Thiamine and Biotin: Relevance in the Production of Volatile and Non-Volatile Compounds during Saccharomyces cerevisiae Alcoholic Fermentation in Synthetic Grape Must

Transcriptome analysis and reverse engineering verification of SNZ3Val125Ile and Pho3Asn134Asp revealed the mechanism of adaptive laboratory evolution to increase the yield of tyrosol in Saccharomyces cerevisiae strain S26-AE2

BACKGROUND

Tyrosol is an important drug precursor, and Saccharomyces cerevisiae is one of the main microorganisms that produces tyrosol. Although excessive metabolic modification increases the production of tyrosol, it also causes a decrease in the growth rate of yeast. Therefore, this study attempted to restore the growth of S. cerevisiae through adaptive evolution and further improve tyrosol production.

RESULTS

After the adaptive laboratory evolution of S. cerevisiae S26, three evolutionary strains were obtained. The biomass of strain S26-AE2 reached 17.82 g DCW/L in the presence of 100 g/L glucose, which was 15.33% higher than that of S26, and its tyrosol production reached 817.83 mg/L. The transcriptome analysis revealed that, upon exposure to 100 g/L glucose, the S26-AE2 strain may reduce the transcriptional regulation of glucose repression through decreased HXK2 expression. The expression of genes related to pyruvate synthesis was increased in strain S26-AE2. Meanwhile, the expression levels of most tricarboxylic acid cycle-related genes in S26-AE2 were increased when cultured with 20 g/L glucose. Furthermore, the amount of tyrosol produced by strain S26 with the SNZ3Val125Ile mutation increased by 17.01% compared with that of the control strain S26 following exposure to 100 g/L glucose.

CONCLUSIONS

In this study, a strain, S26-AE2, with good growth and tyrosol production performance was obtained by adaptive evolution. The transcriptome analysis revealed that the differences in the expression of genes involved in metabolic pathways in adaptive evolutionary strains may be related to yeast growth and tyrosol production. Further reverse engineering verified that the mutation of SNZ3 promoted tyrosol synthesis in S. cerevisiae in glucose-rich medium. This study provides a theoretical basis for the metabolic engineering of S. cerevisiae to synthesise tyrosol and its derivatives.

Effect of Ultra-High Pressure Homogenisation (UHPH) on the Co-Inoculation of Lachancea thermotolerans and Metschnikowia pulcherrima in Tempranillo Must

The utilisation of non-Saccharomyces yeasts in co-inoculation and non-thermal technologies for must sterilisation is becoming increasingly prevalent due to their notable utility and potential. This new approach optimises the fermentation process and contributes to facilitating the production of wines with distinctive characteristics, improving their stability, and without organoleptic repercussions. Two trials were conducted concurrently, designated as A and B, using the same Tempranillo red must. In each trial, UHPH-treated and untreated must (serving as the control) were compared. The non-Saccharomyces yeasts (Lachancea thermotolerans and Metschnikowia pulcherrima) were identical in both trials, and fermentations were terminated by a Saccharomyces cerevisiae inoculated after 7 days (ternary fermentation). In Trial A, different percentages of the initial inoculum were employed with respect to the total volume that must be fermented, with the objective of evaluating the influence and competitiveness between yeasts. Trial B was designed to investigate the impact of two nutrients that provide vitamins, energy, and protection from oxidative stress on the development of these yeasts and their metabolic expression. Microbiological analysis and measurements of oenological parameters were carried out, acidification was assessed, volatile compounds were analysed, and the colour spectrum was measured by spectrophotometry. It was observed in both trials that the prevalence of Lachancea thermotolerans (Lt) was longer than that of Metschnikowia pulcherrima (Mp) and that the use of quercetin + thiamine had a positive effect on yeast growth. Furthermore, the combination of Lt and Mp yeasts demonstrated remarkable synergy, resulting in the production of a substantial quantity of lactic acid (>5 g/L). With regard to aroma compounds, the UHPH must have exhibited a nearly twofold increase in ethyl lactate. Additionally, the total polyphenol index (TPI) was observed to be 8-10% higher in wines derived from UHPH musts, indicating that this technology may potentially safeguard against oxidation.

