Spatial Distribution、Community Structure And Predictive Functional Analysis Of Bacterioplankton In Seawater Of The Northern Beibu Gulf In Summer

Bacterioplankton is an important part of marine microbial ecosystems and plays an irreplaceable role in biogeochemical cycles,ecological processes and ecosystems.The Beibu Gulf has rich plankton resources and high diversity,and is an important area for studying bacterioplankton.However,there are very few studies on bacterioplankton in the Beibu Gulf.In addition,the marine environment is facing increasingly severe pollution pressures.Bacterioplankton can indicate environmental conditions.Therefore,long-term monitoring of bacterioplankton in the Beibu Gulf is of great significance.In this study,from July 2020 to August 2020,50 sampling stations were set up to collect seawater samples in the northern waters of the Beibu Gulf,and flow cytometry was used to study the spatial distribution of bacterioplankton and the influencing factors of abundance.According to the type of human activity,9 sampling stations were set up to collect filter samples.High-throughput sequencing technology and PICRUSt software were used to study the community structure and influencing factors of bacterioplankton and predict their ecological functions combined with bioinformatics methods.The bacterioplankton abundance in the horizontal direction showed a decreasing trend from coastal areas to deep sea areas.There was no obvious vertical trend in the bacterioplankton abundance in the coastal waters.The abundance in surface layer and middle layer in the in the offshore water were close.There are obvious stratifications in the vertical direction in the offshore waters,the abundance in bottom layer was higher than that in surface layer and middle layer.The abundance of bacterioplankton is controlled by the cumulative interaction between physical and chemical parameters and environmental factors such as nutrients,instead of being controlled by a single factor.Different water layers have different control factors for the abundance of bacterioplankton.Pearson correlation analysis showed the abundance in surface layer had significantly negative correlations with salinity and p H(P<0.05),significantly positive correlations with phosphate、ammonium、silicate(P<0.05)and very significantly positive correlations with nitrate,nitrite(P<0.01);the abundance in middle layer had very significantly positive correlations with temperature and phosphate(P<0.01),significantly positive correlations with nitrate、nitrite(P<0.05)and significantly negative correlations with ammonium(P<0.05);the abundance in bottom layer didn’t show significant correlation with various environmental factors.A total of 65 phyla and 1186 genera were detected in Seawater of the northern Beibu Gulf in summer.The dominant bacterial groups are Proteobacteria,Cyanobacteria.43phyla and 592 genera were detected in areas affected by industry and fishery.The dominant phyla are Cyanobacteria,Actinobacteriota,and Proteobacteria,and the dominant genera are Cyanobium PCC-6307,Ilumatobacteraceae＿uncultured,Chloroplast＿norank.54 phyla and 1,001 genera were detected in areas mainly affected by fishery.The dominant phyla are Proteobacteria、Actinobacteriota、Cyanobacteria,and the dominant genera are Cyanobium PCC-6307,Ilumatobacteraceae＿uncultured,Synechococcus CC9902.58 phyla and 687 genera were detected in areas not affected by industry and fishery.The dominant phyla are Proteobacteria、Chloroflexi、Desulfobacteriota,and the dominant genera are Anaerolineae＿norank,SZB7＿norank,Syntrophobacterales＿norank.αdiversity found that there are differences in species richness and diversity in different areas.The higher the pollution degree is,the lower the species richness and diversity are.βdiversity shows that due to the impact of different human activities in different regions,there are differences in the structure of the planktonic bacterial community.RDA analysis shows that p H is the most significant environmental factor(r~2=0.80),phosphate(r~2=0.53),salinity(r~2=0.45),dissolved oxygen(r~2=0.35),nitrate(r~2=0.30),nitrite(r~2=0.45),and silicate(r~2=0.52)also affect the community structure of bacterioplankton.Kyoto Encyclopedia of Genes and Genomes(KEGG)predicted 6 types of biological metabolic pathways and 41 sub-functions of bacterioplankton,showing the richness of functions.The main functions of bacterioplankton in different pollution levels are consistent,but the abundance is different.The higher the pollution degree is,the greater the main function abundance is.Furthermore,the data of KEGG Orthology(KO)was compared with the orthologous genes in the KEGG database.The predicted ko data contained 42 genes related to nitrogen metabolism and 55 genes related to photosynthesis,indicating that there are abundant nitrogen metabolism and photosynthesis pathways in seawater of the northern Beibu Gulf in Summer.There are differences in the abundance of nitrogen metabolism and photosynthesis genes in different regions.This difference is related to the degree of water pollution.The higher the degree of pollution,the higher the gene abundance.