1. Introduction
With the growth of the global population and the massive utilization of petroleum products, petrochemical production continues to develop, resulting in marine and land environmental pollution. This can happen during oil production, transportation, use and leakage (Ramadass et al., 2018; Baoune et al., 2019). Due to the complex composition, high biological toxicity, and low bioavailability of petroleum hydrocarbons, they are harmful to soil, groundwater, and the regional ecological environment (Dariush et al., 2007, Hassan and AI-Jawhari 2014). Moreover, the oil site soil is often accompanied by salinization, which makes its remediation extremely difficult.
The soil microbiota plays a vital role in the material cycles and energy flow in the soil system, such as the biogeochemical cycle of nitrogen, carbon and phosphorus (Liu et al., 2020). Furthermore, when soil is disturbed by pollutants, soil microorganisms react immediately to resist the invasion of pollutants. Many studies have used DNA-based technology to study the microbiota in petroleum hydrocarbons or organic pollutants polluted soil, water, and sediments (Sheng et al., 2016, Zhou et al., 2020, Hamdan and Salam 2020). As an oil-polluted lake in France, the profiles of the sedimentary bacterial community have been associated with the oil-contaminated gradient (Paisse et al., 2018). The complex pollution composition exerts selective pressure on these bacterial communities, and the oil degrading bacteria do not increase with the increase of oil pollutants. On the contrary, the study on the microbial community of an oil contaminated site in China found that there were more oil-degrading microorganisms in polluted soils than in clean soils (Liu et al., 2019). However, few studies concentrated on the effects of oil contamination on soil microbial community in the long or short term, and few studies focused on culture-dependent microorganisms.
Microorganisms do not exist alone in the soil, but form a complex matrix of ecological interaction. With the exception of the environmental factors, community interactions also affect microbial behavior, including the interaction between prokaryotes and eukaryotes. The coexistence of bacteria and fungi in the same environment inevitably leads to material and energy exchange among them (De Boer et al., 2005; Benoit et al., 2015; Warmink et al., 2009). Further studies have been carried out in natural samples describing the coexistence between bacterial and fungal communities recently. The network study for limited-length polymorphism endpoint data showed that bacterial and fungal communities and soil properties were linked, as shown by a typical correlation module (De Menezes et al., 2015). The network study provides richer insights into microbial assemblages compared to simple indices of heterogeneity and structure. In addition, they supplement an important facet to our knowledge of the interactions among microbiota or between a known community and environmental parameters such as soil contamination. Up to now, though, few networks was assembled for soil microbial communities under petroleum contamination, especially under differing pollution duration.
Metals and metalloids are indispensable for agricultural products and land. In a previous study, Haraguchi (2004) described for the first time the “metallomic” as an “integrated biometal science,” trying to supply a systematic perception of the absorption, change, function, and excretion of the metal within biological systems. Metallomics concentrates on a systematic investigation of metallomes and the interactions and functional associations of metals or metalloid species with gene, protein, metabolite, and other biomolecule in cells (Ge and Sun 2009). The examination of metals obtained from soil—the metallomes—can be detected through inductively coupled plasma–mass spectrometry (ICP–MS). Meanwhile, a previous work has shown that the shift of the soil ionome resulting from different fertilization can drive the assembly of the soil microbiome and alter microbial interaction and function (Liu et al., 2020). However, to date, little is known about how the soil metallome reacts to oil contamination in the long- or short-term.
To explore the short-term and long-term impacts of petroleum pollution on soil, the physicochemical properties, the contents of 18 metals, the diversity, composition, and structure of soil microbial communities were determined. In addition, three strains of bacteria with high petroleum degradation efficiency were isolated from long-term petroleum-contaminated soil, and the degradation efficiency of their synthetic community on petroleum hydrocarbons and the growth of maize seedlings under oil pollution stress were explored. We hypothesized that: 1) Petroleum pollution in different years caused significant differences in the diversity and composition of soil microbial community. 2) Petroleum pollution with different years will significantly change the topological parameters of the soil microbial network.