Successional dynamics of microbial communities and remediation of petroleum-contaminated soils during pilot-scale bioaugmentation.

Petroleum-contaminated soils pose serious global ecological and health risks. This pilot-scale study (120 days, 25 m2) aimed to evaluate the field efficacy of a compound microbial agent, ECT (composed of Ralstonia sp. CP, Rhizobium sp. BX, and Acinetobacter sp. FL), for bioaugmented remediation of heavily petroleum-polluted soil (initial TPH: 45,178 mg kg-1). ECT achieved an excellent TPH removal rate of 91.61%, with exogenous strains successfully colonizing the soil and maintaining high relative abundances (Ralstonia 42.1%, Rhizobium 10.0%, Acinetobacter 12.3% at day 120). High-throughput sequencing revealed a dynamic community succession, where introduced strains were associated with indigenous genera (Sphingomonas, Thermomonas, Microbacterium, and Pseudoxanthomonas), suggesting the formation of a degradation network. Post-remediation, soil quality improved significantly, with increases in total nitrogen (11%), total phosphorus (28%), available potassium (35%), and enzyme activities (dehydrogenase and polyphenol oxidase). Although the α-diversity declined temporarily, by the 120th day, ecosystem stability showed signs of recovery through reoccupation of the niche by native bacteria. Notably, colonized exogenous strains stabilized in abundance rather than proliferating indefinitely, suggesting ecosystem self-regulation under the conditions tested. Temperature was the most influential environmental factor governing community succession. These findings demonstrate the field potential of ECT at the pilot scale and provide community-level insights into microbial succession during bioaugmentation, offering a reference for pilot-scale bioremediation of petroleum-contaminated soils.