Degradation of dimethyl sulfoxide by the immobilized cells of Hyphomicrobium denitrificans WU-K217

Dimethyl sulfoxide (DMSO)-degrading ability of Hyphomicrobium denitrificans WU-K217 immobilized by entrapment with calcium-alginate gel was examined. The immobilized cells with the cell density of 0.46 mg-dry weight ml^-1 degraded 0.64 mM (50 mgl^-1) DMSO within 180 min at a temperature range from 20 to 35 °C, similarly to the freely-suspended cells. At 40 °C, the immobilized cells completely degraded 0.64 mM DMSO within 240 min, although the freely-suspended cells could not degrade it under the same condition. The half-life of DMSO-degradation activity for the immobilized cells stored at 30 °C was 96 h and it was extended to more than 240 h by the storage at 4 °C. However, in the case of the freely-suspended cells, the half-life was shorter than 48 h even by the storage at 4 °C. These results indicated that the immobilized WU-K217 cells had high thermostability and storage stability compared to those of the freely-suspended cells. Considering these characteristics, we performed the repeated DMSO degradation by reuse of the immobilized cells. As a result, even at the tenth reaction, the immobilized cells maintained 90% of DMSO-degradation rate of that at the first reaction. These results suggested that the immobilized cells of WU-K217 might be applicable to a wastewater-treatment system for the removal of DMSO.