from results acquired by analyzing <1 g of brown rice. The method is a powerful tool for breeding new sake rice cultivars for good brewing characteristics in early generations and will improve our understanding of fluctuations in the brewing characteristics of sake rice before each sake brewing season starts.

1H-NMR metabolomics-based classification of Japanese sake and comparative metabolome analysis by gas chromatography-mass spectrometry.

Six categories of Japanese sake have been established by the National Tax Agency of Japan. In this system, the rice polishing ratio and the addition of alcohol are the main criteria for classification. The most common nuclear magnetic resonance (NMR) spectrometry method is 1H-NMR, and has higher throughput than gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS) analysis due to its short measurement time, easy sample preparation, and high reproducibility. However, owing to the production of dominant ethanol signals, metabolome analyses have not been used for classifying Japanese sake using 1H-NMR. In this study, a technique to selectively suppress ethanol signals was used to classify Japanese sake by 1H-NMR, and a model was constructed to predict the rice polishing ratio. The results were compared to those obtained by GC-MS. The suppression of ethanol signals enabled the detection of trace components by 1H-NMR. In a principal component analysis (PCA) score plot of 1H-NMR spectra with ethanol signal suppression, PC1 was associated with both the addition of alcohol and the rice polishing ratio. Additionally, the separation of samples observed was similar when PCA score plots of 1H-NMR and GC-MS data were compared. Similarly, to predict the rice polishing ratio using partial least squares regression analysis, a model was constructed using 1H-NMR data, and showed nearly similar values for precision and predictive performance with the model constructed using GC-MS data. These results suggest that metabolomic analyses of Japanese sake based on 1H-NMR spectral patterns may be useful for classification.

Effect of koji starter on metabolites in Japanese alcoholic beverage sake made from the sake rice Koshitanrei.

In sake brewing, the steamed rice is used in 2 ways, added to sake-mash and making rice-koji. Rice-koji is made from the steamed rice by using koji starter, and its quality is an important determinant of the aroma/taste of sake. The sake rice Koshitanrei (KOS) was developed in Niigata Prefecture by crossing 2 sake rice varieties, Gohyakumangoku and Yamadanishiki. Recently, we reported the characteristic components/metabolites in sake made from KOS by conducting metabolome analysis using UPLC-QTOF-MS. In this study, to investigate the effect of koji starter and sake rice cultivars on the sake metabolites, we performed small-scale sake-making tests using the above 3 rice cultivars and 3 koji starters. Finally, we demonstrated that some of the characteristic components/metabolites of sake from KOS are affected by the koji starter. Thus, in addition to rice cultivar, koji starter plays an important role for establishment/maintenance of the quality of the final product.

Variation in the mineral composition of wine produced using different winemaking techniques.

It has been reported that the concentrations of minerals in wines can be used to discriminate their geographical origin. However, some winemaking techniques may also affect the mineral concentration of the final product. In this study, we examined the effects of various winemaking techniques, including (i) fining, (ii) aging with oak tips, (iii) maceration with grape skins, (iv) chaptalization and acidification, and (v) yeast nutrient addition for alcohol fermentation, on the concentration of 18 minerals (Li, B, Na, Mg, Si, P, S, K, Ca, Mn, Co, Ni, Ga, Rb, Sr, Mo, Ba and Pb) in a total of 154 wine samples using grapes from different production areas. Among the various winemaking techniques, maceration with grape skin had the largest effect on mineral content, significantly changing the concentrations of 17 or 18 elements (B, Na, Mg, Si, P, S, K, Ca, Mn, Co, Ni, Ga, Rb, Sr, Mo, Ba and Pb). Fining treatment using bentonites had the second largest effect, altering the concentrations of 14 elements (Li, B, Na, Si, P, S, Ca, Co, Ga, Rb, Sr, Mo, Ba and Pb). However, in principal component analysis using all data (n = 154), the wine samples were clearly clustered according to grapes used in the experiments rather than the winemaking technique. In conclusion, some winemaking techniques significantly altered the concentration of some minerals in wine; however, the principal factor influencing wine mineral composition seems to be its geographical origin.

