Regulation of aspartate-derived amino-acid metabolism in Zygosaccharomyces rouxii compared to Saccharomyces cerevisiae

Metagenomic and metaproteomic analyses of microbial amino acid metabolism during Cantonese soy sauce fermentation

Cantonese soy sauce is an important type of traditional Chinese brewed soy sauce that was developed in southern China, mainly in Guangdong. Due to the long fermentation period and complex microbiota in Cantonese soy sauce, there are few reports on the microbial metaproteomics of Cantonese soy sauce. In this study, integrative metagenomic and metaproteomic analyzes were used to identify the changes in the dominant microbiota and amino acid synthesis-related enzymes and metabolism during Cantonese soy sauce fermentation. Metagenomic analysis revealed that Tetragenococcus halophilus, Weissella confusa, Weissella paramesenteroides, Enterobacter hormaechei, and Aspergillus oryzae were the dominant microbiota. Using the Top 15 dominant microbiota identified by metagenomics as the database, LTQ Orbitrap Velos Pro ETD mass spectrometry was used to obtain metaproteomic information about the microbes in the soy sauce, and the results indicated that the active enzymes involved in the metabolism of amino acids were secreted by microorganisms such as A. oryzae, T. halophilus, and Zygosaccharomyces rouxii. During the Cantonese soy sauce fermentation process. Among them, early fermentation (0-15d) was dominated by A. oryzae and T. halophilus, mid-term fermentation (60-90d) was dominated by Z. rouxii, A. oryzae, and T. halophilus, and late fermentation (90-120d) was dominated by A. oryzae, Z. rouxii, and T. halophilus. Kyoto Encyclopedia of Genes and Genomes analysis revealed that the main enzymes involved in the metabolism of umami amino acids were aspartate aminotransferase, citrate synthase, aconitase, and isocitrate dehydrogenase, which were produced by Z. rouxii and A. oryzae during early fermentation (0-15 d) and the middle fermentation stage (60-90 d). This study constructed a regulatory network of enzymes potentially involved in the metabolism of flavor amino acids, which provided a theoretical basis for studying the amino acid metabolism of Cantonese soy sauce.

Comparative evaluation of microbial diversity and metabolite profiles in doenjang, a fermented soybean paste, during the two different industrial manufacturing processes

Two different doenjang manufacturing processes, the industrial process (IP) and the modified industrial process (mIP) with specific microbial assortments, were subjected to metabolite profiling using liquid chromatography-mass spectrometry (LC-MS) and gas chromatography time-of-flight mass spectrometry (GC-TOF-MS). The multivariate analyses indicated that both primary and secondary metabolites exhibited distinct patterns according to the fermentation processes (IP and mIP). Microbial community analysis for doenjang using denaturing gradient gel electrophoresis (DGGE), exhibited that both bacteria and fungi contributed proportionally for each step in the process viz., soybean, steaming, drying, meju fermentation, cooling, brining, and aging. Further, correlation analysis indicated that Aspergillus population was linked to sugar metabolism, Bacillus spp. with that of fatty acids, whereas Tetragenococcus and Zygosaccharomyces were found associated with amino acids. These results suggest that the components and quality of doenjang are critically influenced by the microbial assortments in each process.

Zygosaccharomyces rouxii strains CECT 11923 and Z. rouxii CECT 10425: Two new putative hybrids?

