Department of Animal Sciences and Ohio State Agricultural Research and Development Center (OARDC), The Ohio State University, 305 Gerlaugh Hall, 1680 Madison Avenue, Wooster, OH 44691, USA.
Appl Microbiol Biotechnol. 2010 Feb;85(6):1697-712. doi: 10.1007/s00253-009-2390-0. Epub 2009 Dec 22.
Anaerobic bacteria such as the solventogenic clostridia can ferment a wide range of carbon sources (e.g., glucose, galactose, cellobiose, mannose, xylose, and arabinose) to produce carboxylic acids (acetic and butyric) and solvents such as acetone, butanol, and ethanol (ABE). The fermentation process typically proceeds in two phases (acidogenic and solventogenic) in a batch mode. Poor solvent resistance by the solventogenic clostridia and other fermenting microorganisms is a major limiting factor in the profitability of ABE production by fermentation. The toxic effect of solvents, especially butanol, limits the concentration of these solvents in the fermentation broth, limiting solvent yields and adding to the cost of solvent recovery from dilute solutions. The accepted dogma is that toxicity in the ABE fermentation is due to chaotropic effects of butanol on the cell membranes of the fermenting microorganisms, which poses a challenge for the biotechnological whole-cell bio-production of butanol. This mini-review is focused on (1) the effects of solvents on inhibition of cell metabolism (nutrient transport, ion transport, and energy metabolism); (2) cell membrane fluidity, death, and solvent tolerance associated with the ability of cells to tolerate high concentrations of solvents without significant loss of cell function; and (3) strategies for overcoming poor solvent resistance in acetone and butanol-producing microorganisms.
厌氧细菌，如产溶剂梭菌，可以发酵多种碳源（例如葡萄糖、半乳糖、纤维二糖、甘露糖、木糖和阿拉伯糖）生产羧酸（乙酸和丁酸）和溶剂，如丙酮、丁醇和乙醇（ABE）。发酵过程通常以分批模式在两个阶段（产酸和产溶剂）中进行。由于产溶剂梭菌和其他发酵微生物对溶剂的耐受性差，这是发酵生产 ABE 的盈利能力的主要限制因素。溶剂的毒性作用，特别是丁醇，限制了发酵液中这些溶剂的浓度，限制了溶剂的产率，并增加了从稀溶液中回收溶剂的成本。公认的观点是，ABE 发酵中的毒性是由于丁醇对发酵微生物细胞膜的离液效应引起的，这对生物技术全细胞生物生产丁醇提出了挑战。本综述主要集中在以下三个方面：（1）溶剂对细胞代谢（营养物质运输、离子运输和能量代谢）抑制的影响；（2）细胞膜流动性、死亡和溶剂耐受性与细胞耐受高浓度溶剂而不显著丧失细胞功能的能力相关；（3）克服产丙酮和丁醇微生物对溶剂耐受性差的策略。
