Enhanced cyanide biodegradation by immobilized crude extract of Rhodococcus UKMP-5M.

The crude extract of Rhodococcus UKMP-5M demonstrated excellent cyanide-degrading ability as reported previously. In the present study, the capability of the crude extract of the locally isolated bacterium was further enhanced by adopting the technology of immobilization. Among the matrices screened to encapsulate the crude extract, gellan gum emerged as the most suitable immobilization material exhibiting cyanide-degrading activity of 0.475(a) ± 0.003 mM/min/mg protein which exceeded the activity of cyanide-degrading enzyme by 61% and 361% in comparison to alginate carrier and non-immobilized crude extract, respectively. Additional measures taken to optimize the performance of the immobilization matrix in terms of concentration of gellan gum, concentration of calcium chloride, number of beads and bead size resulted in improved bead mechanical strength which supported higher biocatalyst activity by 63%. Interestingly, the immobilized crude extract demonstrated higher tolerance towards broad range of pH (5-10) and temperature (30°C-40°C), superior cyanide-degrading activity over time (lower Km-, lower Vmax than cell-free extract) and improved storage stability by maintaining 76% of its initial activity after 30 days at 4°C. Furthermore, repeated use of the gellan gum beads up to 20 batches without substantial loss in the catalytic activity was documented in the present study indicating that the durability of the beads and the stability of the enzyme are both above adequate. Collectively, the findings reported here revealed that the utilization of the encapsulated crude extract of Rhodococcus UKMP-5M can be considered as a novel attempt to develop an environmentally favourable and financially viable method in cyanide biodegradation.