Based on IGS-PCR RFLP polymorphism, we previously detected two Z. rouxii strains (CECT 11923 and CECT 10425) that clustered with hybrid strains (NCYC 1682, NCYC 3060 and NCYC 3061). Given the recently recognized important industrial role of hybrids, their detection is very useful. Based on the IGS1 rDNA region alignment of hybrid strains and the Z. rouxii CECT 11923 and CECT 10425, in this work, we developed a pair of Zygosaccharomyces hybrid-specific primers, HibZF/HibZR. Positive amplicons were only obtained in the Zygosaccharomyces spp. hybrids included in this study and the CECT 11923 and CECT 10425 strains analyzed here. In the present study, we applied molecular tools to highlight the nature of these strains; they are quite different from each other as well as from Z. rouxii type strain. Based on the presence of two heterologous copies of nuclear-encoded genes (SOD2 and HIS3), the sequences of divergent 5.8S-ITS rDNA, D1/D2 26S rDNA copies and, the amplification with species-specific primer for Z. rouxii and Z. pseudorouxii, we hypothesize that the CECT 11923 strain might be a hybrid strain. Whereas, CECT 10425, the sequence analysis of 5.8S-ITS rDNA and D1/D2 26S rDNA copies presented 99-100% sequence identity with Zygosaccharomyces sp. NBRC 10669 (LN849119.1) and Z. sapae ABT 301^T. Nevertheless, we discard that it could be a Z. sapae strain based on the results obtained in this study. Namely, the amplification with hybrid-specific primer designed in this study, the number of divergent copies of HIS3 (2), the fact that it only possesses one SOD2 gene and the amplification with species-specific primer for Z. pseudorouxii, therefore it could be a new species or a hybrid strain.

Branched chain aldehydes: production and breakdown pathways and relevance for flavour in foods

Branched aldehydes, such as 2-methyl propanal and 2- and 3-methyl butanal, are important flavour compounds in many food products, both fermented and non-fermented (heat-treated) products. The production and degradation of these aldehydes from amino acids is described and reviewed extensively in literature. This paper reviews aspects influencing the formation of these aldehydes at the level of metabolic conversions, microbial and food composition. Special emphasis was on 3-methyl butanal and its presence in various food products. Knowledge gained about the generation pathways of these flavour compounds is essential for being able to control the formation of desired levels of these aldehydes.

Concomitant extracellular accumulation of alpha-keto acids and higher alcohols by Zygosaccharomyces rouxii

Alpha-keto acids are key intermediates in the formation of higher alcohols, important flavor components in soy sauce, and produced by the salt-tolerant yeast Zygosaccharomyces rouxii. Unlike most of the higher alcohols, the alpha-keto acids are usually not extracellularly accumulated by Z. rouxii when it is cultivated with ammonium as the sole nitrogen source. To facilitate extracellular accumulation of the alpha-keto acids from aspartate-derived amino acid metabolism, the amino acids valine, leucine, threonine and methionine were exogenously supplied during batch and A-star cultivations of (routants of) Z. rouxii. It was shown that all alpha-keto acids from the aspartate-derived amino acid metabolism, except alpha-ketobutyrate, could be extracellularly accumulated. In addition, it appeared from the concomitant extracellular accumulation of alpha-keto acids and higher alcohols that in Z. rouxii, valine, leucine and methionine were converted via Ehrlich pathways similar to those in Saccharomyces cerevisiae. Unlike these amino acids, threonine was converted via both the Ehrlich and amino acid biosynthetic pathways in Z. rouxii.

Effect of L-malic and citric acids metabolism on the essential amino acid requirements for Oenococcus oeni growth

AIMS

The purpose of this work was to study the effect of L-malic and/or citric acids on Oenococcus oeni m growth in deficient nutritional conditions, and their roles as possible biosynthetic precursors of the essential amino acids.

METHODS AND RESULTS

Bacterial cultures were performed in synthetic media. Bacterial growth rate was reduced or annulled when one amino acid was omitted from basal medium, especially for members of aspartate family, except lysine. The organic acids increased or restored the growth rates to the respective reference values. In each medium deficient in one essential amino acid, the L-malic acid utilization was accompanied by an increase of L-lactic acid concentration and accounted for approximately 100%l-malic acid consumed. D-lactic acid formation from glucose decreased in the medium without cysteine. Except for tyrosine, the recovery of glucose-citrate as D-lactic acid was lower than in the complete medium when asparagine, isoleucine or cysteine were excluded. The ethanol and acetate production was not modified.

CONCLUSIONS

L-malic and citric acids favoured Oenococcus oeni m growth in nutritional stress conditions. Specifically citric acid was involved in the biosynthesis of the aspartate-derived essential amino acids and glucose in the cysteine biosynthesis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Such beneficial effect of l-malic and citric acids on amino acids requirements of Oenococcus oeni m have great significance considering the low amino acids concentration in wine.