Oil concentration and microbial communities jointly control marine oil spills biodegradation: Emergent threshold...

Biodegradation has been extensively investigated and implemented in the remediation of global marine oil spills, with the rate of degradation being a critical factor in the duration of cleanup efforts. While various groups have elucidated the key impacts of oil concentration, the role of microbial community structure has received limited attention. Here, we utilized integrated chemical and biological analysis (16S rRNA sequencing and metatranscriptomics) to systematically characterize the biodegradation patterns and associated mechanisms at three oil environmental concentrations (2 ppm, 20 ppm, and 200 ppm). The results showed the degradation rate was inversely proportional to the oil concentration (R² > 0.65). We further found and elucidated the effect of low-promotion-high-suppression effect on oil spill degradation rate. Meanwhile, we identified the threshold range of oil concentration (10¹ ∼ 10² ppm). Below the range, microbial communities dominated by the Proteobacteria phylum (relative abundance > 63 %) dominate degradation through enhanced gene expression and metabolic pathways. Conversely, microbial dominant roles are superseded by oil concentration. In conclusion, microbial community and oil concentration jointly influence oil spills biodegradation. Based on this, critical summaries predict the behavioral fate of oil spills on time scales ranging from months to years. These findings provide actionable insights for designing targeted bioremediation programs based on the range of oil spill concentrations.