Studies On Biological Properties Of Alcanivorax Sp Xb And Pseudomonas Sp X1 And Remediation Of Oil-contaminated Soil

Environmental pollution caused by petroleum extraction and use has becoming more and more obvious.Bioremediation is an environmentally friendly,non-secondary pollution and low-cost remediation technology,which has broad application prospects in the remediation of contaminated soils.The selection of high-efficiency petroleum-degrading bacteria is one of the key aspects of microbial-based bioremediation technologies.In this paper the biological properties and petroleum degradation characteristics of two efficient petroleum degrading strains of Alcanivorax sp.Xb and Pseudomonas sp.X1 were compared.And the degradation efficiencies of the three strains on various alkanes and aromatics were investigated.The bioremediation effect of the strains on oil-contaminated desert soil and agricultural yellow soil was studied by different strain combinations.The kinetics of the petroleum degradation in remediation of the contaminated soils by these bacterial strains were also investigated.The main results were as follows:Alcanivorax sp.Xb grew normally at 25～40℃,with the optimum growth temperature of 35℃.The strain grew normally in the range of p H 5～8,with the optimum growth p H 8.The strain grew in the range of Na Cl concentration of 2%～7.5%,with the optimum growth salinity of 5%.Pseudomonas sp.X1 grew normally at25～35℃,the optimal growth temperature was 30℃,it could grow normally during the p H 5～8,with the optimal growth p H 8.The strain grew best under the condition of Na Cl concentration of 1.5%.After 7 days of growth of the two petroleum degrading bacteria strains in the base medium containing crude oil,the petroleum degradation rates were 50.67%and 49.93%,respectively.The degradation studies of the mixed alkanes and aromatics of different molecular amounts showed that Alcanivorax sp.Xb and Pseudomonas sp.X1 grew in basic media at concentrations of mixed alkanes and mixed aromatics.After 7 days of degradation,Alcanivorax sp.Xb degraded 100%of decane,dodecane,tetradecan and pentadecan.The degradation rate of the remaining components exceeded 92.90%.In the mixed aromatics,the degradation rate of Alcanivorax sp.Xb was above 99.50%for each component.The degradation rates of Pseudomonas sp.X1 for the components of alkanes were above 88.13%,among which the degradation rates of decane,tetradecan,hexadecane,docosane and tetracosane reached 100%,and the degradation rates of the components of mixed aromatic hydrocarbons exceeded 96.80%.The metabolic kinetics and bacterial growth curves of Alcanivorax sp.Xb in the polycyclic aromatic hydrocarbons pyrene media were investigated.The strains were found to grow well in the basic medium containing 100 mg/L pyrene.When the initial inoculum was 7.3×10⁵ CFU/m L,the bacterial cells grew exponentially from 0 to 2 days,and the cell number reached a peak at 4 days.The bacterial concentration reached1.81×10⁷ CFU/m L and decreased to the lowest after 10 days with a bacterial concentration of 1.1×10⁶ CFU/m L.GC-MS analysis showed that the degradation of pyrene by Alcanivorax sp.Xb was 36.88%at 5 days and 51.57%at 10 days.The typical desert soil and farmland loess were contaminated with the oil.The initial TPHs concentrations of the two kinds of soils were 20.171 g/kg and 19.632 g/kg.Alcanivorax sp.Xb,Pseudomonas sp.X1 and R.erythropolis KB1 were used with single strain or multiple strain combinations to restore the oil contaminated loess.Different combinations of strains were found to have different effects on the remediation of the contaminated loess through 30-day bioremediation.The petroleum degradation ability of R.erythropolis KB1 was significant in the monoculture group,with 80.82%degradation rate.In the two-strain combined remediation group,the R.erythropolis KB1-Pseudomonas sp.X1 group and the R.erythropolis KB1-Alcanivorax sp.Xb group had stronger remediation ability,with the oil degradation rates of 89.28%and 83.91%respectively after 30 days.In the combined restoration group of the three strains,the degradation rate of the R.erythropolis KB1-Alcanivorax sp.Xb-Pseudomonas sp.X1 group was 76.01%.The reaction rate constant k and oil degradation half-life t_1/2 of R.erythropolis KB1 monoculture group were 0.021 and4.549 days.In the two strains combined groups the group of R.erythropolis KB1 and Pseudomonas sp.X1 had the largest reaction rate constant and had the shortest petroleum degradation half-life,with the reaction constant k and petroleum degradation half-life t_1/2 of 0.074 and 3.291 days respectively.The reaction constants k and oil degradation half-lives t_1/2 of the three-strain combined remediation group of R.erythropolis KB1-Alcanivorax sp.Xb-Pseudomonas sp.X1 were 0.047 and 3.743days,respectively.The bioremediation of the petroleum-contaminated desert soil was studied during50 days by using different strain combinations.The degradation rate of the control experimental group was 77.19%.The best degradation was achieved in the monoculture remediation group of R.erythropolis KB1 with a degrading rate of92.04%.The degrading rate of the two-strain group of R.erythropolis KB1-Pseudomonas sp.X1 was 80.34%.The degradation rate was 86.21%in the three-strain remediation group of R.erythropolis KB1-Alcanivorax sp.Xb-Pseudomonas sp.X1（-）.A degrading rate of 94.28%in the three-strain remediation group adding soil relaxant of R.erythropolis KB1-Alcanivorax sp.Xb-Pseudomonas sp.X1（+）was obtainded.The addition of a soil relaxant effectively improved the degradation of petroleum contaminants.GC-MS analysis of the changes of petroleum hydrocarbon species in the desert soil showed that the degradation rates of pristane,phytane,diesel fraction and residual oil fraction were above 98.49%in the group of R.erythropolis KB1.The degradation rates of Alcanivorax sp.Xb reached 92.99%for all fractions and 100%for pristane.The degradation rate of Pseudomonas sp.X1 was above 93.51%for each component.The degradation of the petroleum fraction by R.erythropolis KB1-Pseudomonas sp.X1 group was more than 89.90%.The degradation rates of the four fractions by R.erythropolis KB1-Alcanivorax sp.Xb-Pseudomonas sp.X1（+）with soil loosener remediation group were more than 99.54%.