Dynamic characteristics of genes involved in degradation of polycyclic aromatic hydrocarbons during natural attenuation of crude oil-contaminated soils in Xinjiang, China

Abstract:

There are few studies about the functional genes involved in the microbial degradation of polycyclic aromatic hydrocarbons (PAHs) in crude oil-contaminated soils in Xinjiang, and the correlations between environmental factors and functional genes remain unclear. [Objective] To reveal the structures and dynamic characteristics of key PAH-degrading genes during the natural attenuation of crude oil-contaminated sandy soils in Xinjiang. [Methods] We studied the variations in the physicochemical properties and the content of PAHs in the soils contaminated by crude oil for different years in the same oil production area in Zhundong Oilfield in Xinjiang. Amplicon sequencing was employed to study the dynamic characteristics of genes involved in the degradation of PAHs during the natural attenuation of crude oil-contaminated soils. Mental test was performed to explore the environmental driving factors. [Results] The soils contaminated by crude oil for 1 and 3 years had several physicochemical properties significantly different from the background soils, while that contaminated for 5 years had only 2 physicochemical properties significantly different, which gradually returned to normal levels with the natural attenuation of crude oil. Among the 16 PAHs studied, the remaining 14 PAHs except acenaphthylene and chrysene in the soils contaminated by crude oil for 1 year had higher content than those in the soil contaminated by crude oil for 3 and 5 years. The total PAHs and crude oil content in the 1-year contaminated soils were significantly higher than those in the 3-year and 5-year contaminated soils, which indicated that PAHs could be rapidly degraded in a short time after contamination. The amplicon sequencing results showed that the operational taxonomic units (OTUs) of naphthalene dioxygenase gene gradually increased with the extension of pollution years. The OTUs of aromatic ring-hydroxylating dioxygenase gene were annotated by BLAST alignment into 6 types of PAH-degrading genes, which first increased and then decreased with the extension of contamination time. The OTUs of aromatic ring-hydroxylating dioxygenase gene presented dramatically decreased diversity within 5 years of contamination. The Mental test results showed that the functional gene structures were significantly affected by soil soluble organic carbon and water content and not by PAHs. [Conclusion] The structures of PAH-degrading genes are mainly affected by soil soluble organic carbon and water content during the natural attenuation of crude oil-contaminated sandy soil in the Zhundong Oilfield of Xinjiang.