Ecological Effect Of Rhodococcus Erythropolis Kb1 On Alfalfa Degradation Of Petroleum Hydrocarbons

With the rapid development of the industrialization of society,the demand for oil in all aspects of human life has become greater and greater.Therefore,the environmental pollution caused by petroleum,its derivatives and petroleum products is becoming increasingly serious.When petroleum pollutants enter the soil,they will damage the soil's self-healing ability,and the petroleum pollutants stay in the soil for a long time,which not only affects soil microorganisms and plants,but also endangers human health.Bioremediation has the advantages of low cost,environmental friendliness,and no secondary pollution.It has become the preferred ecological remediation technology in the field of environmental protection.Among them,the combined plant-microbe remediation technology has the best effect and has received much attention in recent years.It is of great theoretical and practical significance to use plants combined with highly effective oil-degrading bacteria to perform plant-microbe repair of petroleum-contaminated soil.This article intends to simulate petroleum-contaminated soil under laboratory conditions.A total of 4 petroleum concentration gradients are set up,which are 0 mg/kg,2500mg/kg,5000 mg/kg,and 7500 mg/kg.Alfalfa is used as the test plant.A strain KB1 was used to simulate the repair of petroleum-contaminated soil.Samples were collected at 45 days,60 days,and 75 days,and physiological and biochemical indicators,physical and chemical properties of soil,soil enzyme activity,petroleum hydrocarbon degradation rate,and stress resistance indicators of the test plants were measured.The contents of NO,H₂O₂,JA,and SA signal molecules in the plant are used to analyze the response of soil environmental factors to the plant-microbe joint repair of petroleum-contaminated soil,and provide a scientific theoretical basis for the repair of petroleum-contaminated soil.The main results are as follows:?1?Through partial physiological and biochemical tests on Rhodococcus erythropolis KB1 and alfalfa seed germination test under laboratory conditions,the study found that the methyl red test reaction of Rhodococcus erythroides KB1 was negative,nitrate reduction,V-P test Both catalase reactions were positive.Except that lactose could not be used,glucose,fructose,and maltose could all be grown as the sole carbon source.Qualitative test results showed that Rhodococcus rhodococcus KB1 did not have nitrogenase and cellulase production.Output capacity,indoleacetic acid?IAA?,ACC deaminase and iron carrier have a certain amount of output,the output of indoleacetic acid?IAA?is 16.41±0.132(mg·L^-1),ACC deaminase The output was 4.894±0.201(?mol?-butanone acid·mg^-1pro·h^-1).The results of alfalfa seed germination test showed that with the increase of petroleum concentration,the germination rate,germination potential,germination index,and vitality index of alfalfa seeds decreased;after soaking with strain KB1,the germination rate of alfalfa seeds could be increased.The group increased,and it can be seen that Rhodococcus rhodococcus KB1 has a certain role in promoting growth.?2?Strain condition optimization results showed that the optimal growth conditions of Rhodococcus rubidus KB1 were 35?,pH 7.0,and NaCl mass concentration of 2.0%.The strain degradation kinetics results showed that the fitted Monod equation was reasonable.The obtained maximum specific degradation rate vmax=12.37 mg/?L·d?,and the half-rate constant Ks=79.43 mg/L.The results show that KB1 and alfalfa joint remediation can significantly promote the remediation effect of oil-contaminated soil,and the addition of KB1 can promote alfalfa plant growth,improve alfalfa stress resistance and antioxidant enzyme activity.?3?Determination of stress resistance indicators and signal molecules of collected alfalfa plants.The results showed that as for the control group,as the crude oil concentration in the soil increased,the contents of malonaldehyde,proline,superoxide dismutase,and peroxidase increased,indicating that the alfalfa plant's stress resistance decreased;?Soaking seeds with KB1?,with the increase of crude oil concentration in the soil,although the various indicators are still on the rise,compared with the control group,the contents of each indicator have been reduced,which shows that the strain KB1 helps to improve Stress resistance of alfalfa plants.?4?Analysis of the physical and chemical properties,nutrient content,and enzyme activity of the soil collected at different times can be obtained.The soil of each treatment group is neutral,and the organic matter content is between 1.5%and2.5%.With the increase,the total nitrogen and total phosphorus contents in the soil nutrient content increased,the available nitrogen and available phosphorus contents decreased,and the total potassium and available potassium contents remained basically unchanged.After soaking in KB1,the available nitrogen and available phosphorus in the soil were significantly increased.And fast-acting potassium content,indicating that the strain can increase the plant's utilization of nitrogen,phosphorus,and potassium in the soil to promote its own growth and development.