The Co‐Metabolic Bioremediation of <scp>Benzo[a]pyrene</scp> Contaminated Soil by <i>Achromobacter xylosoxidans</i> <scp>B‐2</scp> and Its Effect on Indigenous Microbial Community

Benzo[a]pyrene (BaP) is a persistent polycyclic aromatic hydrocarbon (PAH) that poses significant environmental and health risks. Co-metabolic bioremediation, which uses additional carbon sources to enhance microbial degradation, offers a promising approach for BaP removal. This study investigated the effects of different co-metabolic carbon sources on the growth of Achromobacter xylosoxidans B-2 and its efficiency in degrading BaP in both mineral salt medium (MSM) and BaP-contaminated soil. The addition of supplementary carbon sources, particularly starch and salicylic acid, significantly enhanced strain B-2 growth and BaP removal in MSM (p < 0.05), with the highest degradation rate reaching 46.35% in the starch-supplemented group. In soil, salicylic acid and starch also markedly improved BaP degradation, achieving 47.99% and 23.53% removal (both p < 0.01) after 30 days, respectively, compared to only 9.78% in the BaP-only group. Metagenomic analysis revealed that co-substrate amendments significantly altered soil microbiota, enriching PAH-degrading genera such as Achromobacter, especially the introduced A. xylosoxidans. This enrichment was accompanied by reduced overall microbial diversity, indicating strong selective pressure from the amendments. Functional gene profiling based on metagenomic data indicated an increased abundance of key PAH-degrading enzymes, including dioxygenases and dehydrogenases, in response to co-substrate addition. Redundancy analysis further indicated that environmental factors such as pH, organic matter, and phosphorus were significantly correlated with microbial community composition and BaP degradation efficiency. These findings demonstrate that co-metabolism not only enhances BaP removal but also drives functional and ecological changes in soil microbiota, providing mechanistic insight and practical guidance for improved bioremediation strategies.