Bacteria Taxonomic Diversities And Functional Profiles In Estuarine Wetland

Bacterial community in estuarine sediments is the key microorganisms mediating material circulation and energy metabolism,which is important for maintaining the stability of estuarine ecological function.It is significance to study the ecological and metabolic processes,bacterial community diversity and regulating factors in estuarine and coastal areas.Estuarine and coastal zones of China span multiple climatic zones and affected by human activities,tidal movement and salt marsh vegetation.At the same time,there are obvious gradients of environmental factors in the estuarine and coastal areas,such as temperature gradient,salinity gradient and nutrient gradient.These largescale and local environmental characteristics significantly affect the diversity and ecological functional characteristics of bacterial communities in estuarine and coastal ecosystems.However,there is still a lack of in-depth research on the bacterial communities diversity and functional characteristics in estuarine and coastal environments.This study selected 10 typical estuaries along China's coastal zone as the research areas to explore the diversity,structural composition,community construction mode and ecological function characteristics of sediment bacterial communities on a large spatial scale.The effect of salinity gradient on bacterial community was also studied in the Yangtze Estuary and its adjacent area.In addition,taking Chongming Dongtan salt marsh as the research area,to examined the impact of salt marsh plants on bacterial diversity and function.This research enrichs the theoretical understanding of microbial ecology in the estuary and coastal environments,and can provide a scientific basis for the protection of ecological environment in the estuarine and coastal areas.The main results are as follows:(1)Based on the macrogenomic sequences and 16 S rRNA gene,the taxonomic composition,community construction process and ecological function of bacteria in the surface sediments from estuarine and coastal intertidal zones of China were studied on the latitudinal gradient.The results showed that there was an obvious temporal and spatial dynamic pattern of bacterial community structure,which was closely related to the physichemical properties of sediment,such as sediment temperature,p H,salinity and ammonia nitrogen.The construction process of bacterial community was affected by both stochasticity and determinism processes.Dispersal limitation was the main factor affecting the seasonal and spatial variations of community diversity,which explained 59.51% of the overall variation of bacterial community,followed by variable selection,which explained 36.79% of the overall variation of bacterial community.The results of metagenome sequences showed that the seasonal variation of functional characteristics of bacterial community was not significant,but showed significant spatial differences.Pearson correlation analysis showed that climate factors significantly affected the functional characteristics of bacteria in China's estuarine and coastal sediments.(2)Based on the related functional genes of bacterial community,the potential metabolic pathways of C,N and S elements in bacterial community were constructed.The results showed that there was a close correlation between the functional genes that mediate the circulation of key elements such as C,N and S,and there was flexible connectivity in metabolic pathways,which is of great significance to maintain the element circulation of estuarine and coastal ecosystems.The potential bacterial groups that dominate the circulation of key elements such as C,N and S were related to the characteristics of sediment functional genes,but were weakly affected by sediment environmental factors.These correlations indicated that there was a certain stability in the structure and functional characteristics of bacterial communities mediating the circulation of key elements in estuarine and coastal sediments.The research results revealed the classification and functional characteristics of bacterial communities in China's estuarine and coastal sediments under the latitudinal gradient,and clarified the impacts of environmental and climate change on estuarine and coastal ecological health and bacterial microbial diversity and function.(3)Based on 16 S rRNA gene and macrogene data,the community structure and functional characteristics of bacteria under the salinity gradient of the Yangtze River Estuary and its adjacent areas were discussed.Results showed that the variation of bacterial community structure was significantly related to salinity,nitrite,ammonium nitrogen,ferric iron,total organic carbon and moisture content.In addition,the results also showed that the diffusion restriction in estuarine and coastal sediments also affected the assembly process of bacterial community.In this geographical range,the stochasticity process was the main process affecting the construction of bacterial community,which explained about 60% of the community variation.Our result showed that the structural variation of bacterial community was not only directly regulated by the deterministic process mediated by environmental factors,but also affected by the stochastic process mediated by spatial distance.(4)Based on 16 S rRNA gene and metagenomics data,the ecological functions of sediment bacterial communities were analyzed in the Yangtze River Estuary and its adjacent areas.The results showed that there was an obvious spatial pattern of C,N and S cycle functional genes driven by bacterial community under the salinity gradient,suggesting the key regulatory role of salinity on the geochemical function of environmental microorganisms.The results of microbial flora annotation analysis showed that Desulfobacteraceae,Gemmatimonadacea,Rhodospirillacea,Chromatiacea,Rhodobacteraceae,Ecotothiorhodospiraceae,Pseudomonadacea and Nitrospiraceae are potential key microorganisms driving the coupling of C and N cycles,and can be used as marker microorganisms for the functional health and stability of estuarine and coastal ecosystems.(5)Based the qualitative and quantitative analysis of N-acyl homoserine lactones(AHLs),the compositions of AHLs in intertidal wetlands and their potential role in the element circulation were discussed.Our results showed that the content of AHLs in rhizosphere sediments was higher than that in non-rhizosphere sediments,which was significantly correlated with sediment organic carbon and p H.C6-HSL,C8-HSL,C10-HSL and C12-HSL were the common quorum sensing signal molecules in intertidal sediments.Rhizosphere sediments had higher AHLs concentration than nonrhizosphere sediments,and affected sediment bacterial diversity,community function and element cycle.Bacterial diversity and ecological function were regulated by AHLs.Isotope-labeling experiments also showed that C6-HSL,C8-HSL and C12-HSL in intertidal sediments play an important role in nitrogen transformation processes such as nitrification,denitrification and anaerobic ammonia oxidation.The results of this study also reflect the impact and potential regulation mechanism of tidal salt marsh plants on the structure and functional characteristics of bacterial community,and improve the understanding of the ecological and physiological characteristics of bacterial community in estuarine tidal wetlands.