Research On Molecular Mechanism Of Polycylic Aromatic Hydrocarbons Degradation By Halophiles

As the close relationship between petroleum industry and saline environments,more and more PAHs are found to be accumulated in saline and hypersaline environments.Therefore,biodegradation of PAHs in saline and hypersaline environments has got much attention.In this study,halophilic PAHs degrading consortium CY-1 was enriched from petroleum polluted soil in Shengli oil field using phenanthrene as the sole carbon source under 10% salinity.Consortium CY-1 was mainly composed of Marinobacter(40.67%),Marispirillum(18.15%)and Halomonas(9.15%),which was able to degrade phenanthrene under a wide range of salinities(from 3% to 20%).By the combination of detected metabolic intermediates and constracted catabolic gene clone libraries,phenanthrene metabolic pathway in consortium CY-1 was investigated,which was composed of a single upstream pathway and several downstream pathways.The upstream pathway was initiated by dioxygenation at the C1 and C2 positions,and the produced phenanthrene-dihydroglycol was further transformed to 1H2 N.Martelella and Marinobacter was responsible for this process,and with the increase in salinity,Marinobacter was found to be more important than Martelella.C23 O pathway was an important downstream pathway in consortium and mainly contribute in the prophase of phenanthrene degrading process.C12 O is the dominant downstream pathway in the anaphase of phenanthrene degradation.G12 O and P34 O pathway was predicted to be less important.Microbes in consortium CY-1 contributed to phenanthrene degrading process via different downstream pathways.Marinobacter,which was a dominant genera in consortium CY-1,was widely detected in petroleum contaminated marine environments and was considered to be a worldwide genus for PAHs elimination in marine environments.However,the PAHdegrading mechanism in Marinobacter was still not been investigated.In this study,both upstream and downstream PAH-degrading clusters in Marinobacter was firstly cloned.Combined with the intermediates detection and the genetic information,lacking of nahGlike gene was predicted to be the reason of Marinobacter incapable to mineralize phenanthrene and the accumulaition of intermediate 1H2 N in the degrading process.This was also predicted to be the reason for the low PAH-degrading efficiency of lot's of isolated Marinobacter species.Supplying nahG-like genes and utilizing the intermediates produced in the PAH-degradation was predicted to be the syntrophic interaction mode of Marinobacter and Halomonas or other microbes.Upstream PAH-degrading gene cluster cloned from Marinobacter(hpah1 cluster)was predicted to be evolutionary related with classic nah-like PAH-degrading clusters and formed a novel clade in the phylogenic tree illustrated based on the amino acid sequence of all nah-like PAH-degrading clusters.The horizontal transfer process and evolutionary implication of nah-like PAH-degrading cluster was further investigated and the nag gene cluter was proposed to be the progenitor of the whole known nah-like gene clusters.Moreover,according to the characteristics of the amino acid sequence,the appropriate evolution mechanism in the process of horizontal transfer to the marine environment of nah-like PAH-degrading gene clusters was deduced.