Degradation of Salicylic Acid by Free and Immobilized Cells of Pseudomonas sp. Strain NGK1

A Pseudomonas sp. strain NGK1 (NCIM 5120) capable of utilizing salicylate was immobilized in alginate and polyurethane foam (PUF). The degradation rate of salicylate by freely suspended cells was compared with the degradation rate by immobilized cells. In an initial 20 and 40 mM salicylate, free cells ($2{\times}10^{11}\;cfu\;ml^{-1}$) degraded to 16 and 14 mM, alginate-entrapped cells degraded to 18 and 26 mM, and PUF-entrapped cells degraded to 20 and 32 mM salicylate, respectively, in batch cultures. The alginate-and PUF-entrapped cells were used in repeated batch and continuous culture systems. The efficiency of both the immobilized systems f3r the degradation of salicylate was compared. It has been observed that the PUF-entrapped cells could be reused for more than 20 cycles whereas alginate-entrapped cells could be reused for a maximum of only 12 cycles, after which a decrease in degradation rat was observed with the initial 20 and 40 mM salicylate. The continuous degradation of sallcylate by freely suspended cells showed a negligible degradation rate of salicylate when compared with immobilized cells. With the immobilized cells in both alginate and polyurethane foam, the degradation rate increased with an increase in the dilution rate up to $2\;h^{-1}$ for 20 mM, and $1.5\;h^{-1}$ for 40 mM salicylate. The results revealed that PUF-entrapped cells were more efficient for the degradation of salicylate than alginate-entrapped cells and freely suspended cells.