Screening of crude oil-degrading bacteria from plant rhizosphere producing ACC deaminase and study on their degradation and growth promoting characteristics
The rhizosphere soil of Haloxylon ammodendron was collected from 3 areas of petroleum pollution and salinization around Karamay oilfield in Xinjiang,and physicochemical properties of soil were determined.Using crude oil and 1-amino-cyclopropane-1-carboxylic acid(ACC)as the only carbon and nitrogen source,respectively,two strains with strong saline-alkali tolerance,high ACC deaminase activity and strong crude oil degrading ability were isolated from soil samples.The specific activity of ACC deaminase in strains S8-1 and W8-4 was(0.17±0.06)and(0.77±0.08)U/mg,respectively.The specific activity of ACC deaminase in strain W8-4 was significantly higher than that in strain S8-1.Through the determination of emulsification property,it was found that the emulsification rates of strains W8-4 and S8-1 were(54.92±5.04)%and(49.59±3.69)%,respectively,indicating that they had solubilization and could reduce the interfacial tension of oil and water.The results of 7-day degradation test showed that the crude oil degradation rates of the two strains were 52.82%and 41.38%,respectively.After morphological observation,physiological and biochemical identification and 16S rDNA sequence analysis,S8-1 was identified as the strain of Pseudomonas gessardii and W8-4 was identified as the strain of Pseudommonas sp..By studying the influence of different environmental conditions on the degradation effects of crude oil of the strain,it was found that when the degradation time was 7 days and the rotating speed of the shaker was 180 r/min,the optimal degradation conditions of strain S8-1 were 4%inoculation amount,initial pH 7,30℃ culture temperature and 0.5 g/L crude oil concentration.The optimum degradation conditions of strain W8-4 were 5%inoculation amount,initial pH 8,30℃ culture temperature and 2.5 g/L crude oil concentration.At this time,the crude oil degradation rates of the two strains were 55.16%and 57.89%,respectively.The results of growth promoting ability showed that both strains had the ability of nitrogen fixation and phosphorus solubilization.Therefore,these two strains can provide valuable bacterial resources for the treatment of salinized petroleum polluted soil in the future.
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