Indigenous microorganisms residing in oil sands tailings biodegrade residual bitumen.

The purpose of this study was to determine the capacity of indigenous microbes in tailings to degrade bitumen aerobically, and if acetate biostimulation further improved degradation. Fluid fine tailings, from Base Mine Lake (BML), were used as microbial inocula, and bitumen in the tailings served as a potential carbon source during the experiment. The tailings were capped with 0.22 µm-filtered BML surface water with or without BML bitumen and acetate addition and incubated for 100 days at 20 °C. CO2 production and petroleum hydrocarbon reductions (50-70% for the biostimulation treatment) in the tailings were observed. DNA was extracted directly from the tailings, and increased bacterial density was observed by qPCR targeting the rpoB gene in the biostimulated group. 16 S rRNA sequencing was used to determine microbial composition profiles in each treatment group. The microbial communities indigenous to the tailings shifted after the bitumen was added. Acidovorax, Rhodoferax, Pseudomonas and Pseudoxanthomonas spp. significantly increased compared to the original microbial community and demonstrated tolerance to bitumen-based toxicity. The first three genera showed more potential for biostimulation treatment with acetate and may be important bitumen/hydrocarbon-degraders in an oil sands end pit lake environment.