Author Correction: BiFC-based visualisation system reveals cell fusion morphology and heterokaryon incompatibility in the filamentous fungus Aspergillus oryzae.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Analysis of metabolites in Japanese alcoholic beverage sake made from the sake rice Koshitanrei.

In sake brewing, the steamed rice is used in two ways, added to sake-mash (as kake-mai) and making koji. The rice is an important determinant for the quality of sake, as the metabolites in sake affect its taste/aroma. The sake rice Koshitanrei (KOS) was developed in Niigata Prefecture by genetically crossing two sake rice, Gohyakumangoku and Yamadanishiki. However, the metabolites in sake from KOS have not been analyzed. Here, to investigate the characteristic metabolites in sake from KOS, we performed two types of small-scale sake-fermentation tests changing only the rice used for kake-mai or total rice (both kake-mai and koji) by these three rice cultivars and examined the effect of KOS on sake metabolites by the metabolome analysis method using UPLC-QTOF-MS. We identified the peaks/metabolites, whose intensity in sake from KOS was higher/lower than those from the other cultivars. The brewing properties of KOS were partially characterized by this analysis.

Investigation of relationship between sake-making parameters and sake metabolites using a newly developed sake metabolome analysis method.

We developed a sake metabolome analysis method using liquid chromatography-quadrupole/time-of-flight mass spectrometry to investigate the metabolome of various types of sakes and other alcohol beverages. Our method identified 198 compounds by comparison with standard metabolites. Using this method, we investigated the relationship between several sake-making parameters and sake metabolites by conducting combination experiments of these parameters using small-scale fermentation. The results indicated that all parameters significantly affected sake metabolites (P < 0.005) and most peaks were affected by multiple sake-making parameters. Interestingly, the effect of the rice cultivar on sake metabolites was higher for koji rice than for kake-rice. This result suggests that the rice cultivar used has a greater effect on the characteristics of Aspergillus oryzae compared to sake yeast and affects sake metabolites. In this study, we also evaluated the combined effect of several parameters. We demonstrated the different effects of each parameter on several amino acids. The results showed a new aspect of the science of sake making. For example, the amount of α-ethylglucoside, which can affect the taste of sake, was negatively correlated with α-glucosidase activity in koji (r = -0.84). In this study, various unidentified peaks were observed; detectable peaks can be increased by analyzing additional standard reagents. Investigating these unidentified peaks and accumulating datasets for sake-making parameters will give us insight into how to improve sake taste and quality.

Inter-strain expression of sequence-diverse HET domain genes severely inhibits growth of Aspergillus oryzae.

In the Pezizomycotina (filamentous ascomycete) species, genes that encode proteins with an HET domain (Pfam: PF06985) are reportedly involved in heterokaryon incompatibility (HI) in which cell death or growth defects are induced after fusion of cells that are genetically incompatible owing to diversities in their nucleotide sequence. HET domain genes are commonly found in Pezizomycotina genomes and are functionally characterized in only a few species. Here, we compared 44 HET domain genes between an incompatible strain pair of Aspergillus oryzae RIB40 and RIB128 and performed inter-strain expression of 37 sequence-diverse genes for mimicking HI. Four HET domain genes were identified to cause severe growth inhibition in a strain- or sequence-specific manner. Furthermore, SNPs responsible for the inhibition of cell growth were identified. This study provides an important insight into the physiological significance of sequence diversity of HET domain genes and their potential functions in HI of A. oryzae.

The potential aroma and flavor compounds in Vitis sp. cv. Koshu and V. vinifera L. cv. Chardonnay under different environmental conditions.

