Tryptophan Derivatives by Saccharomyces cerevisiae EC1118: Evaluation, Optimization, and Production in a Soybean-Based Medium

Nicotinic acid availability impacts redox cofactor metabolism in Saccharomyces cerevisiae during alcoholic fermentation

Anaerobic alcoholic fermentation, particularly in high-sugar environments, presents metabolic challenges for yeasts. Crabtree-positive yeasts, including Saccharomyces cerevisiae, prefer fermentation even in the presence of oxygen. These yeasts rely on internal NAD+ recycling and extracellular assimilation of its precursor, nicotinic acid (vitamin B3), rather than de novo NAD+ production. Surprisingly, nicotinic acid assimilation is poorly characterized, even in S. cerevisiae. This study elucidated the timing of nicotinic acid uptake during grape juice-like fermentation and its impact on NAD(H) levels, the NAD+/NADH ratio, and metabolites produced. Complete uptake of extracellular nicotinic acid occurred premid-exponential phase, thereafter small amounts of vitamin B3 were exported back into the medium. Suboptimal levels of nicotinic acid were correlated with slower fermentation and reduced biomass, disrupting redox balance and impeding NAD+ regeneration, thereby affecting metabolite production. Metabolic outcomes varied with nicotinic acid concentrations, linking NAD+ availability to fermentation efficiency. A model was proposed encompassing rapid nicotinic acid uptake, accumulation during cell proliferation, and recycling with limited vitamin B3 export. This research enhances the understanding of nicotinic acid uptake dynamics during grape juice-like fermentation. These insights contribute to advancing yeast metabolism research and have profound implications for the enhancement of biotechnological practices and the wine-making industry.

Honey's Yeast-New Source of Valuable Species for Industrial Applications

Honey is a rich source of compounds with biological activity; moreover, it is a valuable source of various microorganisms. The aim of this study was to isolate and identify yeast from a sample of lime honey from Poland as well as to assess its ability to biosynthesize value-added chemicals such as kynurenic acid, erythritol, mannitol, and citric acid on common carbon sources. Fifteen yeast strains belonging to the species Yarrowia lipolytica, Candida magnolia, and Starmerella magnoliae were isolated. In shake-flask screening, the best value-added compound producers were chosen. In the last step, scaling up of the culture in the bioreactor was performed. A newly isolated strain of Y. lipolytica No. 12 produced 3.9 mg/L of kynurenic acid growing on fructose. Strain Y. lipolytica No. 9 synthesized 32.6 g/L of erythritol on technical glycerol with a low concentration of byproducts. Strain Y. lipolytica No. 5 produced 15.1 g/L of mannitol on technical glycerol, and strain No. 3 produced a very high amount of citric acid (76.6 g/L) on technical glycerol. In conclusion, to the best of our knowledge this is the first study to report the use of yeast isolates from honey to produce valuable chemicals. This study proves that natural products such as lime honey can be an excellent source of wild-type yeasts with valuable production properties.

Expanding the application of tryptophan: Industrial biomanufacturing of tryptophan derivatives

Tryptophan derivatives are various aromatic compounds produced in the tryptophan metabolic pathway, such as 5-hydroxytryptophan, 5-hydroxytryptamine, melatonin, 7-chloro-tryptophan, 7-bromo-tryptophan, indigo, indirubin, indole-3-acetic acid, violamycin, and dexoyviolacein. They have high added value, widely used in chemical, food, polymer and pharmaceutical industry and play an important role in treating diseases and improving life. At present, most tryptophan derivatives are synthesized by biosynthesis. The biosynthesis method is to combine metabolic engineering with synthetic biology and system biology, and use the tryptophan biosynthesis pathway of Escherichia coli, Corynebacterium glutamicum and other related microorganisms to reconstruct the artificial biosynthesis pathway, and then produce various tryptophan derivatives. In this paper, the characteristics, applications and specific biosynthetic pathways and methods of these derivatives were reviewed, and some strategies to increase the yield of derivatives and reduce the production cost on the basis of biosynthesis were introduced in order to make some contributions to the development of tryptophan derivatives biosynthesis industry.

The microbial production of kynurenic acid using Yarrowia lipolytica yeast growing on crude glycerol and soybean molasses

Yarrowia lipolytica yeast are able to produce kynurenic acid—a very valuable compound acting as a neuroprotective and antioxidant agent in humans. The recent data proved the existence of the kynurenine biosynthesis pathway in this yeast cells. Due to this fact, the aim of this work was to enhance kynurenic acid production using crude glycerol and soybean molasses as cheap and renewable carbon and nitrogen sources. The obtained results showed that Y. lipolytica GUT1 mutants are able to produce kynurenic acid in higher concentrations (from 4.5 mg dm⁻³ to 14.1 mg dm⁻³) than the parental strain (3.6 mg dm⁻³) in the supernatant in a medium with crude glycerol. Moreover, the addition of soybean molasses increased kynurenic acid production by using wild type and transformant strains. The A-101.1.31 GUT1/1 mutant strain produced 17.7 mg dm⁻³ of kynurenic acid in the supernatant during 150 h of the process and 576.7 mg kg⁻¹ of kynurenic acid in dry yeast biomass. The presented work proves the great potential of microbial kynurenic acid production using waste feedstock. Yeast biomass obtained in this work is rich in protein, with a low content of lipid, and can be a healthy ingredient of animal and human diet.

Isotopic labelling-based analysis elucidates biosynthesis pathways in Saccharomyces cerevisiae for Melatonin, Serotonin and Hydroxytyrosol formation

Yeasts can synthetise bioactive compounds such as Melatonin (MEL), Serotonin (SER) and Hydroxytyrosol (HT). Deciphering the mechanisms involved in their formation can lead to exploit this fact to increase the bioactive potential of fermented beverages. Quantitative analysis using labelled compounds, 15-N2 l-tryptophan and 13-C tyrosine, allowed tracking the formation of the above-mentioned bioactive compounds during the alcoholic fermentation of synthetic must by two different Saccharomyces cerevisiae strains. Labelled and unlabelled MEL, SER and HT were undoubtedly identified and quantified by High Resolution Mass Spectrometry (HRMS). Our results prove that there are at least two pathways involved in MEL biosynthesis by yeast. One starts with tryptophan as precursor being known for the vertebrates' pathway. Additionally, MEL is produced from SER which in turn is consistent with the plants' biosynthesis pathway. Concerning HT, it can be formed both from labelled tyrosine and from intermediates of the Erlich pathway.