Microbial Diversity And Sulfur Oxidation Characteristics Of Hydrothermal Plume Of Carlsberg Ridge In Northwest Indian Ocean

The deep-sea hydrothermal region has been considered as a kind of extreme ecosystem with dark,high temperature,high pressure and abrupt physical and chemical gradients since its discovery.Abundant microbial groups inhabit in hydrothermal plume,in which sulfur oxidizing microorganisms,as the primary producers in the hydrothermal environment,mediate the energy flow by oxidizing various reduced sulfur compounds.In 2017,for the first time in the world,China carried out a manned deep diving survey of the Carlsberg ridge in the northwest Indian Ocean,and successfully discovered the hydrothermal region?Wocan,Daxi and Tianxiu?.Starting from the microbial diversity and metabolic function of Carlsberg ridge hydrothermal plume,this study focuses on Thiomacrorhabdus,a chemoautotrophic sulfur-oxidizing bacteria,conducts in-depth work on physiological and biochemical characteristics,the metabolic mechanism of sulfur oxidation and carbon fixation,and the characteristics of extracellular accumulation of elemental sulfur.Based on this,this paper is divided into the following three parts:Part 1: Bacterial and archaeal diversity of 17 deep-sea hydrothermal plume / sea water from Wocan 1,Wocan 2,Daxi and Tianxiu in the Carlsberg ridge of the northwest Indian Ocean were investigated by 16 S r RNA gene high-throughput sequencing method.The results showed that the bacterial groups in Carlsberg ridge sea water in the northwest Indian Ocean mainly include Gamaproteobacteria,Alphaproteobacteria,Deltaproteobacteria,SAR202,Actinobacteria,Acidobacteria,Bacteroidetes etc.And the abundance of SAR202 in the samples of Daxi and Tianxiu hydrothermal region was significantly higher than that in the samples of Wocan hydrothermal region.Compared with the seawater samples,sulfurimonas and sulfurovum in Epsilonbacteraeota are the dominant groups in plume,contents in different samples are 19.96-47.49% respectively and 9.92-11.95%.The dominant groups of archaea are mainly Thaumarchaeota and Euryarchaeota,which are concentrated in three groups of Marine_group₁,Methanobacteria and Thermoplasmata.Furthermore,the metabolic function of microorganisms in hydrothermal plume / seawater was analyzed by macrogenomic sequencing.The results show that the pattern of microbial carbon fixation in the hydrothermal plume of the Carlsberg ridge in the northwest Indian Ocean is varied,including r TCA,CBB,WL,DC/4HB,3HP/4HB and 3HP,among which r TCA,DC / 4HB,WL,CBB are the main carbon fixation pathway in Carlsberg ridge hydrothermal plume.In addition,relative to the surrounding seawater,the sulfur metabolism genes in the plume are rich and abundant,including thiosulfate oxidation,sulfide oxidation,dissimilated sulfate reduction,sulfur oxidation,assimilated sulfate reduction,anaerobic sulfate reduction,thiosulfate disproportionation and sulfite oxidation pathways.There are differences in sulfur metabolism in different hydrothermal regions,sulfur oxidation and sulfate assimilation are the most abundant in the plume of Wocan 1.Part 2: In this paper,a new strain,Thiomicrorhabdus sp.srain 13-15 A,isolated from the hydrothermal plume of the Carlsberg ridge in the northwest Indian Ocean was analyzed for its physiological and biochemical characteristics and genome annotation based on culturable method.The results showed that strain 13-15 A was an obligately chemolithoautotrophic,sulfur-oxidizing bacteria,and the optimum growth conditions were: micro oxygen consumption?2%?,temperature 28 oC,p H7.0 and 680 m M Na Cl;and capable of growth using thiosulfate,sulfide,elemental sulfur or tetrathionate as the sole energy source,carbon dioxide as the sole carbon source,and molecular oxygen as sole electron acceptor.Genome-wide analysis showed that the genome size of Thiomicrorhabdus sp.srain 13-15 A was about 3.08 Mbp,including a chromosome of 2.8Mbp and a plasmid of about 240 Kb.Its genome contains a complete set of sox multienzyme complex system?sox XA,sox YZ,sox B and sox CD?.In addition,there are Sqr?sulfur: quinone reduce?gene and Fcc?flavor to chrome-c sulfur dehydrogenase?gene.The genome contains all the enzymes that encode Calvin cycle.It has genes that encode carboxygenase,and it carries cbb3 type cytochrome oxidase,which can help it survive in low oxygen and low carbon dioxide environment.In addition,the plasmid encodes some heavy metal resistant genes,which shows its adaptation mechanism to extreme hydrothermal environment.Part 3: In this paper,the morphology of the excreted elemental sulfur of Thiomicrorhabdus was observed under different culture conditions.The results of SEM showed that the shape of elemental sulfur was mainly spherical,and there were some cluster,rhombus and irregular shapes,ranging from several nanometers to tens of microns;the shape of elemental sulfur had nothing to do with oxygen content and pressure.It suggests that the biosulfur morphology in the in situ environment of deep sea is similar to that observed in laboratory.A layer of film or screen like material is wrapped on the surface of the extracellular elemental sulfur,which contents C,O and N organic elements,among which the percentage of C element accounts for 70%-80%.The total sugar content of the coated film on the surface of sulfur particles was determined to be 61 mg / L by phenol sulfuric acid method.This is the first experiment to confirm that the surface of the extracellular sulfur granules contains polysaccharide.The results enrich the understanding of the microbial diversity of deep-sea hydrothermal plume and the energy metabolism mechanism of Thiomicrorhabdus,which provide a reference for studying the origin of life,understanding the structure of hydrothermal plume and evaluating the role of Thiomacrorhabdus in the cycle of carbon,nitrogen,sulfur and other elements in the hydrothermal environment.