Ismail Ku Syahidah Ku, Sakamoto Takatoshi, Hasunuma Tomohisa, Zhao Xin-Qing, Kondo Akihiko
Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe, Japan; School of Bioprocess Engineering, Universiti Malaysia Perlis, Perlis, Malaysia.
Biotechnol J. 2014 Dec;9(12):1519-25. doi: 10.1002/biot.201300553. Epub 2014 Jul 29.
Lignocellulosic biomass is a potential substrate for ethanol production. However, pretreatment of lignocellulosic materials produces inhibitory compounds such as acetic acid, which negatively affect ethanol production by Saccharomyces cerevisiae. Supplementation of the medium with three metal ions (Zn(2+) , Mg(2+) , and Ca(2+) ) increased the tolerance of S. cerevisiae toward acetic acid compared to the absence of the ions. Ethanol production from xylose was most improved (by 34%) when the medium was supplemented with 2 mM Ca(2+) , followed by supplementation with 3.5 mM Mg(2+) (29% improvement), and 180 μM Zn(2+) (26% improvement). Higher ethanol production was linked to high cell viability in the presence of metal ions. Comparative transcriptomics between the supplemented cultures and the control suggested that improved cell viability resulted from the induction of genes controlling the cell wall and membrane. Only one gene, FIT2, was found to be up-regulated in common between the three metal ions. Also up-regulation of HXT1 and TKL1 might enhance xylose consumption in the presence of acetic acid. Thus, the addition of ionic nutrients is a simple and cost-effective method to improve the acetic acid tolerance of S. cerevisiae.
木质纤维素生物质是乙醇生产的潜在底物。然而，木质纤维素材料的预处理会产生抑制性化合物，如乙酸，这会对酿酒酵母的乙醇生产产生负面影响。与不添加离子相比，在培养基中添加三种金属离子（Zn(2+)、Mg(2+)和Ca(2+)）可提高酿酒酵母对乙酸的耐受性。当培养基中添加2 mM Ca(2+)时，木糖的乙醇产量提高最为显著（提高了34%），其次是添加3.5 mM Mg(2+)（提高了29%）和180 μM Zn(2+)（提高了26%）。较高的乙醇产量与金属离子存在下的高细胞活力有关。添加金属离子的培养物与对照之间的比较转录组学表明，细胞活力的提高是由于控制细胞壁和细胞膜的基因的诱导。在三种金属离子之间，仅发现一个基因FIT2上调。HXT1和TKL1的上调也可能会增强在乙酸存在下木糖的消耗。因此，添加离子营养物是提高酿酒酵母对乙酸耐受性的一种简单且经济有效的方法。
