Department of Microbiology, IWWR, Radboud University, Heyendaalseweg 135, NL-6525 AJ, Nijmegen, The Netherlands.
Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands.
ISME J. 2021 Apr;15(4):1150-1164. doi: 10.1038/s41396-020-00840-7. Epub 2020 Dec 10.
Ammonia oxidation was considered impossible under highly acidic conditions, as the protonation of ammonia leads to decreased substrate availability and formation of toxic nitrogenous compounds. Recently, some studies described archaeal and bacterial ammonia oxidizers growing at pH as low as 4, while environmental studies observed nitrification at even lower pH values. In this work, we report on the discovery, cultivation, and physiological, genomic, and transcriptomic characterization of a novel gammaproteobacterial ammonia-oxidizing bacterium enriched via continuous bioreactor cultivation from an acidic air biofilter that was able to grow and oxidize ammonia at pH 2.5. This microorganism has a chemolithoautotrophic lifestyle, using ammonia as energy source. The observed growth rate on ammonia was 0.196 day, with a doubling time of 3.5 days. The strain also displayed ureolytic activity and cultivation with urea as ammonia source resulted in a growth rate of 0.104 day and a doubling time of 6.7 days. A high ammonia affinity (K = 147 ± 14 nM) and high tolerance to toxic nitric oxide could represent an adaptation to acidic environments. Electron microscopic analysis showed coccoid cell morphology with a large amount of intracytoplasmic membrane stacks, typical of gammaproteobacterial ammonia oxidizers. Furthermore, genome and transcriptome analysis showed the presence and expression of diagnostic genes for nitrifiers (amoCAB, hao, nor, ure, cbbLS), but no nirK was identified. Phylogenetic analysis revealed that this strain belonged to a novel bacterial genus, for which we propose the name "Candidatus Nitrosacidococcus tergens" sp. RJ19.
氨氧化被认为在高度酸性条件下是不可能的,因为氨的质子化会导致底物可用性降低,并形成有毒的含氮化合物。最近,一些研究描述了在 pH 值低至 4 的条件下生长的古菌和细菌氨氧化菌,而环境研究则观察到在更低的 pH 值下硝化作用的存在。在这项工作中,我们报告了一种新型γ变形菌氨氧化细菌的发现、培养以及生理、基因组和转录组特征,该细菌是通过连续生物反应器培养从酸性空气生物滤池中富集得到的,能够在 pH 2.5 下生长和氧化氨。这种微生物具有化能自养生活方式,以氨作为能源。在氨上观察到的生长速率为 0.196 天,倍增时间为 3.5 天。该菌株还表现出脲酶活性,用尿素作为氨源培养导致生长速率为 0.104 天,倍增时间为 6.7 天。高氨亲和力(K = 147 ± 14 nM)和对有毒的一氧化氮的高耐受性可能是对酸性环境的适应。电子显微镜分析显示球菌细胞形态,具有大量的胞内膜堆叠,这是γ变形菌氨氧化菌的典型特征。此外,基因组和转录组分析表明存在并表达了硝化菌(amoCAB、hao、nor、ure、cbbLS)的诊断基因,但没有鉴定出 nirK。系统发育分析表明,该菌株属于一个新的细菌属,我们建议将其命名为“Candidatus Nitrosacidococcus tergens”sp. RJ19。