Metagenomic Analysis of the Bioremediation of Diesel-Contaminated Canadian High Arctic Soils

Soil bacteria, no matter where you might find them, exhibit incredible adaptations, some of which allow for living in the most extreme climates and subsisting on a wide-array of compounds that seem utterly foreign to us in terms of providing nourishment. Cold-adapted bacteria that live in the soil of the Canadian High Arctic are a great example of this. This area is one of particular interest because recent increases in logging and a large-scale oil spill that took place in 2004 have deposited excess hydrocarbons into the soil, disrupting the delicate balance of this vulnerable ecosystem. Yergeau et al. (2012) had two objectives in this study: to identify the expressed genes that code for cold-adapted enzymes that allow these organisms to live in such an extreme climate and to measure the degradation rates of hydrocarbons in the Arctic soil. Genes that are adapted to the cold could be transposed into crops that would benefit from cold resistance, which is a reason these bacterial species are getting so much attention, in addition to their ability to clean up environmental pollutants. The authors of this study identified about four species that are actively involved in biodegradation of diesel hydrocarbons. Using PCR techniques, they pinpointed some the genes involved in this process, while also recording the relative abundance of the four key species at different time intervals. In all tested soil samples, these four species were found in lower densities before soil contamination when less hydrocarbons were present, and increased dramatically when resampled a month later, indicating that these species indeed rely on the hydrocarbons to live.—Edward McLean

Yergeau E, Sanschagrin S, Beaumier D, Greer CW. 2012 Metagenomic Analysis of the Bioremediation of Diesel-Contaminated Canadian High Arctic Soils. PLoS ONE 7(1) 2012.

Bioremediation in the Arctic continues to be an issue of growing concern. Logging in Canada and the Russian Boreal Forest has steadily increased over the last few decades, and the heavy machinery used to get this job done as efficiently as possible contaminate the soil with diesel pollutants, which decreases the soil pH and puts environmental stress on the whole community. In 2004, a spill occurred in Alert, Canada, and this study was conducted as a result: contaminated soil was put into biopiles and monoammonium phosphate was added as fertilizer to stimulate aerobic microorganisms. Yergeau et al. collected samples from these biopiles (and control samples from nearby uncontaminated soil) and their results were strong. One question they had was whether in situ or ex situ bioremediation was more effective. They found that transporting the soil for off-site remediation got the job done faster: the hydrocarbon concentration fell below safe limits much more quickly when they were able to manipulate the soil in the lab. However, removing the soil in this way can be disastrous to the community and upset the biological balance of the area, so they concluded that whenever possible in situ remediation is the preferred path.

The experiment occurred at three time intervals: directly after collection and analysis, one month into the experiment, and one year after the initial collection period. All soil samples that showed signs of excessive hydrocarbons also contained a higher concentration of those bacterial species that digest them when compared to the control soil samples. Their abundance was greatest one month after the contamination; one year later, most of the diesel byproducts had been consumed, so their abundance dropped back down to normal levels. Digesting environmental pollutants at temperatures below 4C is an incredible ability that bears continued study. As we begin to understand what combination of genes allow for cold-resistant enzymes, we will have a better chance of efficiently and harmlessly cleansing contaminated soils from around the world. Bioremediation is still in its youth and there is a lot of testing that needs to be done. But in terms of cheap, safe, and effective methods to remove pollutants from soil or the water, one would be hard-pressed to find a better way than using preexisting biological machinery and natural processes.

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