BACKGROUND: Koshu, a hybrid of Vitis vinifera L. and V. davidii Foex, is the most popular indigenous cultivar for wine production in Japan. However, little is known about the potential aroma compounds it contains and how environmental factors affect these. In this study, we obtained comprehensive profiles of the volatile (both glycosidically bound and free) and phenolic compounds that occur in koshu berries, and compared these with similar profiles for V. vinifera cv. chardonnay. We then compared the response of these two cultivars to bunch shading and the ripening-related phytohormone abscisic acid (ABA). RESULTS: Koshu berries contained significantly higher concentrations of phenolic compounds, such as hydroxycinnamic acid derivatives, and some volatile phenols, such as 4-vinyl guaiacol and eugenol, than chardonnay berries, which are thought to contribute to the characteristics of koshu wine. In addition, koshu berries had a distinctly different terpenoid composition from chardonnay berries. Shading reduced the concentration of norisoprenoid in both cultivars, as well as several phenolic compounds, particularly their volatile derivatives in koshu berries. The exogenous application of ABA induced ripening and increased the concentrations of lipid derivatives, such as hexanol, octanol, 1-nonanol, and 1-octen-3-ol. Multivariate and discriminant analyses showed that the potential aroma and flavor compounds in the berries could be discriminated clearly based on cultivar and environmental cues, such as light exposure. CONCLUSION: The unique secondary metabolite profiles of koshu and their different responses to environmental factors could be valuable for developing various types of koshu wines and new cultivars with improved quality and cultural characteristics. © 2018 Society of Chemical Industry.

BiFC-based visualisation system reveals cell fusion morphology and heterokaryon incompatibility in the filamentous fungus Aspergillus oryzae.

Aspergillus oryzae is an industrially important filamentous fungus used for Japanese traditional food fermentation and heterologous protein production. Although cell fusion is important for heterokaryon formation and sexual/parasexual reproduction required for cross breeding, knowledge on cell fusion and heterokaryon incompatibility in A. oryzae is limited because of low cell fusion frequency. Therefore, we aimed to develop a BiFC system to specifically visualise fused cells and facilitate the analysis of cell fusion in A. oryzae. The cell fusion ability and morphology of 15 A. oryzae strains were investigated using heterodimerising proteins LZA and LZB fused with split green fluorescence protein. Morphological investigation of fused cells revealed that cell fusion occurred mainly as conidial anastomosis during the early growth stage. Self-fusion abilities were detected in most industrial A. oryzae strains, but only a few strain pairs showed non-self fusion. Protoplast fusion assay demonstrated that almost all the pairs capable of non-self fusion were capable of heterokaryon formation and vice versa, thus providing the first evidence of heterokaryon incompatibility in A. oryzae. The BiFC system developed in this study provides an effective method in studying morphology of fused cells and heterokaryon incompatibility in the filamentous fungal species with low cell fusion efficiency.

Construction of sake yeast with low production of dimethyl trisulfide precursor by a self-cloning method.

Dimethyl trisulfide (DMTS) is the primary component responsible for "hineka", the stale aroma of Japanese sake. Deletion of the MRI1 or MDE1 gene of sake yeast, encoding 5'-methylthioribose-1-phosphate isomerase and 5'-methylthioribulose-1-phosphate dehydratase, respectively, has been reported to greatly reduce the amount of DMTS precursor (DMTS-P1) in sake and to suppress the formation of DMTS during storage. In this study, we constructed sake yeast strains lacking MRI1 gene function by a self-cloning method. Two methods were applied: in one, a stop codon was introduced in the MRI1 ORF by point mutation; in the other, the entire MRI1 ORF was deleted from the genome. In both methods, a plasmid vector containing drug-resistance and counter-selectable markers was used to introduce the mutation. We successfully obtained the strains, which did not contain the plasmid sequences, by both methods. Small-scale sake brewing tests using these SC strains (strains obtained by the self-cloning method) found that DMTS-P1 was hardly detected in sake brewed with SC strains, and DMTS production after sake storage was greatly reduced as compared with the parent strain. The components of brewed sake were almost the same between the SC and parent strains. These results suggest that SC strains can produce sake with higher flavor stability without changing the sake brewing properties.

Discrimination of wine from grape cultivated in Japan, imported wine, and others by multi-elemental analysis.

