Virtual Posters

Bioremediation is challenging to apply in High Arctic soils due to technical and financial constraints. In addition, soil temperatures only rise above 0°C for ~2 months each year, limiting the amount of time that hydrocarbon degraders can actively degrade contaminants. A common and cost-efficient in situ treatment is the addition of nitrogen-based fertilizer to soil, as nitrogen is often the limiting nutrient in terrestrial Arctic environments. Nitrogen addition is thought to stimulate the growth and activity of the microbial community, but little is known about how it is specifically used and divided between organisms. Bacteria vary widely in their ability to metabolize petroleum hydrocarbons, so the question becomes: which hydrocarbon-degrading bacteria are most effectively using added nitrogen? To answer this, we used a novel DNA-SIP approach, adding 14N- and 15N-labeled monoammonium phosphate to petroleum-contaminated soils in Alert, Nunavut, Canada. Fractions from CsCl gradients in each sample were amplified with primers specific to the 16S rRNA and alkane monooxygenase B genes, while 454-pyrosequencing and qPCR were used to determine the identity and quantity of taxonomic groups in each fraction. The DNA-SIP experiment showed that many hydrocarbon-degrading bacterial groups were 15N enriched. The degree to which these bacteria incorporated the isotope varied greatly, with Sphingomonadaceae, a family that is known to be involved in aromatic hydrocarbon degradation, showing the highest degree of incorporation, and therefore growth. This result demonstrates that blanket applications of nutrients do not equally stimulate the entire bacterial community. It is still unknown whether the bacteria that most readily benefit from nutrient amendments are the same bacteria that most efficiently degrade petroleum contaminants in the Arctic. A better understanding of how various groups of hydrocarbon-degraders contribute to the breakdown of petroleum contaminants will facilitate the design of more targeted bioremediation treatments in the future.