Bacterioplanktonic Community's Structure And Their Influencing Factors In The Pearl River Estuary

Planktonicbacteria play an extremely important role in the biogeochemical cycle of aquatic ecosystems.The planktonic bacteria are the key link in the material and energy cycle system in the estuarine water ecosystem.The Pearl River Estuary?112.5-114.5°E,21.5-22.4°N?is ocated in the heart of Guangdong–Hong Kong–Macau Greater Bay Area,in which the water ecological health and safty is seriously deteriorated by industrial and agricultural developments,as well as rapid urbanization.The key to keep the safety of estuary ecosystem and the protection and utilization of fishery waters is grasp the characteristics of their material cycle energy cycle.In view of the fact that planktonicbacteria can respond to changes in physical and chemical conditions of water environment,the dynamic changes of bacterial community structure can reflect the health and safety of aquatic ecosystems.Therefore,in order to understand the dynamic changes of planktonicbacterial communities in the Pearl River Estuary,the response patterns to environmental factors and the remediation potential of planktonicbacteria on aquatic ecosystems are explored and further developed.The Pearl River estuary was used as the research area,and the planktonicbacteria were used as research objects to study the community structure and analyze its relationship with environmental factors.In this study,we collected surface water samples?0.5 m depth?from the Pearl River Estuary?112.28?113.65°E,22.20°N?22.79°N?in August 2017?summer?,November 2017?autumn?,January 2018?winter?and May 2018?spring?,using high-throughput sequencing of 16S rDNA gene amplicons based on the Illumina Miseq platform,coupled with multivariate bioinformatic and statistical analyses,to investigate the bacterioplanktonic community?s composition and their environmental impact factors in the Pearl River Estuary.During the study period,the annual water temperature of the Pearl River Estuary range from19.20°C to 29.20°C;the salinity of the water was generally lower than 1‰in spring and summer,and the average salinity in autumn and winter was 5.63‰and4.37‰respectively;the pH of was at fluctuation between 7.37 and 8.56,the redox potential fluctuated?ORP?between 34.73 and 53.84 mV;the total dissolved solids?TDS?showed a decreasing trend during the survey period;the dissolved oxygen?DO?in summer water was lower than the other three seasons.The total phosphorus?TP?in the water body of the Pearl River estuary is in the class III-IV level of surface water quality standard?GB3838-2002?,and the total nitrogen?TN?is in the V class or the inferior V class.The concentration of phosphate(PO₄^3-),nitrate?NO₃^-?,nitrite?NO₂^-?,ammonia?NH₄⁺?,and silicate(SiO₃^2-)in the Pearl River Estuary fluctuated with seasonal changes.The analysis of the environmental conditions of the Pearl River estuary shows that the summer environmental conditions are significant different from other seasons.The environmental similarity between Hongmen and Jiaomen is the highest,and the environmental difference between Humen and Yamen is the largest.A total of 14 classes and 24 genera were detected in the estimatum of the Pearl River Estuary.?-Proteobacteria?29.69%?,?-Proteobacteria?12.30%?,?-Proteobacteria?9.88%?,Actinobacteria?8.17%?and Bacteroidia?6.82%?were abundant classes in Pearl River Estuary.Pseudomonas?2.15%?,hgci_clade?4.48%?,Flavobacterium?3.17%?,Limnobabitans?2.69%?,Acinetobacter?3.50%?,Cl500-29_marine_group?3.13%?were dominant taxa at genus levels.The community diversity analysis found that the Simpson index of summer bacterial community was significantly lower than other seasons,but there was no significant difference in the Shannon index of all samples.UPGMA analysis based on Bray-Curtis difference coefficient showed that the summer's planktonicbacteria community in the Pearl River estuary was divided into a group,which was significantly different from autumn,winter and spring.This result is consistent with the results of environmental grouping,indicating that the planktonicbacteria community is related to the environment.ANOSIM analysis showed that there were significant seasonal differences in the planktonicbacterial communities in the Pearl River Estuary?R=0.88,P<0.01?,and there was no significant spatial difference?R=-0.21,P=1?.There was a significant difference in the planktonic bacterial community between the Pearl River network and the Pearl River estuary in January 2018?winter??R=0.98,P=0.001?.RDA?Redundancy analysis?results showed that bacterioplanktonic community composition was significantly influenced by TDS?r²=0.8576,P<0.01?,temperature?r²=0.6935,P<0.01?,pH?r²=0.4709,P<0.01?,DO?r²=0.3464,P<0.01?,NO₃^-?r²=0.3062,P<0.01?,PO₄^3-?r²=0.2892,P<0.01?,TN?r²=0.2176,P<0.05?,NO₂^-?r²=0.4460,P<0.01?and SiO₃^2-?r²=0.2535,P<0.05?in the Pearl River Estuary.Pearson analysis results revealed that a significant negative correlation between the relative abundances of dominant taxa and temperature as well as TDS,whereas salinity,pH,DO and SiO₄^2-showed significant positive correlation with the relative abundances in predominant taxa.The rainfall is large and seasons wind is frequently are important characteris in the Pearl River Estuary in summer,there are driving the severe and continuous changes in the physical and chemical characteristics of the water are the main reasons for the significant differences in the planktonic bacterial communities in summer.The increase in temperature under natural conditions is conducive to the growth and reproduction of planktonicbacteria.This is contrary the conclusion of this study.To the fact that under the unique environmental conditions of the Pearl River Estuary,the influence of single environmental factors on planktonicbacteria is insufficient to explain the environment.Dynamic changes in the community of planktonic bacteria.