Co-metabolism of thiocyanate and free cyanide by Exiguobacterium acetylicum and Bacillus marisflavi under alkaline conditions

Lukhanyo Mekuto; Oluwadara Oluwaseun Alegbeleye; Seteno Karabo Obed Ntwampe; Maxwell Mewa Ngongang; John Baptist Mudumbi; Enoch A Akinpelu

doi:10.1007/s13205-016-0491-x

Co-metabolism of thiocyanate and free cyanide by Exiguobacterium acetylicum and Bacillus marisflavi under alkaline conditions

3 Biotech. 2016 Dec;6(2):173. doi: 10.1007/s13205-016-0491-x. Epub 2016 Aug 18.

Authors

Lukhanyo Mekuto¹, Oluwadara Oluwaseun Alegbeleye², Seteno Karabo Obed Ntwampe², Maxwell Mewa Ngongang^{2

3}, John Baptist Mudumbi², Enoch A Akinpelu²

Affiliations

¹ Bioresource Engineering Research Group, Department of Biotechnology, Cape Peninsula University of Technology, PO Box 652, Cape Town, 8000, South Africa. Lukhayo.Mekuto@gmail.com.
² Bioresource Engineering Research Group, Department of Biotechnology, Cape Peninsula University of Technology, PO Box 652, Cape Town, 8000, South Africa.
³ Department of Microbiology, Agricultural Research Council, Private Bag X5026, Stellenbosch, 7599, South Africa.

Abstract

The continuous discharge of cyanide-containing effluents to the environment has necessitated for the development of environmentally benign treatment processes that would result in complete detoxification of the cyanide-containing wastewaters, without producing additional environmental toxicants. Since biological detoxification of hazardous chemical compounds has been renowned for its robustness and environmental-friendliness, the ability of the Exiguobacterium acetylicum (GenBank accession number KT282229) and Bacillus marisflavi (GenBank accession number KR016603) to co-metabolise thiocyanate (SCN^-) and free cyanide (CN^-) under alkaline conditions was evaluated. E. acetylicum had an SCN^- degradation efficiency of 99.9 % from an initial SCN^- concentration of 150 mg SCN^-/L, but the organism was unable to degrade CN^-. Consequently, B. marisflavi had a CN^- degradation efficiency of 99 % from an initial concentration of 200 mg CN^-/L. Similarly, the organism was unable to degrade SCN^-; hence, this resulted in the evaluation of co-metabolism of SCN^- and CN^- by the two microbial species. Optimisation of operational conditions was evaluated using response surface methodology (RSM). A numeric optimisation technique was used to evaluate the optimisation of the input variables i.e. pH, temperature, SCN^- and CN^- concentrations. The optimum conditions were found to be as follows: pH 9.0, temperature 34 °C, 140 mg SCN^-/L and 205 mg CN^-/L under which complete SCN^- and CN^- degradation would be achieved over a 168-h period. Using the optimised data, co-metabolism of SCN^- and CN^- by both E. acetylicum and B. marisflavi was evaluated, achieving a combined degradation efficiency of ≥99.9 %. The high degradative capacity of these organisms has resulted in their supplementation on an active continuous biological degradation system that is treating both SCN^- and CN^-.

Keywords: B. marisflavi; Biodegradation; Co-metabolism; E. acetylicum; Free cyanide; Thiocyanate.