Distribution Of Petroleum Hydrocarbons And Variation Of Microbial Communities In Sediments From Dalian Sea Area

Marine sediments contain most of pollutants,in which the microbial communities are abundant,and they are playing a significant role in material circulation.DayaoBay is located in the northwest of Yellow Sea.This study was focused on studying 50 samples of 10 stations in Dayao Bay from year 2011 to 2015.The total amount of straight-chain paraffin,UCM content and total amount of polycyclic aromatic hydrocarbon showed an increasing trend from 2011 to 2014 and a decreasing trend in 2015.From the ratios of the comprehensive isomer of polycyclic aromatic hydrocarbons,we can certify that the petroleum pollution mainly originated from combustion of petroleum and petroleum.The RI value of heavy metal comprehensive index was raised from 2011 to 2014 and reached“high ecological risk”in 2014,but the mean RI value of all stations was 388.5 in 2015.Pearson correlation analysis,cluster analysis and principal component analysis showed that Cr and Co may from petroleum pollution,while Pb,Ni and As also partially came from petroleum pollution.Through high-throughput sequencing,only 10188-51578 effective sequences were obtained from samples.All sequences belong to 59 phyla,152 classes and 1381 genera.As bacterial community analysis at phylum,class and genus level,the community structure was similar between 2011 to2013,and 2012to2014,which was much different from that in 2015.From year 2011 to 2014,Proteobacteria was the phylum with the highest abundance?over 70%?,but its abundance decreased in all stations in 2015,with a mean value of 52%.However,the abundances of Firmicutes,Bacteroidetes and Planctomycetes were considerably higher than that of the previous 4 years.At class level,the abundance of Gamma-proteobacteria and Deltaproteobacteriaremained high in all samples,and the abundance in 2015 were only22%and 21%,respectively,which were at least 30%in the previous 4 years.RDA results showed that40.67%of community structure variations were related to straight-in paraffin,higher than the 34.32%of polycyclic aromatic hydrocarbon and 33.27%of metal ion as well as other physical and chemical parameters.Co,Fe,3br,Phe,Ph,Pr,C_odd and C₁₆ were significantly?p<0.01?related to the bacterial community structure while V,Ace,Ant,Tpahs,2br,F and C₁₄₃₅ were significantly related to the bacterial community structure?p<0.05?,indicating that these environmental factors were the main driving factors of community structure variations.In order to explore the relationship between bacterial community and petroleum pollution,Pr,Ph,C₁₆,C₁₄₃₅,C_odd,3br,F,Phe and Tpahs were used as indicators in this study,and five stations in 2012,2014 and2015 were selected as a heavy pollution group?H?,a light pollution group?L?,and a moderate pollution group?M?.RDA and Mantel analysis showed that environmental factor matrix was significantly related to the bacterial community matrix,and the grouping was confirmed reasonable according to the similarity analysis of non-parametric testing.At genus level,42 dominant genera exhibit significant differences.Correlation thermal analysis and RDA showed that petroleum pollution indicators were positively related to25 genera,including 20 genera belonged to Proteobacteria,such as Haliangium and Arcobacter,and negatively related to another 17 genera,including Faecalibacterium and Streptococcus belonged to Firmicutes.Of all predicted functional genes,only 8.6%of pathways,most of which were metabolisms witnessed significant differences among the three groups.Carbohydrate metabolisms like galactose metabolism have increased significantly in group L.COG analysis also indicated that group L was higher?about 12%?than H and M only in carbohydrate transportation and metabolism?G?.Additionally,most polysaccharides metabolism-related pathways such as lipopolysaccharide biosynthesis in 2015_L was 12%lower than that in the other two groups.Four groups of different petroleum hydrocarbons were added into sediments to enrich and isolate indigenous petroleum degrading strains.A total of 307 petroleum hydrocarbon degrading strains were obtained,which belonged to 4 phyla,6 classes,36 genera and 77 species.The strains isolated from crude oil were the most abundant.The maximum strains?138 strains?belonged to Gammaproteobacteria.As well as strains that can degrade petroleum,straight-chain paraffin and polycyclic aromatic hydrocarbons as substrates.The petroleum degradation rate of strain Ochrobactrum cytisi AH07 was up to 70%,and combined strains could significantly increase the degradation rates of petroleum,and the addition of plant polysaccharides could greatly improve the degradation rate of petroleum.Petroleum pollution increased from year 2011 to2014,and affected the bacterial communities in situ.Activation of polysaccharides metabolism pathways could effectively promote the petroleum degradation,which indicated that bacteria can adapt to a petroleum pollution environment,and the environment also screened the bacteria that can be alive.However,the changes of bacterial community in 2015indicated that this area was in the process of ecological restoration,in whichmore new species appeared at phylum,class and genus level.The increased species diversities,the variation of bacterial communities and the difference of corresponding functions also demonstrated the driving effects of environmental factors.