Larissa Smith to Present Poster on Molecular Genetic Tools for Monitoring Selenium Reduction at Tailings and Mine Waste 2023

Larissa Smith will present the poster “Molecular Genetic Tools for Monitoring Selenium Reduction and Metabolic Functions in Microbial Communities” at the Tailings and Mine Waste 2023 conference. SiREM’s Jeff Roberts will also attend the conference, which runs from November 5 to 8 at the JW Marriott Parq Hotel in Vancouver, British Columbia.

Larissa Smith is a Scientist in the Treatability division of SiREM. Larissa’s coauthors on the paper are SiREM’s Asma Rahman, Melody Vachon, Phil Dennis, and Jeff Roberts and Geosyntec’s Silvia Mancini, Andrew Holmes, and Rachel James.

The Tailings and Mine Waste Conference presents state-of-art and state-of-practice information regarding mill tailings and mine waste. It also addresses current and future topics facing the tailings, mining, and environmental communities.


Microbial communities can play a significant role in the treatment of metals at mine sites, often through direct microbial metabolic reduction. Soluble metal ions can act as the electron acceptor in microbial respiration with concurrent decreases in their solubility and toxicity, for example the reduction of aqueous selenate to precipitated elemental selenium. The use of molecular genetic tools including targeted quantitative polymerase chain reaction (qPCR) allows quantitative monitoring of specific genes involved in metal reduction processes, such as selenate reductases. Additionally, genetic colony identification and next generation sequencing of 16S rRNA gene amplicons (NGS) can be used provide comprehensive microbial profiles that are used to monitor important microbial groups with metabolic functions, such as sulfate reduction, nitrate reduction, or groups that directly precipitate metals. In this study qPCR tests, NGS, and differential plating methods combined with genetic colony identification were used to detect and characterize microbial communities for metals reduction and detoxification processes at a selenium site.

Selenate metabolic pathways were used to develop qPCR tests specific to selenate reductase genes, including srdA and serA, which were used to quantify specialized selenium reducing microbial communities in samples of geologic material from a mine site. Other qPCR tests targeting sulfate reducing bacteria and nitrate reducing bacteria were used to quantify non-specialized selenium degraders. For the purposes of monitoring selenium metabolism through NGS, an open-source microbial functional database was modified to include a new functional category made up of 27 microbial taxa documented to be involved in selenium reduction. The database was then used to summarize the proportion of selenium metabolizers in the context of other metabolic functions. This provided rapid and easily interpretable outputs of complex data. The data indicated the presence of both specialized and non-specialized selenium reducers in the samples tested. In another approach, microbes from geologic material from a known selenium reducing site were plated and colonies of selenite reducing bacteria were grown and isolated. PCR amplification of the 16S rRNA gene combined with Sanger sequencing were used to identify the species of bacteria that reduced selenium based on the formation of characteristic red colonies on the selenite-amended agar plates. This is an example of using classical plate-based microbiology methods combined with molecular biology that provides a method for quickly isolating and identifying selenite reducing microbes that may be yet to be identified in the literature.

The combination of molecular biological tools used in this study provided multiple lenses to view selenium metabolizing communities and can vastly increase our ability to understand how microbiology impacts metals treatment processes for selenium and other toxic metals.

More Information

About the event: Tailings and Mine Waste 2023

For consultation regarding metals treatment, contact Larissa Smith at

For consultation regarding molecular genetic testing, contact Phil Dennis at

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