Microbial community dynamics during biodegradation of crude oil and its response to biostimulation in Svalbard seawater at low temperature

The development of oil exploration activities and an increase in shipping in Arctic areas have elevated the risk of oil spills in this cold marine environment. The objective of this experimental study was to assess the effect of biostimulation on the microbial community abundance, structure, dynamics and metabolic potential for oil hydrocarbon degradation in oil-contaminated Arctic seawater. The combination of amplicon-based and shotgun sequencing together with genome-resolved metagenomics and omics data integration was applied for assessment of microbial community structure and metabolic properties in naphthenic crude oil-amended microcosms. Implementing biostimulation of seawater microbial community by addition of nutrients resulted in substantially elevated prokaryotic community abundance (103-fold), distinctly different bacterial community structure from initial seawater, 1.3-fold elevated normalized abundance of hydrocarbon degradation genes as well as enhanced biodegradation of crude oil by 12%. The analysis based on the integration of several microbial community structure estimates proved to be less prone to variations in individual taxa proportions estimates provided by different sequencing and taxonomic assignment methods, and produced consensus estimate of microbial community dynamics as well as effect of biostimulation on particular microbial taxa. The bacterial communities of biostimulated microcosms after four months of incubation were dominated by Gammaproteobacterial genera Pseudomonas, Marinomonas and Oleispira, succeeded by Cycloclasticus and Paraperlucidibaca after eight months of incubation. The majority of compiled 195 good quality metagenome assembled genomes (MAGs) showcased versatile hydrocarbon degradation gene profiles. The results revealed that biostimulation with nutrients promotes naphthenic oil degradation in Arctic seawater, but this strategy alone might not be enough to achieve bioremediation goals efficiently and within a reasonable timeframe.