Competition for Nitrogen Resources: An Explanation of the Effects of a Bioprotective Strain Metschnikowia pulcherrima on the Growth of Hanseniaspora Genus in Oenology

As a biological alternative to the antimicrobial action of SO2, bioprotection has been proposed to winemakers as a means to limit or prevent grape musts microbial alteration. Competition for nitrogenous nutrients and for oxygen are often cited as potential explanations for the effectiveness of bioprotection. This study analyses the effect of a bioprotective M. pulcherrima strain on the growth of one H. valbyensis strain and one H. uvarum strain. Bioprotection efficiency was observed only against H. valbyensis inoculated at the two lowest concentrations. These results indicate a potential species-dependent efficiency of the bioprotective strain and a strong impact of the initial ratio between bioprotective and apiculate yeasts. The analysis of the consumption of nitrogen compounds revealed that leucine, isoleucine, lysine and tryptophan were consumed preferentially by all three strains. The weaker assimilation percentages of these amino acids observed in H. valbyensis at 24 h growth suggest competition with M. pulcherrima that could negatively affects the growth of the apiculate yeast in co-cultures. The slowest rate of O2 consumption of H. valbyensis strain, in comparison with M. pulcherrima, was probably not involved in the bioprotective effect. Non-targeted metabolomic analyses of M. pulcherrima and H. valbyensis co-culture indicate that the interaction between both strains particularly impact lysin and tryptophan metabolisms.

Analysis of heterologous expression of phaCBA promotes the acetoin stress response mechanism in Bacillus subtilis using transcriptomics and metabolomics approaches

Acetoin, a versatile platform chemical and popular food additive, poses a challenge to the biosafety strain Bacillus subtilis when produced in high concentrations due to its intrinsic toxicity. Incorporating the PHB synthesis pathway into Bacillus subtilis 168 has been shown to significantly enhance the strain's acetoin tolerance. This study aims to elucidate the molecular mechanisms underlying the response of B. subtilis 168-phaCBA to acetoin stress, employing transcriptomic and metabolomic analyses. Acetoin stress induces fatty acid degradation and disrupts amino acid synthesis. In response, B. subtilis 168-phaCBA down-regulates genes associated with flagellum assembly and bacterial chemotaxis, while up-regulating genes related to the ABC transport system encoding amino acid transport proteins. Notably, genes coding for cysteine and D-methionine transport proteins (tcyB, tcyC and metQ) and the biotin transporter protein bioY, are up-regulated, enhancing cellular tolerance. Our findings highlight that the expression of phaCBA significantly increases the ratio of long-chain unsaturated fatty acids and modulates intracellular concentrations of amino acids, including L-tryptophan, L-tyrosine, L-leucine, L-threonine, L-methionine, L-glutamic acid, L-proline, D-phenylalanine, L-arginine, and membrane fatty acids, thereby imparting acetoin tolerance. Furthermore, the supplementation with specific exogenous amino acids (L-alanine, L-proline, L-cysteine, L-arginine, L-glutamic acid, and L-isoleucine) alleviates acetoin's detrimental effects on the bacterium. Simultaneously, the introduction of phaCBA into the acetoin-producing strain BS03 addressed the issue of insufficient intracellular cofactors in the fermentation strain, resulting in the successful production of 70.14 g/L of acetoin through fed-batch fermentation. This study enhances our understanding of Bacillus's cellular response to acetoin-induced stress and provides valuable insights for the development of acetoin-resistant Bacillus strains.

Mixed biofilm formation by Oenococcus oeni and Saccharomyces cerevisiae: A new strategy for the wine fermentation process

Bacterial biofilms have attracted much attention in the food industry since this phenotype increases microbial resistance to environmental stresses. In wine-making, the biofilm produced by Oenococcus oeni is able to persist in this harsh environment and perform malolactic fermentations. Certain viticultural practices are interested in the simultaneous triggering of alcoholic fermentation by yeasts of the species Saccharomyces cerevisiae and malolactic fermentation by lactic acid bacteria. As yet, no data is available on the ability of these micro-organisms to produce mixed biofilms and promote fermentations. Here, the ability of S. cerevisiae and O. oeni to form mixed biofilms on different surfaces found in vinification was observed and analyzed using scanning electron microscopy experiments. Then, following co-inoculation with biofilm or planktonic cells microvinifications were carried out to demonstrate that the mixed biofilms developed on oak allow the efficient completion of fermentations because of their high resistance to stress. Finally, comparisons of the different metabolic profiles obtained by LC-MS were made to assess the impact of the mode of life of biofilms on wine composition.

Selection of a Probiotic for Its Potential for Developing a Synbiotic Peach and Grape Juice

