Nakayama Shunichi, Morita Tomotake, Negishi Hideyuki, Ikegami Toru, Sakaki Keiji, Kitamoto Dai
Research Institute for Innovation in Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central, Higashi, Tsukuba, Ibaraki, Japan.
FEMS Yeast Res. 2008 Aug;8(5):706-14. doi: 10.1111/j.1567-1364.2008.00384.x. Epub 2008 Apr 9.
The development of fermentative yeasts secreting no organic acids is highly desirable for ethanol production coupled with membrane separation processes, because the acidic byproduct, succinic acid, significantly inhibits the membrane permeation of ethanol. Of the Pichia and Candida yeasts tested, Candida krusei IA-1 showed the highest ethanol productivity [55 g L(-1) day(-1) from 150 g L(-1) (w/v) of glucose], comparable to the strains of Saccharomyces cerevisiae, and produced much less of the acid (0.6 g L(-1) day(-1)) than the Saccharomyces strains (1.5-1.8 g L(-1) day(-1)) under semi-aerobic conditions. Interestingly, under aerobic conditions, strain IA-1 showed no production of the acid. Stain IA-1 exhibited a good assimilation of the acid, while S. cerevisiae NBRC 0216 showed no assimilation. The activity of succinate dehydrogenase (SDH) in strain IA-1 was 37.5 mU mg(-1), and 7.8-fold higher than that in S. cerevisiae strain NBRC 0216. More significantly, SDH1 was abundantly transcribed in strain IA-1, different from that in strain NBRC 0216, regardless of the culture conditions. From these results, C. krusei IA-1 efficiently takes up succinic acid and metabolizes it in the Krebs cycle, producing an extremely low level of byproducts in the culture medium. Therefore, C. krusei is not only a promising alternative to S. cerevisiae but also a suitable model for metabolic engineering of S. cerevisiae.
对于结合膜分离工艺的乙醇生产而言，开发不分泌有机酸的发酵酵母是非常必要的，因为酸性副产物琥珀酸会显著抑制乙醇的膜渗透。在所测试的毕赤酵母和假丝酵母中，克鲁维假丝酵母IA-1表现出最高的乙醇生产率[以150 g L⁻¹（w/v）葡萄糖为原料，乙醇生产率为55 g L⁻¹ 天⁻¹]，与酿酒酵母菌株相当，并且在半好氧条件下产生的酸（0.6 g L⁻¹ 天⁻¹）比酿酒酵母菌株（1.5 - 1.8 g L⁻¹ 天⁻¹）少得多。有趣的是，在好氧条件下，IA-1菌株不产生酸。IA-1菌株对酸具有良好的同化作用，而酿酒酵母NBRC 0216则没有同化作用。IA-1菌株中琥珀酸脱氢酶（SDH）的活性为37.5 mU mg⁻¹，比酿酒酵母菌株NBRC 0216高7.8倍。更显著的是，无论培养条件如何，SDH1在IA-1菌株中大量转录，这与NBRC 0216菌株不同。基于这些结果，克鲁维假丝酵母IA-1能有效地摄取琥珀酸并在三羧酸循环中代谢它，在培养基中产生极低水平的副产物。因此，克鲁维假丝酵母不仅是酿酒酵母的一个有前途的替代菌株，也是酿酒酵母代谢工程的一个合适模型。
