SynCom improves carbon fixation capacity in phenanthrene-contaminated soils by reshaping microbial communities

Soil microorganisms play a crucial role in CO₂ fixation. However, it has been shown that organic pollution affects soil microbial ecological functions. In this study, phenanthrene (PHE) was found to significantly reduce soil carbon synthesis. To mitigate this effect, we constructed a synthetic community (SynCom) consisting of PHE-degrading bacterium Sphingobium sp. RS2 and carbon-sequestering archaeon Nitrososphaera viennensis EN76, and evaluated their effects. The results of the pot experiment indicated that 90.02% of the PHE was effectively removed from the soil and 81.07% of the PHE transferred to the lettuce was reduced by the addition of SynCom. Soil organic carbon, microbial carbon, and total carbon content were also significantly increased. Combining random forest model and partial least-squares path modeling (PLS-PM), we demonstrated that these effects were primarily driven by a continuous increase in the absolute abundance of soil carbon-fixing microorganisms and PHE-degrading microorganisms after SynCom addition. In addition, SynCom increased bacterial and archaeal α-diversity within the soil. Network analysis revealed that SynCom increased the modularity, robustness, and enhanced cooperation among bacterial communities, i.e., increased bacterial resistance to PHE. Importantly, SynCom altered some species identities and increased the number of keystone taxa significantly associated with carbon synthesis. Our constructed SynCom is expected to provide new strategies to address the dual pressures of soil organic pollution and climate change.