Effects of temperature and moisture on the co-inoculation remediation of petroleum-polluted soil by bacteria and nematodes

Petroleum contamination poses a serious global environment threat. Microorganisms have substantial potential for petroleum degradation and are environmentally friendly, but their effectiveness varies with environmental conditions. Nematodes can further enhance oil removal efficiency, but the mechanisms underlying their combined remediation with bacteria, particularly in response to environmental changes, remain unclear. To address this knowledge gap, this study investigated the effects of temperature and moisture on oil remediation by introducing nematodes into contaminated soil under three levels of temperature and moisture. Petroleum-contaminated soil at 22 °C and 50 % humidity served as the baseline treatment (SPN), with the following variations: lower temperature (14 °C, SPN_LT), higher temperature (30 °C, SPN_HT), lower moisture (40 %, SPN_LM), and higher moisture (60 %, SPN_HM). After 168 days, results indicated that nematodes consistently facilitated petroleum degradation across all tested conditions by modifying bacterial community structure and the relationships among bacterial genera. Notably, petroleum content was significantly lower in the SPN_HM and SPN_HT treatments, indicating that both elevated temperature and increased moisture enhance oil removal efficiency. Interestingly, the Shannon index increased significantly with rising moisture but decreased with increasing temperature. Principal coordinates analysis (PCoA) further indicated that temperature had a stronger influence on bacterial community structure than moisture. These findings suggest that temperature and moisture enhance oil remediation through distinct mechanisms. Furthermore, correlation and co-occurrence network analyses revealed that different petroleum-degrading bacterial genera formed separate network modules. These modules included both degradative and associated functional genera, with significant positive correlations, indicating that hydrocarbon breakdown is driven by diverse bacterial consortia composed of both degraders and supportive functional bacteria. In conclusion, our study demonstrates that increased moisture and temperature, combined with nematode addition, significantly improve petroleum degradation efficiency. This improvement is attributed to the interactions between nematodes and bacteria, highlighting the importance of both petroleum-degrading genera and their functional partners. Future research should focus on the roles of auxiliary functional bacteria and nematodes in promoting microbial biodegradation.