Synergistic Potential of Contamination Remediation and Carbon Fixation: Functional Resilience of Carbon Fixation in Petroleum Hydrocarbon-Degrading Microbial Communities Under Enhanced Natural Attenuation

Enhanced Natural Attenuation (ENA) can accelerate pollutant degradation by adding electron acceptors or nutrients. However, its impact on carbon-fixing microorganisms, which are widely found in the natural attenuation process, remains unclear. In this study, four types of ENA materials were added in batch experiments. Chemical analysis and metagenomic sequencing were employed to analyze the degradation kinetics of petroleum hydrocarbons, the consumption pattern of nitrate, as well as the functional genes and population evolution characteristics of carbon-fixing microorganisms. Results showed that nitrate-based enhancement materials significantly improved the petroleum hydrocarbon degradation rate but suppressed the expression of some carbon fixation genes, such as those involved in the Calvin-Benson-Bassham cycle. Nevertheless, the overall abundance of carbon fixation genes did not show a notable decline. Dominant bacterial genera such as <i>Pseudomonas</i> and <i>Achromobacter</i> possessed both hydrocarbon degradation and carbon fixation capabilities. Although the calcium peroxide treatment group only achieved a 40% petroleum hydrocarbon degradation rate, it significantly promoted the abundance of carbon fixation genes involved in the reductive tricarboxylic acid cycle pathway. Therefore, ENA alters carbon fixation pathways but does not diminish carbon fixation potential, indicating its potential for synergistically achieving pollution remediation and carbon fixation.