The Hydrogen-and Sulfur-Oxidation Metabolism Of Thermophilic Chemolithoautotroph Hydrogenimonas Thermophila SWIR-17 Isolated From Deep-Sea Hydrothermal Vent

The deep-sea hydrothermal vents has become one of the most extreme environments on the earth due to darkness,oligotrophic,high pressure,and steep gradients and chemical gradients.It is a typical chemical autotrophic ecosystem.Chemoautotrophic microorganisms are the primary producers of the ecosystems,mainly through the oxidation of H₂ or reducing sulfides to obtain energy to fix CO₂,which supports the entire hydrothermal ecosystem and participate in the material circulation and energy metabolism in the hydrothermal system.However,due to the lack of cultivable strains,the current understanding of the metabolic mechanism and ecological functions of such microorganisms is still unknown.This study is based on a cultivable method to isolate and purify the chemoautotrophic bacteria from samples collected from Longqi hydrothermal vent in the Southwest Indian Ocean Ridge(SWIR)during the TS10.10 strains of key autotrophic bacteria have been isolated,mainly belonging to genus Sulfurimonas,Hydrogenimonas and Sulfurospirillum in?-Proteobacteria.Through sequence comparison,they have the highest homology of 92%-99%with other strains from hydrothermal vents.Among them,strain SWIR-13,SWIR-16 and SWIR-19 have the highest sequence homology with the Sulfurimonas paralvinellae GO25^T 16S r RNA,which are 97.17%,96.82%and 96.82%respectively.It is speculated that they might be potential new species;SWIR-15 has the highest homology with the genus Sulfurospirillum,only 92.92%,and it is indicated that it may be a potential new genus;in this study,we characterized the physiology and metabolic mechanisms of H.thermophila SWIR-17.Physiological characterizations show that H.thermophila SWIR-17 is a strict chemoautotrophic microorganism that can utilize molecular hydrogen,thiosulfate and sulfide as energy sources.None of the tested organic carbons could be used as energy source or carbon source.Growth was observed between 10-60?.Microaerobic,the oxygen concentration required for growth is no more than 2%;Molecular oxygen,nitrate,thiosulfate,elemental sulfur,sulfate and manganese dioxide could served as electron acceptors to support the growth when H₂ is used as an electron donor.It was discovered that this genus can be coupled with sulfate reduction and manganese reduction with hydrogen-oxidation firstly.This study found that this genus can use sulfur compounds as energy sources firstly.During the oxidation of thiosulfate,the extracellular sulfur was generated.In this study,the chemical composition,surface element composition and valence state,the surface organic matter,the crystal structures,and the morphology of the extracellular sulfur were studied in detail by means of X-ray diffraction technology,spectrometer measurement and scanning electron microscopy analysis.The results show that the extracellular accumulation is elemental sulfur,the spatial structure is basically the same as that of?-S8,and its surface contains C,N,O,S,etc.There are two valence states of sulfur,which are presumed to be S⁰ and SO₄^2-,respectively.The content of the two is basically the same,the surface is not coated by organic film,and the morphology and structure are regular,mainly spherical and rod-shaped.The diameter of the spherical sulfur particles is in the range of8-20?m;the length of the rod is in the range of 20?m-100?m.Genomic analysis resulted that the complete genome of H.thermophila SWIR-17 is about2.53M bp with G+C content of 33.6%.Gene annotation indicated that 2530 genes were predicted.There are many types of genes related to sulfur metabolism in this genome were annotated based on RAST.Among them,the genes involved in the sulfur oxidation pathway include the incomplete Sox multienzyme complex system(Sox XA,Sox YZ,Sox B,lacking of Sox CD),with the genes encode the pathway of sulfide oxidation but not the sulfur oxidation.There are a broad array of genes encoding[Ni Fe]-hydrogenase in the genome,including Group?,?,and?.Among them,there are 5 Group?hydrogenases,and 1 Group?and?,respectively,transcriptome analysis showed that Group I hydrogenase might play an important role in hydrogen oxidation.In addition,the genome contains two sets enzymes that encoded sulfate reduction pathway genes and sulfur reduction.This strain fixes CO₂ through the reductive tricarboxylic acid cycle(r TCA).Its nitrogen metabolism pathways include dissimilation nitrate reduction pathway,assimilation nitrate reduction pathway and denitrification pathway.The results of this study enriched the understanding of the hydrogen/sulfur oxidization mechanism of the chemoautotrophic microorganisms in hydrothermal vents,and provided more understanding of the characteristics of Hydrogenimonas,which provided an important reference for further evaluation of its role and ecological significance in the hydrothermal environment.