Rajoka M I, Ferhan M, Khalid A M
Industrial Biotechnology Division, National Institute for Biotechnology and Genetic Engineering, Faisalabad, Pakistan.
Lett Appl Microbiol. 2005;40(5):316-21. doi: 10.1111/j.1472-765X.2005.01663.x.
The present investigation deals with the development of thermotolerant mutant strain of yeast for studying enhanced productivity of ethanol from molasses in a fully controlled bioreactor.
The parental culture of Saccharomyces cerevisiae ATCC 26602 was mutated using UV treatment. A single thermotolerant mutant was isolated after extensive screening and optimization, and grown on molasses medium in liquid cultures. The mutant was 1.45-fold improved than its wild parent with respect to ethanol productivity (7.2 g l-1 h-1), product yield (0.44 g ethanol g-1 substrate utilized) and specific ethanol yield (19.0 g ethanol g-1 cells). The improved ethanol productivity was directly correlated with titres of intracellular and extracellular invertase activities. The mutant supported higher volumetric and product yield of ethanol, significantly (P<or=0.05) higher than the parental and other strains. The mutated cultures produced 1.8- and 2.6-fold more extracellular and intracellular invertase productivity, respectively, than that produced by its wild parent at 40 degrees C. Thermodynamic studies revealed that the cell system exerted protection against thermal inactivation during formation of products.
A mutant derivative of Sacchromyces cerevisiae with improved productivity of ethanol and invertases has been obtained, which showed concomitant improvement in thermostability of endogenous metabolism for formation of both ethanol and invertases.
The results of the present study are of commercial value as the mutant can be used for ethanol production in parts of Pakistan where the temperature may go up to 40 degrees C in April. Ethanol product yield coefficient and volumetric productivity, revealed the hyper-productivity of ethanol from molasses at 40 degrees C, which is not appropriate for wild organism.
本研究旨在开发一种耐热酵母突变菌株，用于在完全受控的生物反应器中研究提高糖蜜乙醇产量。
采用紫外线处理酿酒酵母ATCC 26602的亲本培养物。经过广泛筛选和优化后分离出一个耐热突变体，并在糖蜜培养基中进行液体培养。该突变体在乙醇产量（7.2 g l-1 h-1）、产物得率（0.44 g乙醇 g-1利用底物）和比乙醇产量（19.0 g乙醇 g-1细胞）方面比其野生亲本提高了1.45倍。乙醇产量的提高与细胞内和细胞外转化酶活性的滴度直接相关。该突变体支持更高的乙醇体积产量和产物得率，显著高于亲本和其他菌株（P≤0.05）。在40℃下，突变培养物产生的细胞外和细胞内转化酶产量分别比其野生亲本多1.8倍和2.6倍。热力学研究表明，细胞系统在产物形成过程中对热失活具有保护作用。
获得了一种酿酒酵母突变衍生物，其乙醇和转化酶产量提高，同时乙醇和转化酶形成的内源性代谢热稳定性也有所提高。
本研究结果具有商业价值，因为该突变体可用于巴基斯坦部分地区的乙醇生产，那里4月份温度可能高达40℃。乙醇产物得率系数和体积生产力表明，在40℃下从糖蜜中生产乙醇具有高产率，这对野生生物来说是不合适的。
