Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755.
Appl Environ Microbiol. 1989 Dec;55(12):3131-9. doi: 10.1128/aem.55.12.3131-3139.1989.
Fermentation of dilute-acid-pretreated mixed hardwood and Avicel by Clostridium thermocellum was compared in batch and continuous cultures. Maximum specific growth rates per hour obtained on cellulosic substrates were 0.1 in batch culture and >0.13 in continuous culture. Cell yields (grams of cells per gram of substrate) in batch culture were 0.17 for pretreated wood and 0.15 for Avicel. Ethanol and acetate were the main products observed under all conditions. Ethanol:acetate ratios (in grams) were approximately 1.8:1 in batch culture and generally slightly less than 1:1 in continuous culture. Utilization of cellulosic substrates was essentially complete in batch culture. A prolonged lag phase was initially observed in batch culture on pretreated wood; the length of the lag phase could be shortened by addition of cell-free spent medium. In continuous culture with approximately 5 g of glucose equivalent per liter in the feed, substrate conversion relative to theoretical ranged from 0.86 at a dilution rate (D) of 0.05/h to 0.48 at a D of 0.167/h for Avicel and from 0.75 at a D of 0.05/h to 0.43 at a D of 0.11/h for pretreated wood. At feed concentrations of <4.5 g of glucose equivalent per liter, conversion of pretreated wood was 80 to 90% at D = 0.083/h. Lower conversion was obtained at higher feed substrate concentrations, consistent with a limiting factor other than cellulose. Free Avicelase activities of 12 to 84 mU/ml were observed, with activity increasing in this order: batch cellobiose, batch pretreated wood < batch Avicel, continuous pretreated wood < continuous Avicel. Free cellulase activity was higher at increasing extents of substrate utilization for both pretreated wood and Avicel under all conditions tested. The results indicate that fermentation parameters, with the exception of free cellulase activity, are essentially the same for pretreated mixed hardwood and Avicel under a variety of conditions. Hydrolysis yields obtained with C. thermocellum cellulase acting either in vitro or in vivo were comparable to those previously reported for Trichoderma reesei on the same substrates.
用嗜热梭菌在分批和连续培养中比较了稀酸预处理混合硬木和 Avicel 的发酵。在纤维素基质上每小时获得的最大比生长速率在分批培养中为 0.1，在连续培养中大于 0.13。在分批培养中，预处理木材的细胞产率（每克基质的细胞克数）为 0.17，Avicel 为 0.15。在所有条件下，观察到的主要产物都是乙醇和乙酸。在分批培养中，乙醇：乙酸比（克）约为 1.8:1，而在连续培养中通常略小于 1:1。在分批培养中，纤维素基质的利用率基本完全。在预处理木材的分批培养中最初观察到一个延长的迟滞期；通过添加无细胞的废培养基，可以缩短迟滞期的长度。在进料中约有 5 克葡萄糖当量/升的连续培养中，相对于理论值，基质转化率在稀释率（D）为 0.05/h 时从 0.86 到 D 为 0.167/h 时为 0.48 ，Avicel 为 0.75，对于预处理木材，D 为 0.11/h 时为 0.43。在进料浓度<4.5 克葡萄糖当量/升时，D = 0.083/h 时，预处理木材的转化率为 80%至 90%。在较高的进料基质浓度下，转化率较低，与纤维素以外的限制因素一致。观察到游离的纤维二糖酶活性为 12 至 84 mU/ml，活性顺序为：分批纤维二糖、分批预处理木材<分批 Avicel、连续预处理木材<连续 Avicel。在所有测试条件下，随着预处理木材和 Avicel 基质利用率的增加，游离纤维素酶活性均升高。结果表明，在各种条件下，除游离纤维素酶活性外，预处理混合硬木和 Avicel 的发酵参数基本相同。用嗜热梭菌纤维素酶在体外或体内作用获得的水解产物与在相同基质上用里氏木霉获得的水解产物相当。
