Moon S H, Parulekar S J
Department of Chemical Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, USA.
Biotechnol Bioeng. 1993 Jan 5;41(1):43-54. doi: 10.1002/bit.260410107.
Invariance of culture conditions in steady state continuous cultures make these a very valuable tool to study the influence of various culture parameters on cell growth and synthesis of primary and secondary metabolites. The result of a parametric study on production of protease in continuous suspension cultures of Bacillus firmus NRS 783 are reported in this article. This strain is a superior producer of an alkaline protease with major application in the detergent industry. The parameters investigated include dilution rate and concentrations of yeast extract, ammonium, and inorganic phosphate in the bioreactor feed, glucose being the principal carbon source in all experiments. The regulatory effects of the key culture parameters on cell growth, synthesis and secretion of protease, and production of acetic acid are investigated. The relations among the specific cell growth rate, specific utilization rates of the principal carbon, nitrogen, and phosphorous sources, and specific production rates of two nonbiomass products, viz., acetic acid and protease, are examined, and the effects of the manipulated culture parameters on these relations, specific protease activity, and yields of cell mass, protease, and acetic acid on the basis of the principal carbon, nitrogen, and phosphorous sources are studied. An increase in dilution rate led to increases in specific utilization rates of the principal carbon, nitrogen, and phosphorous sources and specific production rates of acetic acid and protease and decreases in bulk activities/concentrations of the three products (acetic acid, cell mass, and protease). As a result, the productivities of the three species were maximized at an intermediate dilution rate. Increased supply of yeast extract (a rich source of amino acids, proteins, and vitamins, besides being an additional source of carbon, nitrogen, and phosphorus) promoted cell mass formation but reduced protease production per unit cell mass. Increased supply of nitrogen and phosphorous sources stimulated protease synthesis up to certain threshold levels and repressed the enzyme synthesis beyond the threshold levels. With increased supply of the nitrogen source, the phosphorous source was more efficiently utilized for cell growth and protease synthesis. Stable maintenance of continuous cultures of B. firmus over prolonged period is demonstrated in this study.
稳态连续培养中培养条件的不变性使这些培养成为研究各种培养参数对细胞生长以及初级和次级代谢产物合成影响的非常有价值的工具。本文报道了对坚强芽孢杆菌NRS 783连续悬浮培养中蛋白酶生产的参数研究结果。该菌株是一种碱性蛋白酶的高产菌株，在洗涤剂工业中有主要应用。研究的参数包括稀释率以及生物反应器进料中酵母提取物、铵和无机磷酸盐的浓度，在所有实验中葡萄糖都是主要碳源。研究了关键培养参数对细胞生长、蛋白酶的合成与分泌以及乙酸生产的调节作用。考察了比细胞生长速率、主要碳源、氮源和磷源的比利用率以及两种非生物质产物即乙酸和蛋白酶的比生产率之间的关系，并研究了调控的培养参数对这些关系、比蛋白酶活性以及基于主要碳源、氮源和磷源的细胞质量、蛋白酶和乙酸产量的影响。稀释率的增加导致主要碳源、氮源和磷源的比利用率以及乙酸和蛋白酶的比生产率增加，同时三种产物（乙酸、细胞质量和蛋白酶）的总体活性/浓度降低。结果，三种物质的生产率在中间稀释率下达到最大值。增加酵母提取物的供应（除了作为碳、氮和磷的额外来源外，还是氨基酸、蛋白质和维生素的丰富来源）促进了细胞质量的形成，但降低了单位细胞质量的蛋白酶产量。增加氮源和磷源的供应在一定阈值水平之前刺激蛋白酶合成，而在阈值水平之后则抑制酶的合成。随着氮源供应的增加，磷源更有效地用于细胞生长和蛋白酶合成。本研究证明了坚强芽孢杆菌连续培养能够长期稳定维持。