Due to recent interest in the potential of probiotics as health promoters and the impact of health and environmental concerns on eating habits, non-dairy probiotic food products are required. This study aimed to evaluate the viability of different probiotic microorganisms in peach and grape juice (PGJ) with or without the prebiotic inulin and their antimicrobial activity against the foodborne pathogen Listeria monocytogenes and the juice spoilage microorganism Saccharomyces cerevisiae. Firstly, the viability of seven probiotic strains was studied in PGJ with an initial concentration of 107 CFU/mL for 21 days at 4 °C and for 3 days at 37 °C. In parallel, the physicochemical effect, the antimicrobial effect and the lactic acid production in PGJ were evaluated. Secondly, the probiotic with the best viability results was selected to study its antimicrobial effect against L. monocytogenes and S. cerevisiae, as well as ethanol and acetaldehyde production by the latter. L. casei showed the highest viability and grew in both refrigerated and fermentation conditions (1 log), produced the greatest lactic acid (5.12 g/L) and demonstrated in vitro anti-Listeria activity. Although the addition of the prebiotic did not improve the viability, lactic acid production or anti-Listeria activity of the probiotics, under the conditions studied, the prebiotic potential of inulin, support the design of a synbiotic juice. Finally, although none of the probiotic, fermentation products, or postbiotics showed any antimicrobial activity against L. monocytogenes or S. cerevisiae, the addition of L. casei to the PGJ significantly reduced the production of S. cerevisiae metabolite ethanol (29%) and acetaldehyde (50%). L. casei might be a suitable probiotic to deliver a safe and functional PGJ, although further research should be carried out to determine the effect of the probiotic and fermentation on the nutritional profile of PGJ.

Exploring fermentative metabolic response to varying exogenous supplies of redox cofactor precursors in selected wine yeast species

The use of non-Saccharomyces yeasts in winemaking is gaining traction due to their specific phenotypes of technological interest, including their unique profile of central carbon metabolites and volatile compounds. However, the lack of knowledge about their physiology hinders their industrial exploitation. The intracellular redox status, involving NAD/NADH and NADP/NADPH cofactors, is a key driver of yeast activity during fermentation, notably directing the formation of metabolites that contribute to the wine bouquet. The biosynthesis of these cofactors can be modulated by the availability of their precursors, nicotinic acid and tryptophan, and their ratio by that of thiamine. In this study, a multifactorial experiment was designed to assess the effects of these three nutrients and their interactions on the metabolic response of various wine yeast species. The data indicated that limiting concentrations of nicotinic acid led to a species-dependent decrease in intracellular NAD(H) concentrations, resulting in variations of fermentation performance and production of metabolic sinks. Thiamine limitation did not directly affect redox cofactor concentrations or balance, but influenced redox management and subsequently the production of metabolites. Overall, this study identified nicotinic acid and thiamine as key factors to consider for species-specific modulation of the metabolic footprint of wine yeasts.

Must protection, sulfites versus bioprotection: A metabolomic study

The reduction of chemical inputs in wine has become one of the main challenges of the wine industry. One of the alternatives to sulfites developed is bioprotection, which consists in using non-Saccharomyces strains to prevent microbial deviation. However, the impact of substituting sulfites by bioprotection on the final wine remains poorly studied. For the first time, we characterized this impact on Chardonnay wine through an integrative approach. Interestingly, physico-chemical analysis did not reveal any difference between both treatments regarding classical oenological parameters. Nevertheless, bioprotection did not seem to provide as much protection against oxidation as sulfites, as observed through phenolic compound analysis. At a deeper level, untargeted metabolomic analyses revealed substantial changes in wine composition according to must treatment. In particular, the specific footprint of each treatment revealed an impact on nitrogen-containing compounds. This observation could be related to modifications in S. cerevisiae metabolism, in particular amino acid biosynthesis and tryptophan metabolism pathways. Thus, the type of must treatment seemed to impact metabolic fluxes of yeast differently, leading to the production of different compounds. For example, we observed glutathione and melatonin, compounds with antioxidant properties, which were enhanced with sulfites, but not with bioprotection. However, despite substantial modifications in wines regarding their chemical composition, the change in must treatment did not seem to impact the sensory profile of wine. This integrative approach has provided relevant new insights on the impact of sulfite substitution by bioprotection on Chardonnay wines.

Bioprotection Efficiency of Metschnikowia Strains in Synthetic Must: Comparative Study and Metabolomic Investigation of the Mechanisms Involved

Three Metschnikowia strains marketed as bioprotection yeasts were studied to compare their antimicrobial effect on a mixture of two Hanseniaspora yeast strains in synthetic must at 12 °C, mimicking pre-fermentative maceration by combining different approaches. The growth of the different strains was monitored, their nitrogen and oxygen requirements were characterised, and their metabolomic footprint in single and co-cultures studied. Only the M. fructicola strain and one M. pulcherrima strains colonised the must and induced the rapid decline of Hanseniaspora. The efficiency of these two strains followed different inhibition kinetics. Furthermore, the initial ratio between Metschnikowia and Hanseniaspora was an important factor to ensure optimal bioprotection. Nutrient consumption kinetics showed that apiculate yeasts competed with Metschnikowia strains for nutrient accessibility. However, this competition did not explain the observed bioprotective effect, because of the considerable nitrogen content remaining on the single and co-cultures. The antagonistic effect of Metschnikowia on Hanseniaspora probably implied another form of amensalism. For the first time, metabolomic analyses of the interaction in a bioprotection context were performed after the pre-fermentative maceration step. A specific footprint of the interaction was observed, showing the strong impact of the interaction on the metabolic modulation of the yeasts, especially on the nitrogen and vitamin pathways.

