Department of Agronomy Food Natural resources Animals and Environment (DAFNAE), University of Padova, Agripolis, Viale dell'Università 16, 35020 Legnaro, Italy.
Biotechnol Biofuels. 2013 Nov 29;6(1):168. doi: 10.1186/1754-6834-6-168.
Robust yeasts with high inhibitor, temperature, and osmotic tolerance remain a crucial requirement for the sustainable production of lignocellulosic bioethanol. These stress factors are known to severely hinder culture growth and fermentation performance.
Grape marc was selected as an extreme environment to search for innately robust yeasts because of its limited nutrients, exposure to solar radiation, temperature fluctuations, weak acid and ethanol content. Forty newly isolated Saccharomyces cerevisiae strains gave high ethanol yields at 40°C when inoculated in minimal media at high sugar concentrations of up to 200 g/l glucose. In addition, the isolates displayed distinct inhibitor tolerance in defined broth supplemented with increasing levels of single inhibitors or with a cocktail containing several inhibitory compounds. Both the fermentation ability and inhibitor resistance of these strains were greater than those of established industrial and commercial S. cerevisiae yeasts used as control strains in this study. Liquor from steam-pretreated sugarcane bagasse was used as a key selective condition during the isolation of robust yeasts for industrial ethanol production, thus simulating the industrial environment. The isolate Fm17 produced the highest ethanol concentration (43.4 g/l) from the hydrolysate, despite relatively high concentrations of weak acids, furans, and phenolics. This strain also exhibited a significantly greater conversion rate of inhibitory furaldehydes compared with the reference strain S. cerevisiae 27P. To our knowledge, this is the first report describing a strain of S. cerevisiae able to produce an ethanol yield equal to 89% of theoretical maximum yield in the presence of high concentrations of inhibitors from sugarcane bagasse.
This study showed that yeasts with high tolerance to multiple stress factors can be obtained from unconventional ecological niches. Grape marc appeared to be an unexplored and promising substrate for the isolation of S. cerevisiae strains showing enhanced inhibitor, temperature, and osmotic tolerance compared with established industrial strains. This integrated approach of selecting multiple resistant yeasts from a single source demonstrates the potential of obtaining yeasts that are able to withstand a number of fermentation-related stresses. The yeast strains isolated and selected in this study represent strong candidates for bioethanol production from lignocellulosic hydrolysates.
具有高抑制剂、温度和渗透压耐受性的健壮酵母仍然是木质纤维素生物乙醇可持续生产的关键要求。这些应激因素已知严重阻碍了培养物的生长和发酵性能。
由于葡萄渣的营养有限、暴露于太阳辐射、温度波动、弱酸性和乙醇含量，因此选择葡萄渣作为极端环境来寻找固有的健壮酵母。当在高糖浓度（高达 200g/l 葡萄糖）的最小培养基中接种时，40 株新分离的酿酒酵母菌株在 40°C 下产生了高乙醇产量。此外，这些分离株在补充了不同浓度的单一抑制剂或含有几种抑制化合物的鸡尾酒的限定培养基中表现出明显的抑制剂耐受性。与作为本研究对照菌株的已建立的工业和商业酿酒酵母相比，这些菌株的发酵能力和抑制剂抗性都更大。在分离用于工业乙醇生产的健壮酵母时，使用蒸汽预处理的甘蔗渣酒糟作为关键选择性条件，从而模拟了工业环境。尽管存在相对较高浓度的弱酸、呋喃和酚类物质，分离株 Fm17 仍从水解物中产生了最高的乙醇浓度（43.4g/l）。该菌株还表现出比参考菌株酿酒酵母 27P 更高的抑制性糠醛转化率。据我们所知，这是首次报道能够在高浓度抑制剂存在下从甘蔗渣中产生等于 89%理论最大产量的乙醇的酿酒酵母菌株。
本研究表明，可以从非常规生态位获得对多种应激因素具有高耐受性的酵母。与已建立的工业菌株相比，葡萄渣似乎是一种未被探索且有前途的酿酒酵母菌株的分离来源，具有增强的抑制剂、温度和渗透压耐受性。这种从单一来源选择多种抗性酵母的综合方法表明，获得能够耐受多种发酵相关应激的酵母是有可能的。本研究中分离和选择的酵母菌株是木质纤维素水解物生物乙醇生产的有力候选者。
