Background Nerol (C10H18O), an acyclic monoterpene, naturally presents in plant essential oils, and is used widely in food, cosmetics and pharmaceuticals as the valuable fragrance. Meanwhile, chemical synthesis is the only strategy for large-scale production of nerol, and the disadvantages of chemical synthesis greatly limit the production and its application. These defects drive the interests of researchers shift to the production of nerol by eco-friendly methods known as biosynthesis methods. However, the main technical bottleneck restricting the biosynthesis of nerol is the lacking of corresponding natural aroma-producing microorganisms. Results In this study, a novel multi-stress-tolerant probiotics Meyerozymaguilliermondii GXDK6 with aroma-producing properties was identified by whole genome sequencing and metabolomics technology. GXDK6 showed a broad pH tolerance in the range of 2.5–10.0. The species also showed salt tolerance with up to 12% NaCl and up to 18% of KCl or MgCl2. GXDK6 exhibited heavy-metal Mn2+ tolerance of up to 5494 ppm. GXDK6 could also ferment with a total of 21 kinds of single organic matter as the carbon source, and produce abundant aromatic metabolites. Results from the gas chromatography–mass spectrometry indicated the production of 8–14 types of aromatic metabolites (isopentanol, nerol, geraniol, phenylethanol, isobutanol, etc.) when GXDK6 was fermented up to 72 h with glucose, sucrose, fructose, or xylose as the single carbon source. Among them, nerol was found to be a novel aromatic metabolite from GXDK6 fermentation, and its biosynthesis mechanism had also been further revealed. Conclusion A novel aroma-producing M. guilliermondii GXDK6 was identified successfully by whole genome sequencing and metabolomics technology. GXDK6 showed high multi-stress-tolerant properties with acid–base, salty, and heavy-metal environments. The aroma-producing mechanism of nerol in GXDK6 had also been revealed. These findings indicated the aroma-producing M. guilliermondii GXDK6 with multi-stress-tolerant properties has great potential value in the fermentation industry.

Various agricultural products used in food fermentation are polluted by heavy metals, especially copper, which seriously endangers human health. Methods to remove copper with microbial strategies have gained interests. A novel Meyerozyma guilliermondii GXDK6 could survive independently under high stress of copper (1400 ppm). The copper tolerance mechanism of GXDK6 was revealed by integrated omics in this work. Whole-genome analysis showed that nine genes (i.e., CCC2, CTR3, FRE2, GGT, GST, CAT, SOD2, PXMP4, and HSP82) were related to GXDK6 copper tolerance. Copper stress elevated glutathione metabolism-related gene expression, glutathione content, and glutathione sulfur transferase activity, suggesting enhanced copper conjugation and detoxification in cells. The inhibited copper uptake by Ctr3 and enhanced copper efflux by Ccc2 contributed to the decrease in intracellular copper concentration. The improved expression of antioxidant enzyme genes (PXMP4, SOD2, and CAT), accompanied by the enhanced activities of antioxidant enzymes (peroxidase, superoxide dismutase, and catalase), decreased copper-induced reactive oxygen species production, protein carbonylation, lipid peroxidation, and cell death. The metabolite D-mannose against harsh stress conditions was beneficial to improving copper tolerance. This study contributed to understanding the copper tolerance mechanism of M. guilliermondii and its application in removing copper during fermentation.

A novel strain named Meyerozyma guilliermondii GXDK6 was provided in this work, which was confirmed to survive independently under high salt stress (12% NaCl) or co-stress condition of strong acid (pH 3.0) and high salts (10% NaCl) without sterilization. Its survival mechanism under high salt stress was revealed by integrated omics for the first time. Whole-genome analysis showed that 14 genes (e.g., GPD1 and FPS1) of GXDK6 relevant to salt tolerance were annotated and known to belong to various salt-resistant mechanisms (e.g., regulation of cell signal transduction and glycerol metabolism controls). Transcriptome sequencing results indicated that 1220 genes (accounting for 10.15%) of GXDK6 were differentially transcribed (p < 0.05) when GXDK6 growth was under 10% stress for 16 h, including important novel salt-tolerant-related genes (e.g., RTM1 and YHB1). Proteomics analysis demonstrated that 1005 proteins (accounting for 27.26%) of GXDK6 were differentially expressed (p < 0.05) when GXDK6 was stressed by 10% NaCl. Some of the differentially expressed proteins were defined as the novel salt-tolerant related proteins (e.g., sugar transporter STL1 and NADPH-dependent methylglyoxal reductase). Metabolomic analysis results showed that 63 types of metabolites (e.g., D-mannose, glycerol and inositol phosphate) of GXDK6 were up- or downregulated when stressed by 10% NaCl. Among them, D-mannose is one of the important metabolites that could enhance the salt-tolerance survival of GXDK6.

BackgroundNerol (C10H18O), an acyclic monoterpene, naturally presents in plant essential oils, and is used widely in food, cosmetics and pharmaceuticals as the valuable fragrance. Meanwhile, chemical synthesis is the only strategy for large-scale production of nerol, and the disadvantages of chemical synthesis greatly limited the production and its application. These defects drive the interests of researchers shift to the production of nerol by eco-friendly methods known as biosynthesis methods. However, the main technical bottleneck restricting the biosynthesis of nerol is the lacking of corresponding natural aroma-producing microorganisms.ResultsIn this study, a novel multi-stress-tolerant probiotics Meyerozyma guilliermondii GXDK6 with aroma-producing properties was identified by whole genome sequencing and metabolomics technology. GXDK6 showed a broad pH tolerance in the range of 2.5–10.0. The species also showed salt tolerance with up to 12% NaCl and up to 18% of KCl or MgCl2. GXDK6 exhibited heavy-metal Mn2+ tolerance of up to 5494 ppm. GXDK6 could also ferment with a total of 21 kinds of single organic matter as the carbon source, and produce abundant aromatic metabolites. Results from the gas chromatography–mass spectrometry indicated the production of 8–14 types of aromatic metabolites (isopentanol, nerol, geraniol, phenylethanol, isobutanol, etc.) when GXDK6 was fermented up to 72 h with glucose, sucrose, fructose, or xylose as the single carbon source. Among of them, nerol was found as a novel aromatic metabolite from GXDK6 fermentation, and its biosynthesis mechanism had also been further revealed.ConclusionA novel aroma-producing M. guilliermondii GXDK6 was identified successfully by whole genome sequencing and metabolomics technology. GXDK6 showed high multi-stress-tolerant properties with acid–base, salty, and heavy-metal environments. The aroma-producing mechanism of nerol in GXDK6 had also been revealed. These findings indicated the aroma-producing M. guilliermondii GXDK6 with multi-stress-tolerant properties has great potential value in the fermentation industry.