To be or not to be required: Yeast vitaminic requirements in winemaking

Although vitamins are prime actors in yeast metabolism, the nature and the extent of their requirement in Saccharomyces cerevisiae in winemaking remains little understood. To fill this gap, the evolution of 8 water-soluble vitamins and their diverse vitamers during its alcoholic fermentation in a synthetic must medium was monitored, providing the first evidence of the consumption of vitamers by five commercial S. cerevisiae strains, and highlighting the existence of preferential vitameric sources for its nutrition. The vitamins required by the yeast, B1, B5, and B8, were then identified, and the nature of their requirement characterized, strongly asserting the required trait of B1 for fermentation, B8 for growth, and B5 for both processes. The extent of the requirement for B5, that with the most impact of the three vitamins, was then quantified in three S. cerevisiae strains, resulting in the conclusion that 750 μg.L-1 should prove sufficient to cover the yeast's requirements. This investigation offers the first insight into S. cerevisiae vitaminic requirements for winemaking.

To each their own: Delving into the vitaminic preferences of non-Saccharomyces wine yeasts

Considering the growing interest in non-Saccharomyces wine yeasts, and notably in the context of mixed fermentations with S. cerevisiae, understanding their nutritional behaviors is essential to ensure better management of these fermentations. The vitaminic consumption of three non-Saccharomyces yeasts (Starmerella bacillaris, Metschnikowia pulcherrima and Torulaspora delbrueckii) was investigated during their growth in wine-like conditions, providing initial evidence that they consume different vitamers. The vitamin consumption profiles during their growth highlighted releases of certain vitamers by the yeasts before re-assimilation, strongly suggesting the existence of synthesis pathways. Not only did the essential character of vitamin B1, in particular, appear to be a trait common to these yeasts, since all its vitamers are consumed, this investigation also provided evidence of the existence of species-dependent preferences for their vitaminic sources. These different behaviors were quite striking in certain vitamers, as was observed in nicotinamide: while it was consumed by T. delbrueckii, it was left untouched by S. bacillaris and produced by M. pulcherrima during growth. Furthermore, this offers grounds for further investigation into these yeasts' requirements, and provides the first tool for managing vitamin resources during mixed fermentations with S. cerevisiae, and for preventing nutritive deficiencies from occurring.

An edible coating utilizing Malva sylvestris seed polysaccharide mucilage and postbiotic from Saccharomyces cerevisiae var. boulardii for the preservation of lamb meat

Currently, microbial bioactive substances (postbiotics) are considered a promising tool for achieving customer demand for natural preservatives. This study aimed to investigate the effectiveness of an edible coating developed by Malva sylvestris seed polysaccharide mucilage (MSM) and postbiotics from Saccharomyces cerevisiae var. boulardii ATCC MYA-796 (PSB) for the preservation of lamb meat. PSB were synthesized, and a gas chromatograph connected to a mass spectrometer and a Fourier transform infrared spectrometer were used to determine their chemical components and main functional groups, respectively. The Folin-Ciocalteu and aluminium chloride techniques were utilized to assess the total flavonoid and phenolic levels of PSB. Following that, PSB has been incorporated into the coating mixture, which contains MSM, and its potential radical scavenging and antibacterial activities on lamb meat samples were determined after 10 days of 4 °C storage. PSB contains 2-Methyldecane, 2-Methylpiperidine, phenol, 2,4-bis (1,1-dimethyl ethyl), 5,10-Diethoxy-2,3,7,8- tetrahydro-1H,6H-dipyrrolo[1,2-a:1',2'-d] pyrazine, and Ergotaman-3',6',18-trione, 12'-hydroxy-2'-methyl-5'-(phenylmethyl)-, (5'alpha) as well as various organic acids with significant radical scavenging activity (84.60 ± 0.62 %) and antibacterial action toward Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus, Staphylococcus aureus, and Listeria innocua as foodborne pathogens. The edible PSB-MSM coating effectively reduced microbial growth and increased meat shelf life (> 10 days). When PSB solutions were added to the edible coating, the moisture content, pH value, and hardness of the samples were also more successfully maintained (P < 0.05). The PSB-MSM coating inhibited lipid oxidation in meat samples considerably and diminished the formation of primary as well as secondary oxidation intermediates (P < 0.05). Additionally, when MSM + 10 % PSB edible coating was utilized, the sensory properties of the samples were maintained more well during preservation. As a significance, the use of edible coatings based on PSB and MSM is efficient in decreasing microbiological and chemical degradation in lamb meat during preservation.