Study On The Degradation Of Hydrocarbon Compounds By Microbes Isolated From Nearshore Zone

As the largest ecosystem on earth,marine covers more than 90% of the biomass of the biosphere and contains abundant hydrocarbons resources.Compared with the high sea,the nearshore closer to the land are readily affected by human activities,and the types and contents of hydrocarbons are then relatively higher.Therefore,nearshore zone has become the most active hydrosphere of material cycle,energy flow and microbial activity in the whole ocean,and is also one of the key areas for us to study the biogeochemical cycle of the ocean.So far,the research on the screening and degradation mechanism of strains driving the degradation of petroleum hydrocarbons in the carbon cycle of nearshore zone has been reported in the literatures.However,there are few reports on isolation,screening and functional studies of strains capable of degradating aromatic hydrocarbons and aromatic polymers(such as lignin)in the nearshore zone,especially in the South and East China Seas.In this current study,firstly,12 hydrocarbon compounds,such as hexadecane,n-dodecylbenzene,alkali lignin,benzoic acid,p-coumaric acid and cinnamic acid,were used as the sole carbon source to isolate and screen bacterial strains with hydrocarbon degradation function from the South and East China Seas using the artificial seawater medium.A total of 63 bacterial strains having a degradation function of hydrocarbon compound were isolated.These strains belong to 10 genera,mainly Rhodococcus,Acinetobacter,Vibrio,Halomonas,Pseudomonas.Secondly,the growth characteristics and degradation functions of bacterial consortia NyZ-B and NyZ-S and bacterial strain Rhodococcus sp.NyZ306 were studied.The results showed that during the strain growth and lignin degradation,the degradation effect of bacterial consortium NyZ-B was always better than that of bacterial consortium NyZ-S.The results of growth characteristics indicated that the optimal temperature of bacterial consortium NyZ-B was 30 ?,and the optimum pH was 7.2,during its growth and degradation of lignin.When the initial concentration of lignin was 0.2% in the medium,the highest degradation rate and decolorization rate were observed,achieving 52.22% and 51.26%,respectively.For bacterial consortium NyZ-S,the optimum temperature for degrading lignin was 20 ?,and the optimum pH is 7.2.When the lignin concentration in the medium increased from 0.2% to 0.4%,the degradation rate and decolorization rate also increased.It reached the maximum(17.02% and 22.24%,respectively)when the lignin concentration was 0.4%.The salt concentration in the medium had an obvious effect on the growth and degradation of both bacterial consortium NyZ-B and bacterial consortium NyZ-S.The degradation of the bacterial consortia showed a downward trend with the increase of salt concentration in the medium.The activity of the lignin degrading enzyme was also detected in the two bacterial consortia.The lignin surface morphology changes caused by the degradation of lignin by two bacterial consortia were identified by scanning electron microscopy,and the intermediate products of lignin metabolism by two bacterial consortia were identified by gas chromatography/mass spectrometry.Finally,based on the Illumina HiSeq sequencing platform,the microbial diversity of the two bacterial consortia were analyzed.The most abundant species in the bacterial consortium NyZ-B were Halomonas sp.and Marinobacter sp.,and the most abundant species in bacterial consortium NyZ-S were Halomonas sp.and Pseudomonas sp.In the process of growth and cinnamic acid degradation of Rhodococcus sp.NyZ306,the optimum temperature is 20 ?,and the optimum pH is 6.2.When the initial concentration of cinnamic acid in the medium was higher than 2 mmol/L,Rhodococcus sp.NyZ306 took a certain adaptation period before its degradation of cinnamic acid.And the higher the concentration of cinnamic acid was,the longer the adaptation period occurred for strain NyZ306.The salt concentration in the medium had an obvious effect on the degradation of cinnamic acid,and the degradation rate showed a downward trend with the increase of salt concentration in the medium.The intermediate metabolites of cinnamic acid degradation were detected by high performance liquid chromatography and ultra-high-performance liquid chromatographyquadrupole time-of-flight mass spectrometry,and their possible metabolic pathways were deduced based on relevant literatures and detected metabolites.At present,there is few reports about microorganisms from the ocean that could grow with lignin or cinnamic acid as the sole carbon source.This study studied the degradation pathways of lignin and cinnamic acid,and enriched the marine microbial strain resource pool in China.This has laid a theoretical foundation for further research on the degradation of microbial-driven aromatic compounds in offshore waters and will also help to reveal the material circulation involved.