Diversity Of Cultivable Bacteria And The Community Structure And Biogeographical Distribution Of Bacteria And Archaea In Magellan Seamount

Seamounts are submarine mountains rising from the ocean seafloor but having their summits below the surface of the water.They are important parts of the marine ecosystems due to their tremendous amounts,extensive distribution,unique topographic structures,complex hydrological environments and hydrothermal vents.Seamounts are excellent "natural laboratories" for studying marine microbial ecology,evolution and biogeographical distribution.Studies on microorganisms living in some extreme(such as high pressure,low temperature,high temperature or high salinity)environments around seamounts represent one of the frontiers and focuses in the field of marine microbiological researches.However,there is still a lack of researches on the effects of the changes in marine dynamics and nutrient distribution caused by seamounts on the microbial community structure and biogeographical distribution.The thesis takes Magellan Seamount as the research area and studies the cultivable bacterial diversity,the community structure and biogeographical distribution of bacteria and archaea in this area by culture and high-throughput sequencing methods.The results of high-throughput sequencing analysis of bacteria in seawater samples showed that the diversity of the bacterial communities firstly increased and then decreased with the increase of the water depth.The relative abundance of cyanobacteria(60.6%)was the highest in upper seawater,but proteobacteria(46.6%)were the most abundant on the whole.Furthermore,in proteobacteria,the relative abundance of ?-proteobacteria was the highest,and their abundance increased with the water depth;the relative abundance of a-proteobacteria was the secondly highest but no significant relationship was found between their abundance and the water depth;the relative abundance of ?-proteobacteria increased first and then decreased with the water depth while that of ?-proteobacteria basically increased with the water depth.Comparative analysis of the community structure compositions,NMDS analysis,UPGMA cluster and ANOSIM analysis all showed that the bacterial community structures at same depths(1000 m,2000 m and 3000 m)of different sites of the Magellan Seamount area were significantly different.Bacterial strains were isolated from the seawater and other kinds of samples collected from the Magellan Seamount area using the dilution plate technique on agar plates containing six different media.Totally 378 strains including 285 ones from seawater and 93 ones from other kinds of samples were obtained and their 16S rRNA gene sequences were further determined.The 16S rRNA gene sequence analysis revealed that these cultivable bacteria belonged to forty-one genera in four phyla.Further analysis showed that the community structure of cultivable bacteria in seawater samples was quite different from that in other kinds of samples:?-proteobacteria(44.2%)were most abundant,and the dominant genera were Alteromonas,Planococcus and Bacillus in seawater;while ?-proteobacteria(41.9%)were most abundant and the predominant genera were Brevundimonas,Pseudomonas and Rhodococcus in other kinds of samples.In addition,a total of 12 bacterial strains sharing less than 98.5%16S rRNA gene sequence similarities to known bacterial species and hence possibly representing new species or genera were obtained,accounting for 3.2%of the total numbers of the isolated bacterial strains.The results of high-throughput sequencing analysis for archaea in seawater samples showed that,like bacteria,the diversity of the archaeal communities firstly increased and then decreased with the increase of the water depth.The relative abundance of archaea belonging to the phylum Euryarchaeota decreased with the water depth;on the contrary,the relative abundance of archaea belonging to the phylum Thaumarchaeota increased with the water depth.Further analysis showed that there was little difference in the archaeal community structures in samples collected at the same depths of different sites.In summary,results of this thesis revealed that there was a rich diversity of cultivable bacteria in seawater around the Magellan Seamount;the bacterial community structures in seawater samples at the same depths of different sites of the Magellan Seamount area were significantly different,while there was little difference in archaeal bacterial community structures among these samples.Therefore,the Magellan Seamount exerted great influence on the bacterial biogeographical distribution around it.Studies in this thesis will enhance people's understanding of the microbial diversity,microbial community structures particularity and the driving mechanisms of this particularity in seamount ecosystem.