Cyanide Biodegradation and its Research Highlights

Cyanide is a highly toxic compound found in wastewater from industries like mining and jewellery. These wastewaters often contain other harmful pollutants such as arsenic and heavy metals, which can combine with cyanide to form even more dangerous compounds. To develop effective ways to clean up these pollutants, it’s important to understand how microorganisms can tolerate and break them down. However, most studies look at these pollutants individually rather than together.

In the MIBIREM project, cyanide is a key pollutant targeted by bioremediation technologies. Cyanide-polluted sites where soil sampling is being performed in the MIBIREM project can be viewed on the site map, these include Rinteln and Stokah in Germany and Simmering as well as Siebenhirten in Vienna. Below, we report on the most recent studies on cyanides published in 2024.

(C)Shutterstock: Gold mining

Research Highlights

The study by Welman-Purchase et al. (2024) addresses the significant concern of cyanide-containing mining waste disposal in gold extraction tailings, particularly in South Africa. While previous research has shown that microorganisms can degrade cyanide, this study is the first to explore the natural attenuation capabilities of indigenous microorganisms in contaminated tailings.

Moreover, researchers used geochemical and metagenomics techniques to uncover how indigenous bacteria like Alicyclobacillus, Sulfobacillus, Acinetobacter, and Achromobacter can degrade cyanide using enzymes such as nitrilase, nitrile hydratase (Nhase), and thiocyanate. The lack of nitrogen sources appears to induce the use of cyanide, aiding its natural breakdown. The study identified bacteria that could serve as the first line of defense in detoxifying cyanide in mining tailings. These bacteria possess the genomic tools to break down cyanide, which could be valuable for future bioremediation efforts. Cyanide pollution poses significant environmental risks, but biological techniques for cyanide degradation offer ecological and economic benefits, producing fewer harmful by-products compared to conventional chemical methods. However, these methods face challenges, such as effectiveness being influenced by environmental factors like temperature, pH, and nutrient availability.

(C)Shutterstock: Bioremediation

Rangel-González et al. (2024) compile information on various biological species, including plants, bacteria, and fungi, studied from 2012 to 2022 for their ability to degrade cyanide. They highlight the effectiveness of biological methods as viable alternatives to physical and chemical approaches and emphasize the need for further research on plant species and the use of living organisms at contaminated sites under uncontrolled conditions.

Key bacteria for cyanide degradation

Key bacteria identified for their ability to degrade cyanide include:

– Pseudomonas pseudoalcaligenes: Degrades cyanide and produces by-products like ammonia and carbon dioxide.

– Bacillus pumilus: Produces enzymes that break down cyanide into less harmful compounds.

– Klebsiella pneumoniae: Utilizes cyanide as a nitrogen source, effective in bioremediation processes.

– Rhodococcus sp.: Known for degrading a wide range of toxic compounds, including cyanide.

The review also discusses the potential of using plants for cyanide degradation, known as phytoremediation. Certain species of willow trees and plants like cassava, which naturally produce cyanogenic glycosides, have enzymes that can detoxify cyanide. These plants can absorb and break down cyanide through their natural metabolic processes, offering an environmentally friendly and cost-effective solution to cyanide pollution.

(c)Shutterstock: Cyanide liquid

Overall, Rangel-González et al. (2024) emphasize the importance of continuing research to develop more effective and sustainable methods for cyanide biodegradation. By understanding and utilizing the natural abilities of microorganisms and plants, we can work towards a cleaner and safer environment.

Furthermore, the review by Olaya‐Abril et al. (2024) highlights how bacteria can reduce the harmful effects of cyanide, arsenic, and heavy metals, and how these pollutants interact. It emphasizes the use of advanced biological techniques for cleaning up industrial wastes and the importance of monitoring enzymes that break down cyanide. Future research should focus on studying microbial communities in diverse environments, such as acid mine drainage sites, to develop effective bioremediation strategies.

The study by Abdullahi Taiwo et al. (2024) evaluated the use of indigenous cyanide-degrading bacterial strains to treat cassava mill effluent (CME) in Nigeria. The researchers identified bacteria such as Pseudomonas putida, Bacillus subtilis, Alcaligenes faecalis, and Leuconostoc mesenteroides. Their bioremediation approach significantly reduced cyanide levels and other pollutants, showing promise for improving public health.

(C)Shutterstock: Cyanide danger sign

Conclusion

In conclusion, the research highlights the significant progress made in understanding and utilizing biological methods for cyanide biodegradation. Studies have shown that indigenous microorganisms and plants possess the potential to effectively degrade cyanide and other harmful pollutants in contaminated environments. Further research and development are needed to optimize these processes and address associated challenges.

References

Abdullahi Taiwo, J.H., Oluwabukola Kudirat, A., Wakili, T. and Jimoh, F.A., 2024. Evaluation of the Potential of Immobilized Cyanide-Degrading Bacteria for the Bioremediation of Cassava Mill Effluent. Jordan Journal of Biological Sciences, 17(3).

Olaya‐Abril, A., Biełło, K., Rodríguez‐Caballero, G., Cabello, P., Sáez, L.P., Moreno‐Vivián, C., Luque‐Almagro, V.M. and Roldán, M.D., 2024. Bacterial tolerance and detoxification of cyanide, arsenic and heavy metals: Holistic approaches applied to bioremediation of industrial complex wastes. Microbial Biotechnology, 17(1), p.e14399.

Rangel-González, M.G., Solís-Domínguez, F.A., Herrera-Martínez, A., Carrillo-Gonzalez, R., Lopez-Luna, J., Del Carmen Angeles González-Chávez, M. and Rodríguez, M.D., 2024. Cyanide biodegradation: a scoping review. International Journal of Environmental Science and Technology, pp.1-26.

Welman-Purchase, M.D., Castillo, J., Gomez-Arias, A., Matu, A. and Hansen, R.N., 2024. First insight into the natural biodegradation of cyanide in a gold tailings environment enriched in cyanide compounds. Science of the Total Environment, 906, p.167174.

Author: Tiziana Centofanti

Environmental Consultant, RTDS Group