Cyanide bioremediation potential of Klebsiella oxytoca JCM 1665 rhodanese immobilized on alginate-glutaraldehyde beads

Abstract

Rhodanese, a cyanide detoxifying enzyme synthesized by Klebsiella oxytoca was immobilized on alginate-glutaraldehyde beads. K. oxytoca was isolated from industrial wastewater and identified using 16S rRNA gene sequencing with gene bank accession number MN590525. Rhodanese was produced from the bacterium through submerged fermentation. The rhodanese produced was immobilized on alginate-glutaraldehyde beads; its physicochemical properties and cyanide bioremediation potential were compared with the free enzyme. In this study, the optimum concentrations of glutaraldehyde and sodium alginate that resulted in the highest enzyme immobilization yield (89.71%) and lower leakage (1.45 ± 0.2%) were 4.5% (v/v) and 2.5 (%) respectively. The optimum temperature for free and immobilized rhodanese was observed at 50 °C and 60 °C respectively while the optimum pH for both preparations was 6.0. The free rhodanese retained 31% and 23% of relative activity at 60 °C and 70 °C respectively after 30 minutes of incubation while immobilized rhodanese retained about 95% and 70% at the same condition. The entrapped rhodanese showed activity until the 10th cycle and maintained about 70% of its activity after the fifth cycle. After 180 minutes of incubation, the free and immobilized rhodanese was able to biodegrade 115 mg/L cyanide to 77 mg/L and 45 mg/L respectively with degradation efficiency of 33 and 64.34%. These results suggest that immobilized K. oxytoca rhodanese may be profitably exploited in bioremediation of cyanide polluted environment due to its thermal stability and its reusability.