The effect of heavy metals on thiocyanate biodegradation by an autotrophic microbial consortium enriched from mine taili
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ENVIRONMENTAL BIOTECHNOLOGY
The effect of heavy metals on thiocyanate biodegradation by an autotrophic microbial consortium enriched from mine tailings Farhad Shafiei 1
&
Mathew P. Watts 1
&
Lukas Pajank 1 & John W. Moreau 1,2
Received: 16 June 2020 / Revised: 17 October 2020 / Accepted: 26 October 2020 # The Author(s) 2020
Abstract Bioremediation systems represent an environmentally sustainable approach to degrading industrially generated thiocyanate (SCN−), with low energy demand and operational costs and high efficiency and substrate specificity. However, heavy metals present in mine tailings effluent may hamper process efficiency by poisoning thiocyanate-degrading microbial consortia. Here, we experimentally tested the tolerance of an autotrophic SCN−-degrading bacterial consortium enriched from gold mine tailings for Zn, Cu, Ni, Cr, and As. All of the selected metals inhibited SCN− biodegradation to different extents, depending on concentration. At pH of 7.8 and 30 °C, complete inhibition of SCN− biodegradation by Zn, Cu, Ni, and Cr occurred at 20, 5, 10, and 6 mg L−1, respectively. Lower concentrations of these metals decreased the rate of SCN− biodegradation, with relatively long lag times. Interestingly, the microbial consortium tolerated As even at 500 mg L−1, although both the rate and extent of SCN− biodegradation were affected. Potentially, the observed As tolerance could be explained by the origin of our microbial consortium in tailings derived from As-enriched gold ore (arsenopyrite). This study highlights the importance of considering metal co-contamination in bioreactor design and operation for SCN− bioremediation at mine sites. Key points • Both the efficiency and rate of SCN− biodegradation were inhibited by heavy metals, to different degrees depending on type and concentration of metal. • The autotrophic microbial consortium was capable of tolerating high concentrations of As, potential having adapted to higher As levels derived from the tailings source. Keywords Metal toxicity . Metal tolerance . Bioremediation . Geomicrobiology . Gold mining
Introduction For higher organisms, thiocyanate (SCN−) is a known goitrogen, i.e., a chemical with deleterious anti-thyroid effects with prolonged exposure (Ermans and Bourdoux 1989); acute SCN− poisoning can also occur (Gould et al. 2012). The toxicity of this compound occurs at blood serum concentrations greater than 1 mg per 100 mL (Lage et al. 1994). Both chronic
* John W. Moreau [email protected] 1
School of Earth Sciences, The University of Melbourne, Parkville, VIC 3010, Australia
2
Present address: School of Geographical & Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
and acute toxicity of SCN− to aquatic organisms, including Daphnia magna (Parkhurst et al. 1979) and various fish species (Bhunia et al. 2000; Kevan and Dixon 1991; Lanno and Dixon 1996), has also been demonstrated. Gold processing commonly involves mixing finely ground ores with the lixiviant sodium cyanide (Woffenden et al. 2008). Gold-bearing ores also n
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