Biodegradation Of Phenanthrene And Heavy Metal Removal By Burkholderia Fungorum FM-2

Polycyclic aromatic hydrocarbons?PAHs?fused-ring aromatic compounds consisting of two or more fused benzene and/or pentacyclic rings.Phenanthrene?PHE?was selected as a model PAH because it is a widespread pollutant with typical PAH characteristics including a K region and a bent structure.PHE is also often present in acidic environments or heavy metal contaminated areas,which leads PHE biodegradation efficiency to decline.Biodegradation is considered an efficient,economic and facile physicochemical process for the treatment of environments contaminated with PAHs.In this work,PHE-degrading strains screened from oil-contaminated soils in an oil field in Xinjiang may possess sophisticated catabolic pathway and the ability to tolerate,extreme conditions,toxic metals and limited nutrients.Finally,biotechnology was used to realize the bioremediation for PHE and heavy metal co-contaminated environment,through simulating soil experiments subjected to multiple pollutions.The specific research work is as follows:?1?PHE-degrading strain was isolated from the oil-contaminated soil in Xinjiang Oilfield and named FM-2.After morphological observation,strain FM-2 exhibited Gram-negative,motile,short rod-like phenotypic characteristics.Colonies grown on LB agar were¹-2 mm in diameter,milky white in colour,circular,convex,and transparent with intact margins.Analysis of 16S rRNA gene sequence confirmed that strain FM-2 was Burkholderia sp.The impact of PHE concentration,cultivation duration,temperature,salinity,pH and rhamnolipid concentration on PHE degradation by strain FM-2 were studied by single factor optimization experiments.The optimal PHE degradation conditions:PHE concentration 300 mg·L^-1,culture time 2d,temperature 25°C,pH 7,rhamnolipid concentration 20 mg·L^-1.Under these conditions,the strain had a PHE(300 mg·L^-1)degradation rate of 100%after 2-day culture.?2?The impact of the addition of different rhamnolipid concentrations on cell surface hydrophobicity?CSH?,lipopolysaccharide?LPS?and Zeta potential were studied.The results showed that low concentration of rhamnolipid could decrease CSH of strain cell surface,promote the release of LPS of strain FM-2,and increase the negative charge on the cell surface,thus improving PHE degradation efficiency of strain FM-2.?3?HPLC-MS analysis showed that the intermediate products of strain FM-2 were1-hydroxy-2-naphthoic acid,1-naphthol,salicylic acid and catechol in the process of degrading PHE.Because phthalic acid was not detected,it was speculated that the process of PHE degradation by strain FM-2 was the salicylic acid pathway.?4?The impact of heavy metals to PHE degradation was studied.The results showed that low concentration of Zn???had a positive effect on PHE degradation,while low concentrations of Cd???and Pb???strongly inhibited the PHE-degrading capability of strain FM-2.ICP-OES,SEM-EDS and FTIR spectroscopy analyses to metal accumulation and adsorption further confirmed that metal ions were associated with the cell wall and intracellular space of strain FM-2.Similar results were obtained for simulating contaminated soil bioremediation experiments.Strain FM-2 displayed versatile catabolic activity and the ability to degrade PHE under the stress of high concentrations of toxic metals.FM-2 exhibited high tolerance to acidic pH?3-7?and very few PAH-degrading bacteria capable of oxidising PHE at acidic pH have been reported to date.The impact of heavy metals on the bioremediation of PHE in soil were investigated,and the findings suggest that FM-2 has potential for combined bioremediation of soils co-contaminated with PHE and heavy metals.These results suggest that the multifunctional B.fungorum FM-2 strain may offer a cost-effective bioremediation strategy for environments contaminated with multiple pollutants.