Efficient production of desulfurizing cells with the aid of expert system

An expert system was used to achieve the high production of desulfurizing cells of Rhodococcus erythropolis KA 2-5-1. By adding a proper amount of sulfur containing component with the aid of the expert system, we could avoid excess feeding which resulted in the lowering of desulfurizing activity and starvation which caused serious damage to cell growth. In order to determine the addition amount by the expert system, the data of the amount of chemical elements contained in the cells were used as a reference for comparison with the medium components present. Culture experiments were carried out using a 51 jar fermenter with several kinds of media whose components were determined based on the inferred results with the aid of the expert system. We could restrict the amount of the sulfur component addition so that sulfur was a growth-limiting factor; in contrast, the amounts of other elements were sufficient for growth. As a result, the maximum specific production rate of 2-hydroxy biphenyl (2HBP) and the maximum cell concentration were 20 mmol kg-drycells(-1) h(-1) and of 45 g-drycells l(-1), respectively. At 100 h of cultivation, 1 g/l of dibenzothiophene (DBT) was converted to 2HBP within 20 h, i.e., 10 mmol kg-drycells(-1) h(-1) of specific desulfurization activity, and the specific activity remained stable for a long period in the culture experiment. (C) 2000 Elsevier Science S.A. All rights reserved.