Ammonia-oxidising archaea and nitrite-oxidising bacteria are common members of marine sponge microbiomes. They derive energy for carbon fixation and growth from nitrification - the aerobic oxidation of ammonia to nitrite and further to nitrate - and are proposed to play essential roles in the carbon and nitrogen cycling of sponge holobionts. In this study, we characterise two novel nitrifying symbiont lineages, Candidatus Nitrosokoinonia and Candidatus Nitrosymbion in the marine sponge Coscinoderma matthewsi using a combination of molecular tools, in situ visualisation, and physiological rate measurements. Both represent a new genus in the ammonia-oxidising archaeal class Nitrososphaeria and the nitrite-oxidising bacterial order Nitrospirales, respectively. Furthermore, we show that larvae of this viviparous sponge are densely colonised by representatives of Ca. Nitrosokoinonia and Ca. Nitrosymbion indicating vertical transmission. In adults, the representatives of both symbiont genera are located extracellularly in the mesohyl. Comparative metagenome analyses and physiological data suggest that ammonia-oxidising archaeal symbionts of the genus Ca. Nitrosokoinonia strongly rely on endogenously produced nitrogenous compounds (i.e., ammonium, urea, nitriles/cyanides, and creatinine) rather than on exogenous ammonium sources taken up by the sponge. Additionally, the nitrite-oxidising bacterial symbionts of the genus Ca. Nitrosymbion may reciprocally support the ammonia-oxidisers with ammonia via the utilisation of sponge-derived urea and cyanate. Comparative analyses of published environmental 16S rRNA gene amplicon data revealed that Ca. Nitrosokoinonia and Ca. Nitrosymbion are widely distributed and predominantly associated with marine sponges and corals, suggesting a broad relevance of our findings.

中文翻译：

---

共存的硝化共生体谱系是垂直遗传的，并且广泛存在于海绵中

氨氧化古菌和亚硝酸盐氧化细菌是海洋海绵微生物组的常见成员。它们通过硝化（氨有氧氧化为亚硝酸盐并进一步氧化为硝酸盐）获得碳固定和生长的能量，并被认为在海绵全生物的碳和氮循环中发挥重要作用。在这项研究中，我们结合分子工具、原位可视化和生理速率测量，描述了海洋海绵 Coscinoderma matthewsi 中两种新型硝化共生体谱系：Candidatus Nitrosokoinonia 和 Candidatus Nitrosymbion。两者分别代表氨氧化古菌纲 Nitrososphaeria 和亚硝酸盐氧化细菌目 Nitrospirales 中的一个新属。此外，我们还发现这种胎生海绵的幼虫密集地栖息着 Ca 的代表。 Nitrosokoinonia 和 Ca. Nitrosymbion 指示垂直传播。在成人中，两个共生体属的代表都位于细胞外的中胚层。比较宏基因组分析和生理数据表明，Ca 属的氨氧化古菌共生体。亚硝化细菌强烈依赖于内源产生的含氮化合物（即铵、尿素、腈/氰化物和肌酸酐），而不是海绵吸收的外源铵源。此外，Ca 属的亚硝酸盐氧化细菌共生体。硝基共生体可以通过利用海绵衍生的尿素和氰酸盐，与氨相互支持氨氧化剂。对已发表的环境 16S rRNA 基因扩增子数据的比较分析表明，Ca. Nitrosokoinonia 和 Ca.硝化共生体分布广泛，主要与海绵和珊瑚有关，这表明我们的发现具有广泛的相关性。