Microbial Community Structure In Seamount And Diversity Of Marine Magnetotactic Bacteria

Seamounts are undersea mountains rising abruptly from the sea floor,but still below the sea surface.Seamounts are one of the common landforms on the seabed and distributed at different depths around the world ocean.Seamounts can interact dynamically with underwater currents.Seamount ecosystems have high biodiversity and specificity,should also be rich in microbial resources.However,compared with other oceanic ecosystems,very limited information of microorganism is available concerning seamount habitats.So far,only a few literatures have reported microbial diversity in the seamount region,involving only a few dozen seamounts,and most of them are concentrated in the hydrothermal system of the seamount.Information on the diversity and community structure of seamount microbes is extremely limited compared with other oceanic ecosystems.They represent unique biological habitats with various microbial community structures.Study of the microbial community and diversity in seamount ecosystems may provide a better understanding of their ecological functions.To extend our knowledge of seamount habitat,we performed an integrated study on population structure and the occurrence of bacteria and archaea in sediments from a seamount of the Mariana Volcanic Arc,in the tropical western Pacific Ocean.After DNA extracted from the sediments,16S rRNA gene were amplificated using universal primers of bacteria and archaea.Then,diversity and communities of bacterial and archaeal were investigated by using high-throughput sequencing.We found,the bacterial community diversity occurred on the top of the seamount,and the highest community complexity decreased significantly with the increasing depths of the sampling stations.The seamount bacterial community was mostly consisted of Proteobacteria,and Proteobacteria dominant at 13 of 14 stations,but ranked second in abundance to members of the phylum Firmicutes at the deep-water station located on a steep slope facing the Mariana-Yap Trench.The bacterial community structure of the seamount sediment is mainly divided into three main clusters.The difference in bacterial community structure may be caused by geographical location and environmental factors,but nothing to do with the water depth.Interestingly,the station on the steep southeast slope,facing the Mariana-Yap Trench,is rich in minerals and has different community composition compared to other stations.The geographic properties of the seamount seem to be important in shaping the population structure of the distinctive bacterial communities.The diversity and distribution of archaea in seamount is consistent with that of bacteria.The archaeal community diversity and species richness were greatest at stations near the top of the seamount,and lowest at the deepest station.The results indicated that Nitrosopumilales belong to Phylum Thaumarchaeota was the dominant clade at all 14 sample stations.Similar to bacteria,community composition analysis indicated that stations at different depths and locations had different archaeal community structures,and one sample station on the steep southeast slope that faced the Yap-Mariana trench had a unique composition of Achaea,with a higher abundance of Candidatus Nitrosopumilus.The archaeal communities were grouped into three main clusters,and there is a clear transition of archaeal community composition as a function of water depth in this seamount.Water depth and geographic variables seemed to be important in shaping the distinctive archaeal communities.In summary,we reported the first systematic analysis of bacterial and archaeal community structure in the unique seamount habitat.Together the results obtained indicate that,geographic properties and water depth of the seamount stations are important in shaping the bacterial and archaeal community composition,and they may explain the unique distribution patterns of bacteria and archaea in this seamount.This study provides a foundation for future research on microbial communities,biogeography,functions,and evolution in seamounts,and the unique distribution patterns also shed light on the ecological functions of microorganism in seamounts.Magnetotactic bacteria?MTB?consist of special microorganisms that can swim along the magnetic field,which can orient and navigate along geomagnetic field lines.MTB contain intracellular membrane-bounded,nano-sized,and single-domain crystals,called magnetosomes,which mainly consist of iron oxide?magnetite,Fe₃O₄?or iron sulfide?greigite,Fe₃S₄?.Magnetosome formation is a genetically controlled process,and the magnetic crystals display species-specific morphologies and exhibit specific arrangements within the cell.Magnetosomes arranged in a chain result in a magnetic dipole moment of cells,which enables them to align and swim along geomagnetic field lines and migrate to the oxic-anoxic interface in chemically stratified sediments of freshwater or marine environments.So,magneto-aerotaxis and magnetosome synthesis are the two most important features of magnetotactic bacteria.Magnetotactic bacteria are ubiquitous in water columns and sediments of freshwater,brackish,marine and hypersaline habitats.They are believed to play an important role in the biogeochemical cycle of iron,nitrogen,sulfur,carbon and other elements.Magnetotactic bacteria are a morphologically,phylogenetically and metabolically heterogeneous group of prokaryotes.They are diverse in morphology,including cocci,rod,spirilla,vibrio and multi-cell from?multicellular magnetotactic prokaryotes?.Based on the sequences of their 16S rRNA genes,the MTB have been phylogenetically affiliates into the Alphaproteobacteria,Deltaproteobacteria,Gammaproteobacteria,and Nitrospirae phylum,or the candidate division OP3.Previous studies have also indicated that MTB belonging to the class Alphaproteobacteria dominate in environments where MTB occur.Through research and analysis,it is found that the high-throughput sequencing method is superior to the traditional method in the diversity and phylogenetic analysis of magnetotactic bacteria.To assess the diversity and geographic distribution of magnetotactic bacteria,high-throughput sequencing method was applied to analysis of biogeographic distribution of magnetotactic bacteria in seveal different marine habitats.We detected magnetotactic bacteria in the sediments of East China Sea continental shelf,Antarctic and Arctic aera,the Okinawa Trough,the eastern Pacific Ocean,and other special marine habitats,such as hydrothermal fluid and seamount.The highest relative abundance of magnetotactic bacteria is 3.5%.Except for common marine magnetotactic bacteria groups,such as magnetospirillum,magnetococcus,magnetovibrio,a large number of magnetotactic bacteria belonging to Nitrospiare phylum were discovered in different marine environment,which were found previously only in freshwater environments.Also,multicellular magnetotactic prokaryotes,which found only in the coastal environment such as intertidal zone and lagoon,were found in ocean and hydrothermal environment.Phylogenetic analysis of16S rRNA gene sequences of identified Nitrospiare magnetotactic bacteria showed,marine magnetotactic bacteria belonging to Nitrospiare were seprated from that from freshwater environments,indicating marine and freshwater groups might have different origin and evolution history.Similarly,the multicellular magnetotactic prokaryotes in the hydrothermal environment have different origins from the known species found in the intertidal and lagoon sediments.The branch is located at the root of the phylogenetic tree,indicating they might be an ancient species of multicellular magnetotactic prokaryotes.In summary,we found magnetotactic bacteria in several different marine environments by using high-throughput sequencing of 16S rRNA gene amplicon.We have got more knowledge of biogeographic distribution characteristics of marine magnetotactic bacteria,and it will lay theoretical foundation for application and resource development of marine magnetotactic bacteria.Nitrospiare magnetotactic bacteria and multicellular magnetotactic prokaryotes were found in the hydrothermal sediment environment for the first time,which provided a new basis for fully understanding the evolutionary origin of these two special kinds of magnetotactic bacteria.We will undertake studies to gain more knowledge of the diversity,biogeography,and evolution of magnetotactic bacteria in marine ecosystems.