Diversity And Spatiotemporal Distribution Of Bacterioplankton And Pathogens In Luanhe Estuary

Planktonic bacteria and their subgroups affect the ecological balance profoundly and serve important functions in the estuarine waters.Particularly,the pathogenic bacteria can contaminate near-shore water bodies and aquaculture areas,leading to the outbreak of aquatic diseases,endangering economic development and human health.In this study,the abundance of planktonic bacteria(HNA and LNA subpopulations),their community structure,driving factors,and the spatial and temporal distribution of several common pathogenic bacteria in the Luanhe River Estuary were investigated.This study aims to improve our knowledge of the estuarine microbial ecology which would ultimately help to protect and utilize the ecological resources of the estuary.The average abundance of planktonic bacteria in July,September,March,and May were 2.12×10~7 cells/ml,3.69×10~6 cells/ml,7.14×10~5 cells/ml,and 3.19×10~6 cells/ml,respectively.The abundance of planktonic bacteria,their subpopulation,and the proportion HNA subpopulation showed significant differences across time(P<0.001)but not space.The HNA subpopulation was the dominant population in the Luan River Estuary.The proportion of the LNA subgroup in May was higher,which dominated the changes of the planktonic bacterial community.The response and sensitivity of the two subgroups to environmental changes were different.The HNA subgroup responded more strongly to climate change,and the LNA subgroup responded positively to spring phytoplankton outbreaks.The changes in the abundance of planktonic bacteria and their subgroups were mainly controlled by temperature and nitrogen or phosphorus nutrients.High-throughput sequencing results showed that the planktonic bacterial community in the Luan River Estuary belonged to three groups:Proteobacteria(46.8%),Bacteroides(25.4%)and Cyanobacteria(18.3%).There was a significant difference in the composition of the community and the dominant population in March and July,but there was no significant difference in species richness and diversity.The spatial difference in the community structure in March was small but large in July,which indicated the possible effect of river flow on the structure and diversity of planktonic bacteria.In addition,the environmental factors affecting the structure of planktonic bacteria were chlorophyll a,dissolved oxygen,total nitrogen,total phosphorus,and nitrite.Particularly,Cyanobacteria had significant positive correlation with nitrogenous nutrients and dissolved oxygen,Actinobacteria was positively correlated with nitrogenous nutrients,both Chloroflexi and Verrucomicrobia were positively correlated with total phosphorus,and Bacteroides was mainly affected by chlorophyll-a.The abundances of Escherichia coli,Enterococcus,and Salmonella in the Luan River Estuary were high but of Staphylococcus aureus and Vibrio parahaemolyticus were low.The seasonal changes in the abundance of the five pathogens were not significant;however,the spatial variations in the abundance of Escherichia coli,Vibrio parahaemolyticus and Salmonella showed a significant decrease from the estuary to the far shore.This indicated that large populations of Escherichia coli,Vibrio parahaemolyticus,and Salmonella enter the sea through the human activity.Thus,monitoring and control of living waste should be strengthened near the Luanhe River Estuary.