Spatial And Temporal Variation Of Microbial Community Structure In The Bohai Sea And Its Response To Environmental Pressure

Due to their unique ability to decompose and mineralize of dissolved organic matter,marine microorganisms are considered to be important regulatory factors in the global element cycles.The microorganisms in these surface waters show an obvious global seasonal succession pattern,they are subject to some physical and chemical factors such as illumination,climate change and nutrient salt load,etc.These factors will be determined by the latitude changes and the distance from the offshore.In addition,we found that the microbial community structure showed different relationship with environmental factors in different areas,mainly include microbial interactions,virus infections and environmental stresses.Therefore,the interaction and scale between factors will ultimately determine the survival advantage of a particular species.It will be helpful to interpretate the survival mode of microorganisms in a particular environment,the relationships between microorganisms and specific environmental factors and how microorganisms respond to the environmental factors by surveying the distribution of microbial community and its response to the environmental stress.(1)To study the distribution characteristics and community structure diversity of microorganisms in four seasons of the Bohai Sea,we used flow cytometry to measure the abundance of picoplankton,and high-throughput sequencing technology to analyze the composition of microbial community structure with seasonal variation.It was demonstrated that the abundance distribution and diversity of microorganism showed obvious seasonal difference.The average abundance of virioplankton was spring>autumn>summer>winter,the average abundance of bacterioplankton was spring>autumn>summer>winter.Spearman correlation analysis showed that there were significant correlations between temperature,salinity and virioplankton,bacterioplankton.By comparing the microbial composition between summer and winter,it was found that the differences between species composition were obvious,and among all of them,temperature and the concentration of ammonium played a decisive role.(2)By studying the microbial composition and its driving factors,it was found that the differences were significant.The average abundance of Proteobacteria in the Bohai Bay was 39.8%,in the Liaodong Bay was 37.8% and in the Laizhou Bay was 59%.By analyzing the microbial diversity index we found that the distribution of species diversity was Laizhou Bay > Bohai bay > Liaodong bay.The dominant species in each transect are Proteobacteria,Bacteroidetes,Cyanobacteria,Actinobacteria,Planctomycetes.There is a significant correlation between the microbial distribution and the location,the concentration of phosphate and the concentration of nitrate.(3)It was found that there were significant differences between virioplankton and bacterioplankton abundance during summer and winter in the impact of temperature and riverine input.In summer,the abundance of virioplankton and bacterioplankton showed a higher trend far the estuarine area,and showed a lower trend near the estuarine area.While in winter,the results are opposite.The diversity index was slightly higher in winter than in summer.There were significant differences in species composition between the two groups(P<0.05),and the species with significant difference were Cyanobacteria,Sphingobacteriia and Actinobacteria.(4)The changes of microbial community structure diversity before and after petroleum hydrocarbon pollution repair in 19-3 oil spill platform were further analyzed.Both the abundance of virioplankton and bacterioplankton presented a decreasing trend after the pollution repairment.And there were significant differences in the composition of the species before and after the treatment of petroleum hydrocarbon pollution.After petroleum hydrocarbon pollution was repaired,both Planctomycetes and Thaumarchaeota were significantly increased in the phylum level.In the genus level,the relative abundance of Nitrosopumilus significantly increased,and Synechococcus and Formosa tended to decrease.Also there were significant relationships between VBR and microbial community compositions by the network analysis.It is suggested that the virioplankton may play an important role in controlling the distribution of bacterioplankton in the process of petroleum hydrocarbon pollution repair.(5)In view of the influence of water environment change on the Bohai sea,we studied the influence of the Yellow Sea Warm Current on the microbial community structure in the Bohai sea.We found that the water temperature and salinity in the northeast of Bohai Sea was much higher than the southwest due to the impact of the Yellow Sea Warm Current.The abundance of virioplankton and bacterioplankton also showed a significant trend of high east and low west.The diversity distribution showed that it was much higher in the eastern region than the western region during winter.The proportion of Cyanobacteria in the three groups was Group 1:10.6%,Group 2:14.5%,Group 3:16.1%,respectively,which showed a significant low trend of east and high trend of west.The correlation analysis showed that the temperature is the main factor affecting the distribution of virioplankton and bacterioplankton.The concentration of nitrate and the concentration of phosphate have an important influence on the species composition.