Department of Microbiology, Miami University, 501 East High St, Oxford, OH, 45056, USA.
Department of Microbiology and Ecosystem Science, Division of Microbial Ecology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.
Microb Ecol. 2019 Nov;78(4):985-994. doi: 10.1007/s00248-019-01378-8. Epub 2019 Apr 11.
Ammonia-oxidizing bacteria (AOB) within the genus Nitrosomonas perform the first step in nitrification, ammonia oxidation, and are found in diverse aquatic and terrestrial environments. Nitrosomonas AOB were grouped into six defined clusters, which correlate with physiological characteristics that contribute to adaptations to a variety of abiotic environmental factors. A fundamental physiological trait differentiating Nitrosomonas AOB is the adaptation to either low (cluster 6a) or high (cluster 7) ammonium concentrations. Here, we present physiological growth studies and genome analysis of Nitrosomonas cluster 6a and 7 AOB. Cluster 6a AOB displayed maximum growth rates at ≤ 1 mM ammonium, while cluster 7 AOB had maximum growth rates at ≥ 5 mM ammonium. In addition, cluster 7 AOB were more tolerant of high initial ammonium and nitrite concentrations than cluster 6a AOB. Cluster 6a AOB were completely inhibited by an initial nitrite concentration of 5 mM. Genomic comparisons were used to link genomic traits to observed physiological adaptations. Cluster 7 AOB encode a suite of genes related to nitrogen oxide detoxification and multiple terminal oxidases, which are absent in cluster 6a AOB. Cluster 6a AOB possess two distinct forms of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and select species encode genes for hydrogen or urea utilization. Several, but not all, cluster 6a AOB can utilize urea as a source of ammonium. Hence, although Nitrosomonas cluster 6a and 7 AOB have the capacity to fulfill the same functional role in microbial communities, i.e., ammonia oxidation, differentiating species-specific and cluster-conserved adaptations is crucial in understanding how AOB community succession can affect overall ecosystem function.
亚硝化单胞菌属（Nitrosomonas）中的氨氧化细菌（AOB）能够完成硝化作用的第一步，即氨氧化，广泛存在于各种水生和陆地环境中。Nitrosomonas AOB 被分为六个定义明确的群，这些群与生理特征相关，有助于适应各种非生物环境因素。区分 Nitrosomonas AOB 的一个基本生理特征是对低（6a 群）或高（7 群）氨浓度的适应。在这里，我们介绍了 Nitrosomonas 6a 群和 7 群 AOB 的生理生长研究和基因组分析。6a 群 AOB 在 ≤1mM 铵时表现出最大生长速率，而 7 群 AOB 在 ≥5mM 铵时具有最大生长速率。此外，7 群 AOB 比 6a 群 AOB 更能耐受高初始铵和亚硝态氮浓度。6a 群 AOB 被初始 5mM 亚硝态氮完全抑制。基因组比较用于将基因组特征与观察到的生理适应联系起来。7 群 AOB 编码了一套与氮氧化物解毒和多种末端氧化酶相关的基因，而 6a 群 AOB 则没有这些基因。6a 群 AOB 拥有两种不同形式的核酮糖-1,5-二磷酸羧化酶/加氧酶（RuBisCO），并且一些（但不是全部）6a 群 AOB 可以利用尿素作为铵源。因此，尽管 Nitrosomonas 6a 群和 7 群 AOB 都有能力在微生物群落中发挥相同的功能，即氨氧化，但区分特定种和群保守的适应是理解 AOB 群落演替如何影响整体生态系统功能的关键。