Differences in mineral concentrations were examined among three types of wine in the Japanese market place: Japan wine, imported wine, and domestically produced wine mainly from foreign ingredients (DWF), where Japan wine has been recently defined by the National Tax Agency as domestically produced wine from grapes cultivated in Japan. The main objective of this study was to examine the possibility of controlling the authenticity of Japan wine. The concentrations of 18 minerals (Li, B, Na, Mg, Si, P, S, K, Ca, Mn, Co, Ni, Ga, Rb, Sr, Mo, Ba, and Pb) in 214 wine samples were determined by inductively coupled-plasma mass spectrometry (ICP-MS) and ICP-atomic emission spectrometry (ICP-AES). In general, Japan wine had a higher concentration of potassium and lower concentrations of eight elements (Li, B, Na, Si, S, Co, Sr, and Pb) as compared with the other two groups of wine. Linear discriminant analysis (LDA) models based on concentrations of the 18 minerals facilitated the identification of three wine groups: Japan wine, imported wine, and DWF with a 91.1% classification score and 87.9% prediction score. In addition, an LDA model for discrimination of wine from four domestic geographic origins (Yamanashi, Nagano, Hokkaido, and Yamagata Prefectures) using 18 elements gave a classification score of 93.1% and a prediction score of 76.4%. In summary, we have shown that an LDA model based on mineral concentrations is useful for distinguishing Japan wine from other wine groups, and can contribute to classification of the four main domestic wine-producing regions of Japan.

Characterization of amylolytic enzyme overproducing mutant of Aspergillus luchuensis obtained by ion beam mutagenesis.

Aspergillus luchuensis is a kuro (black) koji fungus that has been used as a starch degrader for the awamori- and shochu-making industries in Japan. In this study, we investigated the effect of ion beam irradiation on A. luchuensis RIB2601 and obtained a high starch-degrading mutant strain U1. Strain U1 showed reduced growth rate, whereas it showed higher α-amylase, glucoamylase, and α-glucosidase activities on a mycelial mass basis than the wild type (wt) strain both on agar plates and in rice koji. In addition, strain U1 showed higher N-acetylglucosamine content in the cell wall and higher sensitivity to calcofluor white, suggesting a deficiency in cell wall composition. Interestingly, produced protein showed higher expression of acid-labile α-amylase (AmyA) and glucoamylase (GlaA) in strain U1, although real-time RT-PCR indicated no significant change in the transcription of the amyA or glaA gene. These results suggested that the high amylolytic activity of strain U1 is attributable to a high AmyA and GlaA production level, but the elevated production is not due to transcriptional regulation of the corresponding genes. Furthermore, RNA-seq analysis indicated that strain U1 shows transcriptional changes in at least 604 genes related to oxidation-reduction, transport, and glucosamine-containing compound metabolic processes, which may be involved in the deficient cell wall composition of strain U1.

Highly efficient gene targeting in Aspergillus oryzae industrial strains under ligD mutation introduced by genome editing: Strain-specific differences in the effects of deleting EcdR, the negative regulator of sclerotia formation.

Numerous strains of Aspergillus oryzae are industrially used for Japanese traditional fermentation and for the production of enzymes and heterologous proteins. In A. oryzae, deletion of the ku70 or ligD genes involved in non-homologous end joining (NHEJ) has allowed high gene targeting efficiency. However, this strategy has been mainly applied under the genetic background of the A. oryzae wild strain RIB40, and it would be laborious to delete the NHEJ genes in many A. oryzae industrial strains, probably due to their low gene targeting efficiency. In the present study, we generated ligD mutants from the A. oryzae industrial strains by employing the CRISPR/Cas9 system, which we previously developed as a genome editing method. Uridine/uracil auxotrophic strains were generated by deletion of the pyrG gene, which was subsequently used as a selective marker. We examined the gene targeting efficiency with the ecdR gene, of which deletion was reported to induce sclerotia formation under the genetic background of the strain RIB40. As expected, the deletion efficiencies were high, around 60~80%, in the ligD mutants of industrial strains. Intriguingly, the effects of the ecdR deletion on sclerotia formation varied depending on the strains, and we found sclerotia-like structures under the background of the industrial strains, which have never been reported to form sclerotia. The present study demonstrates that introducing ligD mutation by genome editing is an effective method allowing high gene targeting efficiency in A. oryzae industrial strains.

Polyphenolic diversity and characterization in the red-purple berries of East Asian wild Vitis species.

