Deep sediments host many archaeal lineages, including those of the Asgard superphylum that may depend on/require syntrophic partnerships. Our knowledge about sedimentary archaeal diversity and their metabolic pathways and syntrophic partners is still very limited. We present here new genomes of Helarchaeota and co-occurring sulfate-reducing bacteria (SRB) recovered from organic-rich sediments off Costa Rica Margin. Our molecular analyses revealed three new metagenome-assembled genomes (MAGs) affiliating with Helarchaeota, each of which has three variants of the methyl-CoM reductase-like (MCR-like) complex that may enable them to oxidize short-chain alkanes anaerobically. These Helarchaeota have no multi-heme cytochromes (MHCs) but have Group 3b and Group 3c [NiFe] hydrogenases, and formate dehydrogenase, and therefore could transfer the reducing equivalents generated from alkane oxidation to external partners via the transfer of these substances. We also recovered five MAGs of SRB affiliated with the class of Desulfobacteria, two of which showed relative abundances (represented by genome coverages) positively correlated with those of the three Helarchaeota. Genome analysis suggested that these SRB bacteria have the capacity of H2 and formate utilizations and may facilitate electron transfers from other organisms by means of these reduced substances. Our findings suggest that Helarchaeota may metabolize synergistically with SRB in marine anoxic sediments, and exert an important influence on the carbon cycle by mitigating the hydrocarbon emission from sediments to the overlying ocean.

中文翻译：

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哥斯达黎加海缘海底沉积物中的Helarchaeota和减少硫酸盐的共生细菌

深沉的沉积物拥有许多古细菌世系，包括可能依赖/需要同养关系的Asgard superphylum的世系。我们对沉积古细菌多样性及其代谢途径和营养同伴的了解仍然非常有限。我们在这里介绍了Helarchaeota的新基因组，以及从哥斯达黎加边缘附近富含有机物的沉积物中回收的共生硫酸盐还原细菌（SRB）。我们的分子分析揭示了三个新的与Helarchaeota相关的元基因组组装基因组（MAGs），每个基因组具有甲基-CoM还原酶样（MCR-like）复合物的三个变体，可以使它们厌氧氧化短链烷烃。这些Helarchaeota没有多血红素细胞色素（MHC），但具有3b组和3c组[NiFe]氢化酶和甲酸脱氢酶，因此可以通过这些物质的转移将烷烃氧化生成的还原当量转移到外部伙伴。我们还回收了五种与脱硫细菌相关的SRB MAG，其中两个显示相对丰度（以基因组覆盖率表示）与三个Helarchaeota的丰度呈正相关。基因组分析表明，这些SRB细菌具有H2和甲酸利用的能力，并可能通过这些还原物质促进其他生物体的电子转移。我们的发现表明，Helarchaeota可以与海洋缺氧沉积物中的SRB协同代谢，并通过减轻从沉积物到上覆海洋的碳氢化合物排放，对碳循环产生重要影响。