Screening And Degradation Mechanism Of Polycyclic Aromatic Hydrocarbon Halophilic Bacteria

Polycyclic aromatic hydrocarbon(PAHs)compounds are ubiquitous in the environment and are internationally recognized as carcinogenic organic pollutants.Due to their refractory degradation,they have long half-life and are easily deposited in soils,lakes and rivers.Biodegradation is highly efficient,safe,economical,and convenient.In this study,strain DY123-6 capable of degrading phenanthrene was isolated and screened from soils conta minated with polycyclic aromatic hydrocarbons for a long time.By morphological,physiological and biochemical analysis,Biolog analysis,16S rRNA sequence analysis and genome-wide analysis of strain DY123-6,it was found that strain DY123-6 belongs to genus,but it is suspected of new species,so the strain DY123-6 is now named for Pseudomonas sp.DY123-6.The effects of different environmental conditions on the ability of strain DY123-6 to degrade phenanthrene were analyzed by single factor experiments.The results showed that strain DY 123-6 had a wide tolerance range for temperature,salt concentration and pH.The tolerance strain DY123-6 of temperature is 15-40?(optimum 30?),pH 5.0-11.0(optimal 8.0),NaCl concentration(v/w)is 0%-7%(optimal 3%),therefore strain DY123-6 is a moderately halophilic degrading strain.Through the study of the substrate concentration,it was found that the strain DY123-6 can not only be used in low concentration environment(min:0.5-10 mg/L),but also can be degraded at high concentration(20-400 mg/L).At a concentration of 20-80 mg/L,strain DY123-6 can be completely degraded.Therefore,the strain DY123-6 can degrade 98 mg/L of phenanthrene by 98%under the optimum degradation conditions for 6 days.The substrate spectrum analysis showed that the strain DY123-6 can efficiently degrade naphthalene,fluorene,acenaphthene and biphenyl.Studies have shown that when NAP and PHE are used together as carbon source and energy source,strain DY123-6 can completely degrade 100 mg/L of phenanthrene within 4 days.The intermediate product of the degradation of phenanthrene by strain DY123-6 was detected by HPLC.It was confirmed that strain DY123-6 completely degraded phenanthrene by ring-opening at the 3,4 position to produce 1-hydroxy-2-naphthoic acid and entering the naphthalene pathway.The whole genome sequencing of the strain DY123-6 was carried out by using Next-Generation Sequencing(NGS),and the whole genome sequence of the strain was obtained.The strain DY123-6 contains a circular genome(3.5Mb,G+C content 63.74%)without plasmid,and the coding sequence of the genome is predicted to have 3395 coding sequences(CDS),of which 3117,1929 and 2564 CDS were respectively Comment to COG,KEGG,GO.By comparative genomic analysis,dioxygenase gene encoding PAHs,including a complete degradation gene cluster of biphenyl,phenanthrene and naphthalene,was obtained.Differential proteomics analysis was performed using iTRAQ technology,and the difference proteomics analyzed by the difference in substrate(PHE-NAP co-degradation,PHE degradation)under the same conditions.It was found that the protein gene expression level of PHE-degraded gene cluster nahAbAcAdBCDHL was significantly up-regulated compared with PHE degradation in the case of PHE-NAP co-degradation,and the cell-permeability protein,ATP-binding protein and ferrite associated with degradation were degraded.The expression level of transport proteins was also significantly up-regulated.