Immobilization of a recombinant Escherichia coli producing a thermostable α-l-rhamnosidase: Creation of a bioreactor for hydrolyses of naringin

An α-l-rhamnosidase (E.C. 3.2.1.40) from a newly discovered thermophilic bacterium was expressed in Escherichia coli BL21 DE3 pRIL cells. The cells were immobilized in Ca2+-alginate beads. The temperature of 50 °C used in reactions, appeared to be sufficient for making the mesophilic strain porous enough for the substrate to access the cloned thermostable enzyme. Pretreatment of cells with heat or lysozyme prior to bead formation did not improve the results. The best cell concentration (w/w) for bead preparation was found to be 0.0192 g ml−1 and stability of beads increased if CaCl2 concentration in buffers and substrate was kept at 50 mM. In a 60 min assay, the optimal pH of the entrapped cells was found to be 7.8 and the optimal temperature 60 °C. By packing the beads in a column, a bioreactor for production of l-rhamnose from naringin was created. Full degradation of 7.9 mM naringin could be reached by running the reactor at 1 ml min−1 at 50 °C. The optimal running temperature of the reactor was found to be 50 °C and the reactor was fully stable over 3 days at that temperature. On the fourth day, substrate degradation capacity had decreased by 10–15%.