Characterization of bioconversion of fumarate to succinate by alginate immobilized Enterococcus faecalis RKY1

In this study, the immobilization characteristics of Enterococcus faecalis RKY1 for succinate production were examined. At first, three natural polymers--agar, kappa-carrageenan, and sodium alginate--were tried as immobilizing matrices. Among these, sodium alginate was selected as the best gel for immobilization of E. faecalis RKY1. Efficient conditions for immobilization were established to be with a 2% (w/v) sodium alginate solution and 2-mm-diameter bead. The bioconversion characteristics of the immobilized cells at various pH values and temperatures were examined and compared with those of free cells. The optimum pH and temperature of the immobilized cells were the same as for free cells, 7.0 and 38 degrees C respectively, but the conversion ratio was higher by immobilization for all the other pH and temperature conditions tested. When the seed volume of the immobilized cells was adjusted to 10% (v/v), 30 g/L of fumarate was completely converted to succinate (0.973 g/g conversion ratio) after 12 h. In addition, the immobilized cells maintained a conversion ratio of >0.95 g/g during 4 wk of storage at 4 degrees C in a 2% (w/v) CaCl2 solution. In repetitive bioconversion experiments, the activity of the immobilized cells decreased linearly according to the number of times of reuse.