| Polycyclic aromatic hydrocarbons(PAHs)are typical persistent organic pollutants in soil.The PAHs pollution in soil is getting increasingly worse in China,which seriously endangers the safety of agricultural products and the health of soil ecosystems.Microbial remediation technology pocesses an array of merits such as economic,green and environmental friendly,and has become one of the main remediation methods for PAHs contaminated soil.However,due to the influence of soil components and environmental factors,the efficiency of microbial remediation is relatively low and needs to be further improved.With high-molecular-weight PAH-degrading bacteria,Paracoccus aminovorans HPD-2,as the research object,this research systematically studied the effects of graphene on the growth of the strain HPD-2.Fourier infrared spectroscopy,Raman spectroscopy,and metabolomics were applied to reveal the interaction mechanism between graphene and HPD-2,and the effect of the complex microbial inoculant of graphene and HPD-2 on the degradation of PAHs in soil was further explored by soil culture experiments.The research results are helpful for understanding and scientifically evaluatiing the effects of graphene on environmental microorganisms,and provide new ideas for microbial remediation of PAHscontaminated soil.The main results obtained in this study are as follows:(1)The results for the experiments on the effects of functionalized graphene(graphene oxide(GO)and sulfonated graphene(SG))on the growth of HPD-2 showed that the effect of graphene on the growth of HPD-2 is not only related to the type and concentration of graphene,but also the nutritional level of the culture system.Low concentrations of graphene(0-10 mg / L)had no effect on the growth of HPD-2,and higher concentration of graphene(100 mg / L)could significantly promote the growth of HPD-2(p <0.05).Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)electron microscopy results showed that both types of graphene can promote the secretion of extracellular polymer(EPS)of HPD-2,and the promotion effect of GO is more obvious.(2)The results from raman spectroscopy,infrared spectroscopy,and intracellular metabolomics showed that,the disorder of GO structure at low concentrations increased after interaction with HPD-2,and more obvious interactions took place between HPD-2 and higher concentrations of graphene,which presented a certain degree of stacking on bacterial surface.Cell surface proteins,amino acids and extracellular polysaccharides are all involved in the interaction.Compared with GO,SG has a weaker interaction with the bacterial surface.When GO was added at 20 mg/L,the sulfur metabolism pathway was the largest influenced metabolic pathways,which promoted the growth rate of HPD-2.When GO was added at 100 mg/L,the growth and metabolism of HPD-2 was promoted through the TCA cycle metabolic pathway.(3)The complex microbial inoculant significantly promoted the microbial degradation efficiency of PAHs in soil(p <0.05).After 35 days of cultivation,the total degradation rate of 12 PAHs in original soil was as high as 70.31%.The complex microbial inoculant significantly increased the quantity of bacterial communities in soil,and increased the amount of functional genes including the dioxygenase genes nid A,PAH-RHD? GN and PAH-RHD? GP genes,which are related to the degradation of PAHs in soil.The high-throughput sequencing results demonstrated that the slowrelease effect of mmobilized bacteria.Soil available potassium content and soil cation exchange capacity(CEC)were both increased,indicating that the addition of microbial inoculants could improve soil nutrients and soil properties. |
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