To distinguish between the distribution and activity of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in the Pearl River estuary (PRE), we investigated the DNA- and cDNA-based -amoA and arch-amoA genes on three size-fractionated particles of >3.0 μm, 0.45‒3.0 μm, and 0.22‒0.45 μm. Results showed that AOB were more abundant in the freshwater with high concentrations of ammonium (NH4+) and low dissolved oxygen, whereas AOA were dominant in the NH4+-depleted seawater and sensitive to temperature. Obvious shifts in ammonia-oxidizing communities were found along the salinity gradient in the PRE. AOB clearly presented a particle-associated nature, as evidenced by higher relative abundance of amoA genes attached to the large particles (> 3.0 μm) and their transcripts exclusively detected on this fraction. Moreover, higher transcriptional activity (indicated by the cDNA/DNA ratio) of AOB on the large particles, suggesting AOB were actively involved in ammonia oxidation despite their lower abundance in the mid- and lower estuarine regions. In contrast, AOA exhibited higher transcriptional activity on the 0.45‒3.0 µm and 0.22‒0.45 μm particles, implying the free-living strategy of these microbes. Together, these findings from field observations provide useful information on the ecological strategies of ammonia-oxidizing communities in response to different environmental conditions.

中文翻译：

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珠江口粒径分级颗粒中氨氧化剂的分布及活性

为了区分珠江口（PRE）氨氧化细菌（AOB）和氨氧化古细菌（AOA）的分布和活性，我们研究了基于DNA和cDNA的-amoA和arch-amoA基因> 3.0 μm、0.45-3.0 μm 和 0.22-0.45 μm 的三种粒度分级颗粒。结果表明，AOB 在高浓度铵（NH4+）和低溶解氧的淡水中更为丰富，而 AOA 在缺乏 NH4+ 的海水中占主导地位，并且对温度敏感。沿 PRE 的盐度梯度发现氨氧化群落的明显变化。AOB 清楚地呈现出与颗粒相关的性质，如附着在大颗粒 (> 3.0 μm) 上的 amoA 基因的相对丰度较高以及仅在该部分检测到的转录本所证明。而且，AOB 在大颗粒上的较高转录活性（由 cDNA/DNA 比率表示），表明 AOB 积极参与氨氧化，尽管它们在河口中下游地区的丰度较低。相比之下，AOA 对 0.45-3.0 µm 和 0.22-0.45 µm 颗粒表现出更高的转录活性，暗示这些微生物的自由生存策略。总之，这些来自现场观察的发现为氨氧化群落响应不同环境条件的生态策略提供了有用的信息。45-3.0 µm 和 0.22-0.45 µm 颗粒，暗示这些微生物的自由生存策略。总之，这些来自现场观察的发现为氨氧化群落响应不同环境条件的生态策略提供了有用的信息。45-3.0 µm 和 0.22-0.45 µm 颗粒，暗示这些微生物的自由生存策略。总之，这些来自现场观察的发现为氨氧化群落响应不同环境条件的生态策略提供了有用的信息。