Breaking the priority effects facilitates the assembly and colonization of microbiomes toward enhanced petroleum hydrocarbon biodegradation

Priority effects exerted by indigenous microbial communities pose a major ecological barrier to bioremediation, preventing the stable establishment of introduced bioaugmentation strains through niche preemption and modification. Here, we developed a fine-tuned chemical pretreatment strategy to rapidly break the priority effects of indigenous microbiomes, thereby facilitating the targeted assembly and sustainable colonization of functional degraders in total petroleum hydrocarbon (TPH)-contaminated soil. Our results demonstrate that this strategy successfully overcame the priority effects of the indigenous microbiome, increasing the colonization capacity of the introduced degrader, Bacillus velezensis , by 560.43% and achieving a stable TPH removal efficiency of 63.21% without rebound. The intervention expanded the niche breadth of B. velezensis by 54.71% through niche modification, thereby reducing niche occupancy by indigenous microbiomes. Disruption of priority effects further reshaped microbial community assembly, promoting the enrichment of rare indigenous taxa with hydrocarbon-degrading potential, including Providencia and Citrobacter . Metagenomic and metabolic pathway analyses revealed that successful colonization of B. velezensis enhanced metabolic cooperation with indigenous rare degraders, collectively improving the degradation of both alkanes and polycyclic aromatic hydrocarbons. These findings establish a general ecological framework for manipulating microbiome assembly through priority-effect regulation and provide a practical strategy for microbiome engineering across contaminated ecosystems.