Microbial Diversity Of Submarine Rare Earth-rich Sediments And Ferromanganese Nodules In Western Pacific

Rare earth elements-rich sediments and ferromanganese nodules are strategic mineral resource in respect of their high research value and mining prospects.However,their microbial composition and community structure,as well as ecological roles remain large unknown.In this study,3 surface sediments,7 ferromanganese nodules,and 3 sediment cores(up to ～800 cm below the seafloor)samples were collected from the Western Pacific Ocean during its 67 th cruise.The contents of common and trace metal elements and rare earth elements were measured and analyzed using inductively coupled plasma mass spectrometry(ICP-MS).The high-throughput sequencing of 16 S r RNA genes V3-V4 region was also conducted to evaluate community diversity,in addition to their relationships with physical and chemical variables.The result demonstrated that a major of common metal elements and all rare earth elements showed higher level in ferromanganese nodules than in surface sediments.However,the cadmium(Cr)and scandium(Sc)displayed the converse trend.The abundant bacteria and archaea of surface sediments and ferromanganese nodules were Gammaproteobacteria,Alphaproteobacteria,followed by Crenarchaeota,Chloroflexi,Actinobacteriota,Bacteroidota,Firmicutes,and Acidobacteriota.However,the microbial composition displayed a significant difference between iron ferromanganese nodules and surface sediments(P<0.05).Higher level of ammonia oxidizing archaea,Crenarchaeota,potential Mn(II)oxidizing bacteria Shewanella and Colwellia,and iron reducing bacteria Magnetospiraceae occurred in ferromanganese nodules.Among them,Crenarchaeota is capable of providing energy within nodule environment via ammonia oxidation coupled with carbon fixation that is likely closed linked to Mn oxidation process.The prevalent bacteria and archaea in sediment cores(a total of 115 samples)included: Gammaproteobacteria(49.8%),Alphaproteobacteria(4.9%),Actinobacteriota(15.5%),Bacteroidota(11.9%),Firmicutes(4.2%),Chloroflexi(3.6%),Crenarchaeota(3.0%),and Acidobacteriota(2.0%)。The relative abundance of SAR324 clade,SAR202 clade,and Nitrosopumilaceae members declined with the depth,suggesting active ammonia oxidation and S transformation process at upper sediments.While heterotrophic Pedobacter,Pseudomonas,Fusobacterium,and Streptococcus occurred at deep sediments.Additionally,Pseudomonas(Gammaproteobacteria),Rhodococus(Actinobacteriota)occupied high level at sediment cores,and might be involved in rare earth element accumulation.This study provided insight into the key element cycling processes in rare earth rich-sediments and iron manganese nodules in deep-sea;and the formation of ferromanganese nodules as well as the enrichment and transformation of rare earth elements mediated with microbe.