Oil sands tailings ponds harbour a small core prokaryotic microbiome and diverse accessory communities.

Oil sands tailings ponds store the waste slurry generated by extracting bitumen from surface-mined oil (tar) sands ores. The ponds support diverse microbial communities involved in element cycling, greenhouse gas production, and hydrocarbon biodegradation that influence pond management and their environmental footprint. Since previous reports indicate that there are similar microbial metabolic functions amongst ponds, analogous microbiomes may be expected but ponds actually harbour distinct communities. Partial 16S rRNA gene pyrotag sequences from 95 samples were obtained from six ponds managed by three operators. From these we discerned a core prokaryotic microbiome, a subset of microbes shared amongst different samples, defined as operational taxonomic units (OTUs) at the lowest taxonomic level identifiable in individual ponds and pooled pond datatsets. Of the ∼1500-2700 OTUs detected per pond, 4-10 OTUs were shared among ≥75% of the samples per pond, but these few OTUs represented 39-54% of the ponds' sequence reads. Only 2-5 OTUs were shared by the majority of samples from all ponds. Thus the prokaryotic communities within these ponds consist of a few core taxa and numerous accessory members that likely afford resiliency and functional redundancy including roles in iron-, nitrogen- and sulfur-cycling, syntrophy, fermentation, and methanogenesis.