Grapes (Vitis spp.) produce diverse polyphenolic compounds, which are phytochemicals that contribute to human health. In this study, the polyphenolic profiles of the red-purple berries of two wild grape species native to Japan, Vitis ficifolia and V. coignetiae, and their interspecific hybrid cultivars were investigated and compared with the profiles of V. vinifera and V. × labruscana cultivars. Proanthocyanidins (PAs) were present at lower concentrations in both skins and seeds of wild grape species and their hybrid cultivars than those in V. vinifera cultivars. They also differed in their composition, consisting mainly of epicatechin in wild grape species, but containing considerable amounts of both epigallocatechin in the skins and epicatechin gallate in the seeds of V. vinifera. In contrast, V. ficifolia varieties and their hybrid cultivars accumulated high concentrations of diverse anthocyanins, and whose compositions of anthocyanins and flavonols differed between species in their degree of modification by glucosylation, acylation, methylation and B-ring hydroxylation. Principal component analysis (PCA) indicated that the polyphenolic constituents clearly separate V. vinifera and V. × labruscana cultivars from the wild grape species as well as between wild grape species, V. coignetiae and V. ficifolia. Intermediate compositions were also observed in the hybrid cultivars between these wild grape species and V. vinifera.

Development of a promoter shutoff system in Aspergillus oryzae using a sorbitol-sensitive promoter.

Promoter shutoff is a general method for analyzing essential genes, but in the fungus Aspergillus oryzae, no tightly repressed promoters have been reported. To overcome the current limitations of conditional promoters, we examined sorbitol- and galactose-responsive genes using microarrays to identify regulatable genes with only minor physiological and genetic effects. We identified two sorbitol-induced genes (designated as sorA and sorB), cloned their promoters, and built a regulated egfp and brlA expression system. Growth medium-dependent enhanced green fluorescence protein (EGFP) fluorescence and conidiation were confirmed for egfp and brlA under the control of their respective promoters. We also used this shutoff system to regulate the essential rhoA, which demonstrated the expected growth inhibition under repressed growth conditions. Our new sorbitol promoter shutoff system developed can serve as a valuable new tool for essential gene analyses of filamentous fungi.

Complete genome sequence of Lactobacillus acetotolerans RIB 9124 (NBRC 13120) isolated from putrefied (hiochi) Japanese sake.

Lactobacillus acetotolerans RIB 9124 (NBRC 13120) was isolated from putrefied (hiochi) Japanese sake. Here we report the complete genome sequence of this organism. This paper is the first report demonstrating the fully sequenced and completely annotated genome of a L. acetotolerans strain.

Gas chromatography/mass spectrometry based component profiling and quality prediction for Japanese sake.

Sake is a Japanese traditional alcoholic beverage, which is produced by simultaneous saccharification and alcohol fermentation of polished and steamed rice by Aspergillus oryzae and Saccharomyces cerevisiae. About 300 compounds have been identified in sake, and the contribution of individual components to the sake flavor has been examined at the same time. However, only a few compounds could explain the characteristics alone and most of the attributes still remain unclear. The purpose of this study was to examine the relationship between the component profile and the attributes of sake. Gas chromatography coupled with mass spectrometry (GC/MS)-based non-targeted analysis was employed to obtain the low molecular weight component profile of Japanese sake including both nonvolatile and volatile compounds. Sake attributes and overall quality were assessed by analytical descriptive sensory test and the prediction model of the sensory score from the component profile was constructed by means of orthogonal projections to latent structures (OPLS) regression analysis. Our results showed that 12 sake attributes [ginjo-ka (aroma of premium ginjo sake), grassy/aldehydic odor, sweet aroma/caramel/burnt odor, sulfury odor, sour taste, umami, bitter taste, body, amakara (dryness), aftertaste, pungent/smoothness and appearance] and overall quality were accurately explained by component profiles. In addition, we were able to select statistically significant components according to variable importance on projection (VIP). Our methodology clarified the correlation between sake attribute and 200 low molecular components and presented the importance of each component thus, providing new insights to the flavor study of sake.