Metabolisms Of The Deep-sea Hydrothermal Archaea DPANN And Cold-seep Sulfur-oxidizing Bacteria And Their Roles In Driving Elemental Cycles

In various natural environments,microorganisms exhibit high biomass and diversity.They are considered to play a key driving role in global elemental cycles.Among them,the lifestyles of microorganisms with high abundance and special metabolic processes in deep-sea special habitats,such as cold springs and hydrothermal vents,and their contributions to element cycling have received extensive attention.In this study,based on metagenomics and molecular biology,the metabolisms of hydrothermal highly abundant archaea DPANN and the cold-seep sulfur-oxidizing bacteria were analyzed.Their pathways and mechanisms driving the key elemental cycle were also described.This study provides data support to understand the microbial metabolism and speculate their ecological functions.Archaea living in deep-sea hydrothermal ecosystem have attracted great scientific interest,due to their unique evolutionary status,biological functions,and ecological roles.In order to understand the community structure and metabolic functions of archaea in deep-sea hydrothermal vents,this study conducted metagenomic sequencing and analysis of hydrothermal sediments in the western Pacific.The results showed that DPANN group had the highest abundance among archaea,and they generally had smaller genomes and incomplete key metabolic pathways,which could be complemented for by other means.In addition,hydrothermal DPANN archaea had the potential to assimilate nitrogen and metabolize sulfur-containing compounds,which may further drive the sulfur and nitrogen elemental cycles.Considering their high abundance in hydrothermal ecosystems,DPANN was proposed to have potential ecological significance in the deep-sea hydrothermal vents.When understanding the microbial metabolism in deep-sea cold seep and hydrothermal vents,non-culture methods provided much data about that.However,in order to conduct further research on microbial mechanisms and comprehensively interpret the relationship between deep-sea microbial metabolism and the elemental cycles,it is necessary to conduct relevant research based on pure-cultured strains from a genetic perspective.In previous work,a typical sulfur-oxidizing bacterium,Erythrobacter flavus 21-3,was obtained from a deep-sea cold seep.Its novel sulfur oxidation pathway that converts sodium thiosulfate to zero-valent sulfur(ZVS)was revealed using genetic and molecular methods.However,it is still unclear whether this pathway works in situ,as well as in the deep-sea cold seep.Therefore,in this study,the wild-type strain of E.flavus 21-3 and knockout strains were cultivated in deep-sea cold seeps.The results showed that E.flavus 21-3 was able to produce ZVS through this pathway in the in-situ environment.Moreover,since E.flavus 21-3 could use the produced elemental sulfur as an energy source,this sulfuroxidizing pathway was proposed to be beneficial to the survival of this strain in cold seep environments.Furthermore,this pathway was widely present in the microorganisms living in the surface sediments,which presented the most active sulfur metabolism.It might contribute significantly to the sulfur cycling in cold seeps.This study confirmed the occurrence of this novel sulfur oxidation pathway in the in-situ environment and further elucidated the sulfur metabolism of E.flavus 21-3 in the deepsea cold seep environment,providing valuable reference for conducting in-situ experiments on deep-sea microbes.In the further study,E.flavus 21-3 was found to significantly increase its ZVS production under blue light stimulation.Through various methods,a novel pathway for blue light-promoted ZVS formation by a deep-sea sulfur-oxidizing bacterium was revealed: Following blue light stimulation,the histidine kinase LOV-1477 activates its cognate response regulator,DGC-2902.The DGC-2902 then releases c-di-GMP as an output response.Then,m Pil Z-1753 binds to c-di-GMP and activates Tsd A through interaction,resulting in more thiosulfates being converted to tetrathionates.The tetrathionates are then hydrolyzed by Sox B-277 and Sox B-285,then a large amount of ZVS was formed finally.This work reveals the relationship between the light sensing and the sulfur oxidation pathway in deep-sea cold-seep sulfur-oxidizing bacteria,which received little attention before.It also brings a new perspective for further study on sulfur metabolism and light utilization of cold-seep sulfur-oxidizing bacteria.In addition,this study also investigated the chemolithoautotrophic sulfuroxidizing bacterium Guyparkeria hydrothermalis SP2,isolated from deep-sea cold seep sediments.It was found that the strain SP2 could use the Sox system(sulfur-oxidizing enzyme system)to oxidize thiosulfate into ZVS,and fix carbon dioxide via the CalvinBenson-Bassham cycle.The electrons obtained from the former process could be used to generate energy for the latter process via the respiratory chain.The in-situ cultivation revealed that G.hydrothermalis SP2 could use reduced sulfur compounds,mainly sulfides,for its growth in deep-sea cold seeps.The major protein mediating this process was Fcc B(flavocytochrome c-sulfide dehydrogenase large subunit).During this process,large amounts of ZVS were produced efficiently,and Fcc B in the G.hydrothermalis SP2 was likely a highly efficient sulfide oxidase.This part of the study provides research materials and ideas to understand the ZVS formation and the sulfur cycle driven by chemolithoautotrophic sulfur-oxidizing bacteria in cold seeps.In summary,we combined various strategies to study important microbial communities from the cold seep and hydrothermal vents in the deep sea.Through nonculture technology,we speculated the metabolism of DPANN archaea,which were widespread in the deep-sea hydrothermal system.Next,we investigated the lifestyle of sulfur-oxidizing bacteria in cold seep through in-situ cultivation.Finally,a ZVS production coupling light response pathway of deep-sea sulfur-oxidizing bacteria was revealed,which received little attention before.These results contribute to understanding the biological processes in deep-sea special habitats and their roles in elemental cycles.