State Key Laboratory of Pulp and Paper Engineering, College of Light Industry and Food Sciences, South China University of Technology, 381 Wushan Rd,,Tianhe District, Guangzhou 510640, China.
Biotechnol Biofuels. 2012 Jan 19;5:4. doi: 10.1186/1754-6834-5-4.
Microbial lipids have drawn increasing attention in recent years as promising raw materials for biodiesel production, and the use of lignocellulosic hydrolysates as carbon sources seems to be a feasible strategy for cost-effective lipid fermentation with oleaginous microorganisms on a large scale. During the hydrolysis of lignocellulosic materials with dilute acid, however, various kinds of inhibitors, especially large amounts of organic acids, will be produced, which substantially decrease the fermentability of lignocellulosic hydrolysates. To overcome the inhibitory effects of organic acids, it is critical to understand their impact on the growth and lipid accumulation of oleaginous microorganisms.
In our present work, we investigated for the first time the effect of ten representative organic acids in lignocellulosic hydrolysates on the growth and lipid accumulation of oleaginous yeast Trichosporon fermentans cells. In contrast to previous reports, we found that the toxicity of the organic acids to the cells was not directly related to their hydrophobicity. It is worth noting that most organic acids tested were less toxic than aldehydes to the cells, and some could even stimulate the growth and lipid accumulation at a low concentration. Unlike aldehydes, most binary combinations of organic acids exerted no synergistic inhibitory effects on lipid production. The presence of organic acids decelerated the consumption of glucose, whereas it influenced the utilization of xylose in a different and complicated way. In addition, all the organic acids tested, except furoic acid, inhibited the malic activity of T. fermentans. Furthermore, the inhibition of organic acids on cell growth was dependent more on inoculum size, temperature and initial pH than on lipid content.
This work provides some meaningful information about the effect of organic acid in lignocellulosic hydrolysates on the lipid production of oleaginous yeast, which is helpful for optimization of biomass hydrolysis processes, detoxified pretreatment of hydrolysates and lipid production using lignocellulosic materials.
近年来，微生物油脂作为生物柴油生产的有前途的原料引起了越来越多的关注，利用木质纤维素水解物作为碳源似乎是一种可行的策略，可以用产油微生物在大规模上进行经济高效的油脂发酵。然而，在使用稀酸水解木质纤维素材料时，会产生各种抑制剂，特别是大量的有机酸，这会大大降低木质纤维素水解物的发酵性能。为了克服有机酸的抑制作用，了解它们对产油微生物的生长和油脂积累的影响至关重要。
在我们目前的工作中，我们首次研究了木质纤维素水解物中的十种代表性有机酸对产油酵母 Trichosporon fermentans 细胞生长和油脂积累的影响。与以前的报告不同，我们发现有机酸对细胞的毒性与它们的疏水性无关。值得注意的是，与醛类相比，测试的大多数有机酸对细胞的毒性较小，并且在低浓度下甚至可以刺激生长和油脂积累。与醛类不同，大多数有机酸的二元组合对油脂生产没有协同抑制作用。有机酸的存在会减缓葡萄糖的消耗，而对木糖的利用则以不同且复杂的方式产生影响。此外，除了糠酸外，测试的所有有机酸都抑制了 T. fermentans 的苹果酸活性。此外，有机酸对细胞生长的抑制作用更多地取决于接种量、温度和初始 pH 值，而不是脂质含量。
这项工作提供了一些关于木质纤维素水解物中有机酸对产油酵母油脂生产影响的有意义的信息，这有助于优化生物质水解过程、水解物的解毒预处理以及利用木质纤维素材料进行油脂生产。
