Isolation of asphaltene-tolerant microbial strains from North Saskatchewan river sediment and evaluation of their interaction mechanisms with asphaltenes.

Oil spills in freshwater pose environmental, social, and economic challenges. The mobility of spilled oil in flowing water and its strong association with sediments leave behind hydrocarbons that can persist in the sediment long after a spill. While recent research has focused on the immediate effects of diluted bitumen spills, less is known about the impact of heavy fractions of bitumen, particularly asphaltenes (Asp) on sediments, and the key microbial taxa involved in their degradation. This study aimed to evaluate how deposited Asp, as the external carbon source, influences sediment microbial community dynamics, isolate and identify asphaltene-tolerant microbial taxa, and investigate the interactions between these taxa and Asp. Sediments from the North Saskatchewan River were incubated with Asp for over 100 days. Analysis of the water overlaying Asp-sorbed sediment revealed hydrocarbon leaching and elevated concentrations of sulfate and nitrogen species in Asp-exposed treatments, suggesting solubilization of Asp components into the water. Culture-based methods and 16S rRNA gene sequencing revealed a shift from a Pseudomonas-dominated microbial community in unexposed sediment to Asp-tolerant species, such as Roseateles aquatilis, Sphingopyxis chilensis, and Methylobacterium thiocyanatum. R. aquatilis survived and proliferated with Asp as the external carbon source over the exposure period and exhibited strong adhesion to Asp, driven by its high cell surface hydrophobicity, whereas the other strains show no direct interaction with Asp. The findings highlight the potential role of R. aquatilis in natural bioremediation processes of asphaltene-contaminated freshwater sediments.