Studies On The Bioremediation Of Oil-contaminated Soil And Bacterial Diversity

Environmental pollution is becoming more and more serious with the development of the oil transportation and usage.Oil pollution not only affects the structure,nutrient and physicochemical properties of soil.The contaminants,which get through the soil into the biological chain,constitute a threat to the whole ecosystem and human health.It can be regarded as an effective method to degrade hydrocarbons,which are converted into carbon dioxide and water by microbes.In this paper,the degradation effect of several oil degrading bacteria on crude oil was studied.By adding oil degrading bacteria with different combination into the artificially contaminated soil,the oil degradation effect of the contaminated soil under natural conditions or adding oil degrading bacteria were compared.the changes of soil bacteria diversity during oil pollution and bioremediation process were researched with the high-throughput sequencing.The main results are as follows:4 highly efficient petroleum degrading bacteria were chosed,which were Rhodococcus erythropolis KB1,Pseudomonas aeruginosa 1217,Acinetobacter baumannii YM122 and Acinetobacter carbophilus JC3-1.The crude oil degradation rate of them,which were cultured 7 days with different conditions combination,was analyzed.The degradation rates of KB1,1217,YM122 were 49.21%,20.73%,19.75%,and 22.87%.And the degradation rates of KB1 and 1217,KB1 and YM122,KB1 and JC3-1,JC3-1 and 1217,1217 and YM122 were 49.21%,32.90%,31.01%,35.18% and32.68% respectively.Among them,the mixed group of KB1 and 1217 has the highest degradation rate.A certain amount of crude oil was added to the non polluting sienna,the natural degradation ability of crude oil was studied,the results showed that the artificially oil-contaminated soil could degrade the oil by adding water to tillage.After 40 days,the oil content of polluted soil decreased from 2929.22 mg·kg-1 to 2077.50 mg·kg-1,and the oil degradation rate was 29.08%.After 70 days' bioremediation,the soil oil content under natural degradation was 912.12 mg·kg-1,with the degradation rate of56.10%.Added the Pseudomonas aeruginosa 1217 agents and Rhodococcus erythropolis KB1 agents and mixed agents respectively into oil contaminated soil,we found that the oil contents of added 1217 agents,KB1 agents and mixed agents were reduced to 421.65 mg·kg-1,339.28 mg·kg-1,248.04 mg·kg-1,the degradation rates were 79.70%,83.67% and 88.06%,respectively.Compared with the naturaldegradation group,the degradation rates were increased by 23.60%,27.57% and32.96%,it showed that it has much better effect on soil remediation of different agents with single strain and mixed agents than with natural degradation,the bioremediation effect of the mixture group is better than the single group.The changes of main components in oil-contaminated soil were measured by GC-MS during the process of bioremediation.After seventy days degradation,the remained alkanes were undecane,3,7-dimethyl and tetradecane,2,6,10-trimethyl in the Pseudomonas aeruginosa 1217 group and Rhodococcus erythropolis KB1 group respectively,no alkanes were detected in the mixture group.While several long chain alkanes components were detected in the control group,including phytane and octadecane,3-ethyl-5-(2-ethyl butyl),etc.The diversity of bacterial communities in oil-contaminated soil and oil-degrading bacteria was studied by high-throughput sequencing technique.The results showed that before oil pollution,the number of the soil bacteria was abundant,including 34 phyla,70 classes,90 families,192 orders,and 675 genera,and the main dominant bacteria were Proteobacteria,Actinobacteria,Acidobacteria,Gemmatimonadetes,Planctomycetes,Firmicutes,Chloroflexi,Verrucomicrobia.The dominant bacteria were GP6,Gemmatimonas,Sphingomonas,Arthrobacter,GP4,Aridibacter,Skermanella,Povalibacter with the oil pollutants added and time extention,the level of bacteria in the soil has an evident change,the number of phyla reduced to 29.After 40 days of oil pollution,the abundance of actinobacteria became to the largest level,the abundance of Acidobacteria,Bacteriodetes,Gemmatimonadetes and Planctomycetes decreased significantly.After 110 days of oil pollution,the largetst abundance of bacteria was Proteobacteria,the abundance of Candidatus Saccharibacteria became gradually large,others nearly have no change.The composition level of genera has changed dramatically.The number of genera reduced from 654 to 500.The dominant bacteria were Sphingomonas,Pseudomonas,GP6,Iamia,GP16,Exiguobacterium,Aeromicrobium and Nocardioides.The diversity of soil groups was decreased including the bacteria of 29 phyla,507 genera,the level of dominant bacteria and the composition of the genera were changed greatly.The dominant bacteria were Pseudomonas,GP6,Gemmatimonas,GP4,Exiguobacterium,Stenotrophomonas,Nocardioides.The addition of different oil-degrading bacteria to enhancing bioremediation group has 31,32,29 phyla,and471,474,473 genera.The dominant bacteria of Pseudomonas aeruginosa 1217 group were Sphingomonas,Alglcola,Pseudomonas,Iamia,GP6,Nocardioides,Perlucidibaca,Exiguobacterium.The dominant bacteria of the mixed bacteria group of 1217 and KB1 were Sphingomonas,Iamia,Pseudomonas,GP6,GP4,Gemmatimonas,Aridibacter,Aquihabitans.The dominant bacteria of Rhodococcus erythropolis KB1 group were Sphingomonas,Iamia,Pseudomonas,GP6,Nocardioides,Aridibacter,Exiguobacterium,GP4,Gemmatimonas,Perlucidibaca,and Aeromicrobium.