Abstract

VARGAS-SERNA, Claudia L.; CARMONA-OROZCO, María L.  and  PANAY, Aram J.. Biodegradation of cyanide via recombinant cyanide dehydratase from Bacillus pumilus expressed heterologously in Escherichia coli. Rev. colomb. biotecnol [online]. 2020, vol.22, n.1, pp.27-35. ISSN 0123-3475.  https://doi.org/10.15446/rev.colomb.biote.v22n1.79559.

Despite its high toxicity, cyanide is used in several industrial processes, and as a result, large volumes of cyanide wastewater need to be treated prior to discharge. Enzymatic degradation of industrial cyanide wastewater by cyanide dihydratase, which is capable of converting cyanide to ammonia and formate, is an attractive alternative to conventional chemical methods of cyanide decontamination. However, the main impediment to the use of this enzyme for the biodegradation of cyanide is its intolerance to the alkaline pH at which cyanide waste is kept and its low thermoresistance. In the present study, the catalytic properties of whole Escherichia coli cells overexpressing a cyanide dihydratase gene from Bacillus pumilus were compared to those of the purified enzyme under conditions similar to those found in industrial cyanide wastewater. In addition, the capacity of whole cells to degrade free cyanide in contaminated wastewater resulting from the gold mining process was also determined. The characteristics of intracellular enzyme, relative to purified enzyme, included increased thermostability (>60% activity at 50°C), as well as greater tolerance to heavy metals, and to a lesser extent pH (20% activity remaining at pH 9.0) On the other hand, enzymatic degradation of 70% of free cyanide (initial concentration 528 mM) in the industrial sample was achieved only after dilution. Nevertheless, the increased thermostability observed for intracellular CynD suggest that whole cells of E. coli overexpressing CynD are suited for process that operate at elevated temperatures (50°C), a limitation observed for the purified enzyme.

Keywords : Biodegradation; cyanide; cyanide dihydratase; gold mining effluents; whole cells.

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