Ammonia tolerance is a universal characteristic among the ammonia-oxidizing bacteria (AOB); in contrast, the known species of ammonia-oxidizing archaea (AOA) have been regarded as ammonia sensitive, until the identification of the genus “Candidatus Nitrosocosmicus.” However, the mechanism of its ammonia tolerance has not been reported. In this study, the AOA species “Candidatus Nitrosocosmicus agrestis,” obtained from agricultural soil, was determined to be able to tolerate high concentrations of NH₃ (>1,500 μM). In the genome of this strain, which was recovered from metagenomic data, a full set of genes for the pathways of polysaccharide metabolism, urea hydrolysis, arginine synthesis, and polyamine synthesis was identified. Among them, the genes encoding cytoplasmic carbonic anhydrase (CA) and a potential polyamine transporter (drug/metabolite exporter [DME]) were found to be unique to the genus “Ca. Nitrosocosmicus.” When “Ca. Nitrosocosmicus agrestis” was grown with high levels of ammonia, the genes that participate in CO₂/HCO₃⁻ conversion, glutamate/glutamine syntheses, arginine synthesis, polyamine synthesis, and polyamine excretion were significantly upregulated, and the polyamines, including putrescine and spermidine, had significant levels of production. Based on genome analysis, gene expression quantification, and polyamine determination, we propose that the production and excretion of polyamines is probably one of the reasons for the ammonia tolerance of “Ca. Nitrosocosmicus agrestis,” and even of the genus “Ca. Nitrosocosmicus.”

中文翻译：

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耐高氨多胺的产生和排泄，以土壤氨氧化古生菌“Candidatus Nitrosocosmicus agrestis”为例

氨氧化细菌 (AOB) 的普遍特性是氨耐受性；相比之下，已知的氨氧化古菌 (AOA) 物种一直被认为对氨敏感，直到鉴定出“ Candidatus Nitrosocosmicus”属。然而，其氨耐受机制尚未见报道。在这项研究中，从农业土壤中获得的 AOA 物种“ Candidatus Nitrosocosmicus agrestis”被确定能够耐受高浓度的 NH ₃(>1,500 μM)。在从宏基因组数据中恢复的该菌株的基因组中，鉴定了多糖代谢、尿素水解、精氨酸合成和多胺合成途径的全套基因。其中，发现编码细胞质碳酸酐酶（CA）和潜在多胺转运蛋白（药物/代谢物输出蛋白[DME]）的基因是“ Ca ”属独有的。Nitrosocosmicus。” 当“ Ca. Nitrosocosmicus agrestis”在高水平氨下生长，氨是参与 CO ₂ /HCO ₃的基因^-转化、谷氨酸/谷氨酰胺合成、精氨酸合成、多胺合成和多胺排泄显着上调，多胺（包括腐胺和亚精胺）的产量显着增加。基于基因组分析、基因表达定量和多胺测定，我们提出多胺的产生和排泄可能是“ Ca ”耐氨的原因之一。Nitrosocosmicus agrestis”，甚至是“ Ca ”属。Nitrosocosmicus。”