Chen C, Dale M C, Okos M R
Department of Agricultural Engineering, Purdue University, W. Lafayette, Indiana 47907, USA.
Biotechnol Bioeng. 1990 Dec 5;36(10):993-1001. doi: 10.1002/bit.260361004.
The effect of reduced nutritional levels (particularly nitrogen source) for immobilized K. fragilis type yeast were studied using a trickle flow, "differential" plug flow type reactor with cells immobilized by adsorption onto an absorbant packing matrix. Minimizing nutrient levels in a feed stream to an immobilized cell reactor (ICR) might have the benefits of reducing cell growth and clogging problems in the ICR, reducing feed preparation costs, as well as reducing effluent disposal costs. In this study step changes in test feed medium nutrient compositions were introduced to the ICR, followed by a return to a basal medium. Gas evolution rates were monitored and logged on a continuous basis, and effluent cell density was used as an indicator of cell growth rate of the immobilized cell mass. Startup of the reactor using a YEP medium showed a rapid buildup of cells in the reactor during the initial 110 h operation. The population density then stabilized at 1.6 x 10(11) cells/g sponge. A defined medium containing a complex mix of essential nutrients with an inorganic nitrogen source (ammonium sulfate) was able to maintain 90% of the productivity in the ICR as compared to the YEP medium, but proved unable to promote growth of the immobilized cell mass during startup. Experiments on reduced ammonium sulfate in the defined medium, and reduced yeast extract and peptone in YEP medium indicated that stable productivity could be maintained for extended periods (80 h) in the complete absence of any nutrients besides a few salts (potassium phosphate and magnesium sulfate). It was found that productivity rates dropped by 35-65% from maximal values as nitrogenous nutrients were eliminated from the test mediums, while growth rates (as determined by shed cell density from the reactor) dropped by 75-95%. Thus, nutritional deficiencies largely decoupled growth and productivity of the immobilized yeast which suggests productivity is both growth- and non-growth-associated for the immobilized cells. A yeast extract concentration of 0.375 g/L with or without 1 g/L ammonium sulfate was determined to be the minimum level which gave a sustained increase in productivity rates as compared to the nutritionally deficient salt medium. This represents a 94% reduction in complex nitrogenous nutrient levels compared to standard YEP batch medium (3 g/L YE and 3.5 g/L peptone).
使用滴流“差动”活塞流型反应器，研究了营养水平降低（特别是氮源）对固定化脆壁克鲁维酵母型酵母的影响，该反应器中的细胞通过吸附到吸收性填充基质上进行固定。将固定化细胞反应器（ICR）进料流中的营养水平降至最低，可能具有减少ICR中的细胞生长和堵塞问题、降低进料制备成本以及降低废水处理成本的好处。在本研究中，将测试进料培养基营养成分的阶跃变化引入ICR，然后恢复到基础培养基。连续监测并记录气体逸出速率，并将流出物细胞密度用作固定化细胞团生长速率的指标。使用YEP培养基启动反应器时，在最初110小时的运行期间，反应器中的细胞迅速积累。然后种群密度稳定在1.6×10¹¹个细胞/克海绵。与YEP培养基相比，含有必需营养素与无机氮源（硫酸铵）的复杂混合物的限定培养基能够在ICR中维持90%的生产力，但在启动期间无法促进固定化细胞团的生长。在限定培养基中降低硫酸铵以及在YEP培养基中降低酵母提取物和蛋白胨的实验表明，除了几种盐（磷酸钾和硫酸镁）外，在完全没有任何营养素的情况下，生产力可以长时间（80小时）维持稳定。结果发现，当从测试培养基中去除含氮营养素时，生产力速率从最大值下降了35 - 65%，而生长速率（由反应器中脱落的细胞密度确定）下降了75 - 95%。因此，营养缺乏在很大程度上使固定化酵母的生长和生产力脱钩，这表明生产力与固定化细胞的生长和非生长相关。与营养缺乏的盐培养基相比，确定0.375克/升的酵母提取物浓度（无论有无1克/升硫酸铵）是使生产力速率持续增加的最低水平。与标准YEP分批培养基（3克/升YE和3.5克/升蛋白胨）相比，这意味着复杂含氮营养素水平降低了94%。
