Bioefficiency of Indigenous Microbial Rhodanese in Clean-up of CyanideContaminated Stream in Modakeke, Ile-Ife, Osun State, Nigeria

Abstract

Cyanide pollution of aquatic environment has become a great concern in Nigeria because of the increase in cassava cultivation. In Nigeria, cassava processing milling plants are usually situated around streams or rivers such that the waste from each stages of processing easily find their way into these water bodies as effluents and waste waters. Extracellular rhodanese of Klebsiella edwardsii isolated from Atutulala stream, Modakeke, where cassava is being processed, was assessed for its bioremediation potential. Cyanide concentration of the stream was analysed for six months. Four bacterial isolates were screened for their ability to degrade free cyanide and the best strain was further screened for rhodanese producing ability. The enzyme was purified by 85% ammonium sulphate precipitation and diethyl aminoethyl-cellulose ion-exchange chromatography. The pure enzyme had a specific activity of 0.0473 Rhodanese Unit mg-1 with a purification fold of 4.56 and a percentage yield of 30.30%. The enzyme demonstrated a broad pH range but the optimum pH was at 6.0 while the optimum temperature was 60°C. The bioremediation potential of the enzyme was assessed under various conditions such as the field pH and temperature as well as optimum pH and temperature using the cyanide contaminated water as substrate source in a typical assay protocol. The enzyme was able to convert 1.6481 μmol of cyanide to thiocyanate in the water sample at optimum pH and temperature of the enzyme. It could be concluded from the study that at optimum pH and temperature, rhodanese exhibited remediation activity in cyanide contaminated aquatic ecosystems and thus, can be used for its restoration.