Application of H412R mutant alkaline phosphatase for removal of heavy metals from single-ion solutions and effluents

Enzyme-mediated bioremediation is an eco-friendly process for removing hazardous toxic heavy metals from the environment. The potential use of mutant alkaline phosphatase H412R for bioprecipitation of heavy metals such as Co2+, Cd2+, Cr6+, Ni2+, Mn2+ and Zn2+ from single-ion solutions and electroplating effluents was analysed in the present study. Purified wild-type and H412R mutant alkaline phosphatase enzymes were incubated with an initial concentration of 100 ppm metal solutions for various time periods along with the substrate p-nitrophenol phosphate. Upon catalysis, the enzyme–substrate reaction liberates inorganic phosphate which in turn binds to heavy metals and precipitates them as metal-phosphates. The amount of metal ions precipitated as a result of formation of metal ion-phosphate complexes was determined by estimating the amount of free metal ions present in the solution using atomic absorption spectroscopy. Based on the results obtained, maximum bioprecipitation of metal ions, in general, was observed at 180 min of incubation period. The H412R mutant enzyme exhibited higher efficiency and precipitated 96% of Mn2+ from electroplating effluent and 92% of Co2+ from the metal ion solution. The pattern of precipitation of various metal ions was in the order Co2+ > Cr6+ > Ni2+ > Cd2+ > Mn2+ > Zn2+ for H412R mutant enzyme and Co2+ > Cr6+ > Zn2+ > Ni2+ > Cd2+ > Mn2+ for wild-type enzyme. The results emphasise the use of novel H412R, a mutated alkaline phosphatase enzyme in its catalytic site, as an efficient way of achieving bioremediation of heavy metals from real-time effluents.