| A large number and a wide variety of microorganisms are distributed in the deepsea environment.Deep-sea microorganisms participate in the marine biogeochemical cycle directly or indirectly.These microorganisms also adopt complex physiological and biochemical characteristics and molecular mechanisms to adapt to extreme environments such as low temperature(local high temperature),high pressure,high salt,darkness,and oligotrophic conditions.Therefore,the study of deep-sea environmental microbes provides a theoretical basis for exploring marine biogeochemical cycles,revealing the adaptation mechanism and life evolution of microbes in extreme deep-sea environments.Located on the east of the Yap Ridge and the Yap Islands,the Yap Trench is 650 km long from north to south,with a depth of up to 8,527 m.To the north,it is connected with the world's deepest trench,the Mariana Trench,which is a typical ultra-abyssal environment.The extreme environmental characteristics of the Yap Trench restrict the distribution of biogenic elements such as carbon,nitrogen,and sulfur and the composition of biological communities,forming a unique material circulation and energy flow system in the ultra-abyssal environment.On June 13 th,2017,the manned submersible "Jiaolong" obtained sediments and benthic organisms such as sea cucumber,starfish and gammaridae at Yap Trench during 152-dive,38-voyage expedition.In this study,traditional cultural methods and highthroughput sequencing technology(V3-V4 variable region gene sequencing of 16 S r DNA and metagenomic sequencing)were adopted to study the microbial diversity of culturable microorganisms in the Yap Trench and Mariana Trench sediments,as well as the intestinal microbes of sea cucumber,starfish and gammaridae in the Yap Trench.Futher analysis were conducted to explore the diversity of microbes and their key enzyme genes of carbon,nitrogen,sulfur and other metabolic pathways in the intestinal environment of sea cucumber of Yap Trench,and to analyze the phylogenetic status of these genes.This study provides a theoretical reference for revealing the characteristics of the geochemical cycle of the deep sea environment and the evolution of life.1.586 strains of bacteria were isolated and cultured from deep-sea sediment samples from 11 stations in the Yap Trench and Mariana Trench.They belonged to Proteobacteria,Actinobacteria,Bacteroidetes and Firmicutes respectively.Among them,Proteobacteria were the predominated phylum,mainly including Alphaproteobacteria and Gammaproteobacteria.86 strains of fungi were isolated,belonging to Ascomycetes and Basidiomycetes.A total of 110 strains of bacteria were isolated from the intestines of sea cucumber,starfish and gammaridea,belonging to Proteobacteria,Firmicutes and Actinobacteria respectively.Alphaproteobacteria and Gammaproteobacteria dominated the intestinal microbes.2.The intestinal microbial diversity was analyzed by Miseq high-throughput sequencing of V3-V4 variable region of 16 S r DNA compared with that of offshore aquacultured sea cucumbers Apostichopus japonicus.The results showed that Yap Trench sea cucumber shared a high similarity with Synallactidae from deep sea.The intestinal microbial diversity(Simpson index and Chao1 index)and richness(ACE index and Shannon index)of the Yap Trench sea cucumber were lower than those of aquacultured sea cucumbers.The dominant bacteria of the Yap Trench sea cucumber included Gammaproteobacteria(34.1%),Alphaproteobacteria(16.0%),and Bacteroidetes(24.0%).The dominant archaea were Thaumarchaeota(98.8%).In the Yap Trench sea cucumber intestines,the relative abundance of chemoautotrophic ammonia-oxidizing archaea Nitrosopumilus were up to 95.6%,and nitrate-reducing bacterium Methylotenerawas 10.6%.Whereas,sulfatereducing bacteria(28.1%)and Sulfurovum(13.7%)harboured higher relative abundance in the intestine of aquacultured sea cucumbers.The distinct microbial composition might reflect the difference of nitrogen and sulfur cycle in abyssal and offshore sedimentary environments.Morevoer,the phylogenetic analysis based on the 16 S r DNA gene sequence indicated that Nitrosopumilus were closely related to Thaumarchaeota from the hadal sediments,and supported the theory that ammonia-oxidizing archaea(AOA)originated from land and expanded to the photic and dark oceans.3.Metagenomic sequencing was used to analyze the intestinal microbial composition and function of Yap Trench sea cucumber and cultured sea cucumbers.From the perspective of microbial structure,the intestinal bacteria of the sea cucumber of Yap Trench are dominated by Proteobacteria(64.3%),Gammaproteobacteria(39.6%)occupiedhighest abundance,followed by Bacteroidetes(17.7%)and Thaumarchaeota(9.1%).From the perspective of microbial function,comparison resultsbased on KEGG and COG database of Yap Trench sea cucumber showed that genes related to metabolic function(amino acid metabolism,carbohydrate metabolism,energy metabolism,etc.)were the predominated the functions,and the proportion of genes related to signal transduction and information processing function was also relatively high.The results of based on CAZy database showed that the relative abundance of glycoside transferases was the highest,followed by glycoside hydrolases and glycocarbohydrate lipases.It indicated that microorganisms in the deep sea had potential to transport and utilize extracellular amino acids,carbohydrate and other organic substances for heterotrophic metabolism.At the same time,the signal transduction and information processing genes were abundant,which might be the mechanism of intestinal microbes responsed to the extreme deep-sea environment(low temperature,extreme p H,high pressure and high salinity,etc.).4.Vast numbers of functional genes related to nitrogen metabolism pathways have been found in the intestinal metagenome of sea cucumber from Yap Trench,including genes involved in nitrogen fixation,denitrification,and nitrification pathways,such as ure C/D/H(encoding urease),nir B/K/D(encoding nitrite reductase),nor Q(encoding nitric oxide reductase),and amo A/B/C(encoding ammonia monooxygenase).The representative sequences of these genes encode proteins which are closely related to the protein sequences frommarine Nitrosopumilus of Thaumarchaeota.The results showed that the nitrogen fixation,nitrification and denitrification mediated by Nitrosopumilus were most important parts of the nitrogen cycle in the gut of sea cucumber from Yap Trench.The mcr A gene and pmo A gene involved in methane oxidation were found in the intestinal tract of Yap Trench sea cucumber in the genera of Nitrosopumilus,Nitrosospira and Nitrosomonas,indicating that methane production and oxidation are important components of the deep-sea carbon cycle.Abundant functional genes related to sulfur cycle had been found in the intestines of cultured sea cucumber,mainly including sqr(encoding sulfide: quinone reductase),apr A/B/E/X(encoding adenosylsulfate reductase),sat(encoding adenosylsulfate transferase),Sox A/B/X/Y/Z(encoding thiosulfate oxidation system)and dsr(encoding sulfite reductase).The sulfur oxidation and sulfate reduction processes of bacteria such as Halioglobus and Desulfobulbus are important components of the sulfur cycle in the offshore cultured area,which also reflects the sulfur cycle process in the near-shore nutrient-rich sediments. |
PDF Full Text Request