Data_Sheet_2_Extreme Osmotolerance and Halotolerance in Food-Relevant Yeasts and the Role of Glycerol-Dependent Cell Individuality.PDF

Osmotolerance or halotolerance are used to describe resistance to sugars and salt, or only salt, respectively. Here, a comprehensive screen of more than 600 different yeast isolates revealed that osmosensitive species were equally affected by NaCl and glucose. However, the relative toxicity of salt became increasingly prominent in more osmoresistant species. We confirmed that growth inhibition by glucose in a laboratory strain of Saccharomyces cerevisiae occurred at a lower water activity (Aw) than by salt (NaCl), and pre-growth in high levels of glucose or salt gave enhanced cross-resistance to either. Salt toxicity was largely due to osmotic stress but with an additive enhancement due to effects of the relevant cation. Almost all of the yeast isolates from the screen were also noted to exhibit hetero-resistance to both salt and sugar, whereby high concentrations restricted growth to a small minority of cells within the clonal populations. Rare resistant colonies required growth for up to 28 days to become visible. This cell individuality was more marked with salt than sugar, a possible further reflection of the ion toxicity effect. In both cases, heteroresistance in S. cerevisiae was strikingly dependent on the GPD1 gene product, important for glycerol synthesis. In contrast, a tps1Δ deletant impaired for trehalose showed altered MIC but no change in heteroresistance. Effects on heteroresistance were evident in chronic (but not acute) salt or glucose stress, particularly relevant to growth on low Aw foods. The study reports diverse osmotolerance and halotolerance phenotypes and heteroresistance across an extensive panel of yeast isolates, and indicates that Gpd1-dependent glycerol synthesis is a key determinant enabling growth of rare yeast subpopulations at low Aw, brought about by glucose and in particular salt.

耐渗透压性（osmotolerance）与耐盐性（halotolerance）分别用于表征对糖与盐的耐受能力，以及仅对盐的耐受能力。本研究针对600余株不同酵母分离株开展全面筛选，结果显示渗透压敏感菌种受氯化钠（NaCl）与葡萄糖的抑制效果相当。但在高耐渗透压菌种中，盐类的相对毒性愈发突出。我们证实，酿酒酵母（Saccharomyces cerevisiae）实验室菌株的葡萄糖诱导生长抑制所需的水分活度（water activity, Aw）低于氯化钠；且在高浓度葡萄糖或盐类中预培养，可增强对另一类胁迫的交叉抗性。盐类的毒性主要源于渗透胁迫，同时受对应阳离子的作用产生附加增强效应。本次筛选获得的几乎所有酵母分离株均表现出对盐与糖的异抗性（heteroresistance）：即高浓度胁迫仅能抑制克隆种群中的绝大多数细胞，仅少数细胞可存活；罕见的抗性菌落需长达28天的培养方可肉眼观测到。这种细胞个体差异在盐胁迫下较糖胁迫更为显著，这或许进一步反映了离子毒性的作用机制。两类胁迫下，酿酒酵母的异抗性均显著依赖于参与甘油合成的GPD1基因产物。与之相反，海藻糖合成受损的tps1Δ缺失突变体的最小抑菌浓度（MIC）发生改变，但异抗性未受影响。该异抗性效应仅在慢性（而非急性）盐或葡萄糖胁迫中显现，这与低水分活度食品上的微生物生长情况高度相关。本研究报道了针对大范围酵母分离株的多样化耐渗透压与耐盐表型及异抗性特征，并指出依赖Gpd1的甘油合成是使少数酵母亚群在葡萄糖（尤其是盐类）所致的低水分活度环境中生长的关键决定因素。