Duncan James D, Setati Mathabatha E, Divol Benoit
South African Grape and Wine Research Institute, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
FEMS Yeast Res. 2024 Jan 9;24. doi: 10.1093/femsyr/foae015.
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.
厌氧酒精发酵，尤其是在高糖环境中，给酵母带来了代谢挑战。包括酿酒酵母在内的巴斯德效应阳性酵母即使在有氧的情况下也更喜欢发酵。这些酵母依赖于内部的NAD⁺循环及其前体烟酸（维生素B3）的细胞外同化，而不是从头合成NAD⁺。令人惊讶的是，即使在酿酒酵母中，烟酸同化的特征也很不明确。本研究阐明了类似葡萄汁发酵过程中烟酸摄取的时间及其对NAD(H)水平、NAD⁺/NADH比率和产生的代谢物的影响。细胞外烟酸的完全摄取发生在指数中期之前，此后少量的维生素B3被重新输出到培养基中。烟酸水平次优与发酵速度减慢和生物量减少相关，破坏了氧化还原平衡并阻碍了NAD⁺的再生，从而影响代谢物的产生。代谢结果随烟酸浓度而变化，将NAD⁺的可用性与发酵效率联系起来。提出了一个模型，包括快速摄取烟酸、在细胞增殖过程中积累以及在有限的维生素B3输出情况下进行循环利用。这项研究增进了对类似葡萄汁发酵过程中烟酸摄取动态的理解。这些见解有助于推进酵母代谢研究，并对生物技术实践和酿酒工业的改进具有深远意义。
