Background and Aim:
Persian Gulf (PG) is estimated to host ca. ۴۵% of the world’s oil reserves. As a consequence of natural seepage and anthropogenic contaminations, this habitat has been continuously exposed to oil derivatives contamination. To explore the impact of oil contamination on the PG microbial community, we investigate the composition, dynamics, and metabolic potential of the microbial community of water and surface sediment samples along the contamination continuum in the PG.Methods: Three different locations of the PG were selected for sampling based on their different level of expected oil contamination. Sampling was carried out in spring and summer ۲۰۱۸ from water column and surface sediment in the vicinity of Hormuz, Asaluyeh and Khark. Metagenomes were sequenced from the extracted environmental DNA. Community composition was inferred from ۱۶S rRNA gene sequences recovered from unassembled reads also metagenome assembled genomes (MAGs) were reconstructed, annotated and their taxonomic affiliation was assigned.Results: Amongst six sequenced samples from PG, a sediment sample from Khark Island represent heavy contamination with oil derivatives. Hormoz water and sediment samples showed the microbial community similar to other marine ecosystems. Whereas, oil contamination of the Asalouyeh and Khark water samples was below the detection limit. The continuous exposure to trace amounts of oil derivatives contamination has evidently shifted the expected marine microbial profile toward the dominance of Oceanospirillales, Flavobacteriales, Alteromonadales, and Rhodobacterales orders. Exposure to oil contamination supposedly triggers selective enrichment pressure on the local microbial community favouring those capable of degradation. Exploring the metabolic profile of reconstructed MAGs shows that Khark sediment sample contains MAGs with oil-degrading ability affiliated to Immundisolibacter, Roseovarius, Lutimaribacter, and Halomonas genera. The presence of enzymes involved in the degradation of various hydrocarbons e.g. xylene, toluene, carbazole, catechol, phenylacetate and cymene was also confirmed in the genomic content of the reconstructed MAGs.Conclusion: long-standing trace oil contamination can impose a consistent selection pressure on the microbial community. This continuous exposure to trace oil derivatives contamination similar to oil spill events changes the microbial community composition. In both cases the community composition converges towards higher dominance of oil-degrading constituents.