Cultivation and genomic analysis of Candidatus Nitrosocaldus islandicus, a novel obligately thermophilic ammonia-oxidizing thaumarchaeon

Ammonia-oxidizing archaea (AOA) within the phylum Thaumarchaea are the only known aerobic ammonia oxidizers in geothermal environments. Although molecular data indicate the presence of phylogenetically diverse AOA from the Nitrosocaldus clade and the group 1.1a Thaumarchaea in terrestrial high-temperature habitats, only one enrichment culture of an AOA thriving above 50°C has been functionally characterized and published. From the biofilm of an Icelandic hot spring (73 °C), we have obtained a high (~85%) enrichment of a novel thaumarchaeon from the deep-branching Nitrosocaldaceae family and determined its complete genome sequence. This AOA, which we provisionally refer to as “Candidatus Nitrosocaldus islandicus”, is an obligately thermophilic chemolithoauto trophic ammonia oxidizer, which stoichiometrically converts ammonia to nitrite.

栖居于奇古菌门（Thaumarchaea）的氨氧化古菌（Ammonia-oxidizing archaea, AOA）是目前已知地热环境中唯一的好氧氨氧化微生物。尽管分子数据显示，陆地高温生境中存在隶属于亚硝化嗜热菌属分支（Nitrosocaldus clade）与1.1a类奇古菌（group 1.1a Thaumarchaea）的系统发育多样性丰富的AOA，但目前仅有一种在50℃以上环境中存活的AOA富集培养物得到了功能表征并正式发表。我们从冰岛一处73℃热泉的生物膜中，获得了一株隶属于深分支亚硝化嗜热菌科（Nitrosocaldaceae）的新型奇古菌的约85%富集培养物，并测定了其完整基因组序列。该AOA被我们暂命名为‘Candidatus Nitrosocaldus islandicus’，属于专性嗜热化能自养氨氧化菌，能够以化学计量比将氨转化为亚硝酸盐。