The nutrient and oxygen gradient present in marine sediments promotes high levels of microbial diversity. We applied metagenomics and biogeochemical tools to analyze microbial communities in different sediment depths (0–4 m below sea floor, mbsf) from Guanabara Bay, Brazil, a brackish tropical ecosystem with a history of massive anthropogenic impacts, and a largely unknown sediment microbial diversity. Methanogens (e.g. Methanosarcinales, Methanomicrobiales) were more abundant at 1 mbsf, while sulphate-reducing microbes (Desulfurococcales, Thermoprotales, and Sulfolobales) were more abundant at deeper layers (4 mbsf; corresponding to 3 K Radiocarbon years before present, Holocene Epoch). Taxonomic analyzes and functional gene identification associated with anaerobic methane oxidation (e.g. monomethylamine methyltransferase (mtmB), trimethylamine methyltransferase (mttB) and CO dehydrogenase/acetyl-CoA synthase delta subunit) and sulfate reduction indicated the dominance of Campylobacteria (Sulfurimonas) at deeper sediment layers. Gene sequences related to assimilation of inorganic sulfur increased with depth, while organic sulfur related sequences decrease, accompanying the clear reduction in the concentration of sulfur, organic carbon and chla torwards deeper layers. Analyzes of metagenome assembled genomes also led to the discovery of a novel order within the phylum Acidobacteriota, named Guanabacteria. This novel order had several in silico phenotyping features that differentiate it from closely related phylogenetic neighbors (e.g. Acidobacteria, Aminicenantes, and Thermoanaerobaculum), including several genes (carbon monoxide dehydrogenase, CO dehydrogenase/CO-methylating acetyl-CoA synthase complex subunit beta, heterodisulfide reductase, sulfite exporter TauE/SafE family protein, sulfurtransferase) that relevant for the S and C cycles. Furthermore, the recovered Bathyarchaeota genome SS9 illustrates the methanogenic potential in deeper sediment layer.

海洋沉积物中存在的养分和氧气梯度促进了高水平的微生物多样性。我们使用宏基因组学和生物地球化学工具分析了巴西瓜纳巴拉湾不同咸水深度（海床下0–4 m，mbsf）的微生物群落，咸淡的热带生态系统具有巨大的人为影响历史，且很大程度上未知的泥沙微生物多样性。甲烷（例如Methanosarcinales，Methanomicrobiales）为在1个MBSF更加丰富，而硫酸盐还原微生物（Desulfurococcales，Thermoprotales和Sulfolobales）在更深的层（4 mbsf；对应于距今3 K的放射性碳年代，全新世）更丰富。与厌氧甲烷氧化有关的分类学分析和功能基因鉴定（例如单甲胺甲基转移酶（mtmB），三甲胺甲基转移酶（mttB）和CO脱氢酶/乙酰辅酶A合成酶δ亚基）和硫酸盐还原反应表明弯曲杆菌（Sulfurimonas）占优势）在更深的沉积层。与无机硫同化相关的基因序列随深度增加，而与有机硫相关的序列减少，伴随着硫，有机碳和透明质酸浓度的明显降低。对元基因组组装基因组的分析还导致发现了酸性细菌细菌门（Guanabacteria）中一个新的顺序。这个新的顺序有几个计算机上的表型特征，使其与密切相关的系统发育邻居（例如，酸性细菌，小型杆菌和热厌氧菌）区别开来。），包括与S和C循环相关的几种基因（一氧化碳脱氢酶，CO脱氢酶/ CO-甲基化乙酰辅酶A合酶亚基β，异二硫键还原酶，亚硫酸盐输出蛋白TauE / SafE家族蛋白，硫转移酶）。此外，回收的Bathyarchaeota基因组SS9说明了更深沉积层的产甲烷潜力。