A Biosurfactant Producing Strain MSP117 And Its Effect On Phenanthrene Degradation By CFP312

Polycyclic Aromatic Hydrocarbons(PAHs)are a type of widely distributed organic pollutants that are highly hydrophobic and difficult to degrade.Low water solubility is the main factor leading to the limited biodegradation of PAHs.Biosurfactants are environmentally friendly and easily degradable microbial secondary metabolites,which can significantly increase the apparent solubility of PAHs.In addition,in soils with high rare earth content,PAHs degrading bacterium was susceptible to the stress of rare earth ions and their metabolism is limited.However,there are few studies on the effect of rare earth ions on the metabolism of PAHs degrading bacteria.Based on this,biosurfactant producing bacteria were screened.Subsequently,the biosurfactant was preliminarily purified and its classification was identified,and its solubilization to phenanthrene was determined at the same time.Immediately afterwards,this article further tested the strain's ability to adsorb rare earth ions and determined some basic influencing factors.Finally,by adding inactivated cells and co-cultivation methods,the main mechanism of strains to alleviate the stress of rare earth ions on PAHs degrading bacteria was analyzed.The specific research content and results are as follows:1.Strain screening,identification and preservation.Samples were collected from oil-rich soil or water,and subjected to enrichment culture,single colony separation,primary oil drainage ring screening and emulsification performance re-screening to obtain a strain MSP117 that produces biosurfactants.The adsorption experiment results of rare earth Ce³⁺show that MSP117 has a good adsorption capacity for rare earth ions.Observed by the plate,the MSP117 colony appears white,dry,flat,and opaque.After48 h incubation on the plate,the diameter is about 0.6-0.8 mm.Microscopic examination revealed that the cells were rod-shaped,Gram-positive bacteria,and sporulated.In the physiological and biochemical tests,the strain can grow using glucose and sucrose,and the contact enzymes,oxidases and starch hydrolyzing enzymes are all positive.Combining colony characteristics,microscopic observation,physiological and biochemical and 16s r DNA homology analysis,the strain MSP117 was identified as Bacillus subtilis,its Genbank accession number was MW412499,and the deposit number was CICC 25064.3.Characteristics of the biosurfactant.The fermentation process of strain MSP117is relatively slow,but the glucose consumption is rapid.In the later period of fermentation,the culture solution gradually acidified and produced a large amount of biosurfactant.According to the results of the methylene blue experiment,the biosurfactant was determined to be non-ionic.Thin layer chromatography experiments show that it was a glycolipid biosurfactant.In addition,the biosurfactant has a significant solubilizing effect on phenanthrene.4.The adsorption of rare earth ions by MSP117 cells.The experiment found that after the cells of strain MSP117 were dried(drying or freeze-dried),the adsorption effect of rare earth ions decreased compared with that of wet cells;at p H=5,7,and 9,the adsorption capacity of strain MSP117 increased with alkalinity.However,the change of temperature has little effect on the adsorption capacity of strain MSP117.With the increase of the concentration of interfering ion NH⁴⁺,the adsorption of Ce³⁺by cells was not affected,but the adsorption amount of rare earth Y³⁺gradually decreased.5.The effect of MSP117 on the biodegradation of phenanthrene under rare earth stress.With the increase of the concentration of rare earth ions,the phenanthrene metabolism activity of the degrading bacteria CFP312 was stressed,but the glucose metabolism was not affected.When glucose and phenanthrene coexist,the strain can first use glucose and then phenanthrene to form secondary growth.In the presence of high concentrations of rare earth ions,the biodegradation of phenanthrene is still limited.Adding the strain MSP117 inactivated cells to the culture system,or under the conditions of co-cultivation of MSP117 and CFP312,the stress effect of rare earth elements on phenanthrene degradation is effectively alleviated.