Abstract In recirculating aquaculture systems (RAS), the crucial step of eliminating toxic N compounds like ammonia and nitrite is mediated via nitrifying microorganisms and takes place in biofilters. In this study, analyses of microorganisms colonizing biocarriers of nine moving-bed biofilters of three different RAS operated with freshwater, brackish or marine process water uncovered site specific communities. Illumina-based amplicon sequencing of the V4-region of the 16S rRNA gene revealed a high microbial diversity with 1000–2500 species-level operational taxonomic units (OTUs) in all biofilters with the highest diversity in the brackish RAS. Proteobacteria, Bacteriodetes, Plantomycetes, Chloroflexi and Nitrospirae represented the most abundant phyla. 76 out of 674 known genera occurred in all nine biofilters and were defined as core-taxa, including nitrifying bacteria (Nitrosomonas and Nitrospira) as well as members of the (heterotrophic) genera Planctomyces, Blastopirellula, Nannocystis and Lewinella. Nitrifying communities composed of different, closely related and so far uncultured members of Nitrosomonas and Nitrospira were identified, strongly indicating that several potentially novel ammonia and nitrite oxidizing species are present in RAS biofilters. Relatives of known comammox Nitrospira were detected in the brackish biofilters, revealing 94–99 % identity of the 16S rRNA gene sequence to Ns. inopinata. Salinity tolerance tests with biocarriers derived from biofilters of the three distinct RAS showed an unexpected broad physiological flexibility with regard to salinity. Nitrification performance of freshwater nitrifiers was drastically reduced with increasing salinity and nearly completely inhibited at 15 PSU, while the brackish and marine nitrifiers showed a high resistance and maintained nitrification activity in a broad range of salt concentrations. This data can help to improve the nitrification process in RAS with changing salinity of the process water.

中文翻译：

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淡水、咸水和海洋 RAS 生物过滤器中硝化生物膜的分类和功能分析

摘要 在循环水产养殖系统 (RAS) 中，消除氨和亚硝酸盐等有毒 N 化合物的关键步骤是通过硝化微生物介导的，并发生在生物过滤器中。在这项研究中，对三种不同 RAS 的九个移动床生物过滤器的生物载体的微生物定植进行了分析，这些过滤器使用淡水、微咸水或海洋工艺水运行，揭示了特定地点的群落。基于 Illumina 的 16S rRNA 基因 V4 区域的扩增子测序显示，在所有生物过滤器中具有 1000-2500 个物种级操作分类单位 (OTU)，在微咸 RAS 中具有最高的多样性。Proteobacteria、Bacteriodetes、Planttomycetes、Chloroflexi 和 Nitrospirae 代表了最丰富的门。674 个已知属中有 76 个出现在所有九个生物过滤器中，并被定义为核心分类群，包括硝化细菌（Nitrosomonas 和 Nitrospira）以及（异养的）Planctomyces, Blastopirellula, Nannocystis 和 Lewinella 属的成员。确定了由不同的、密切相关的且迄今为止未培养的亚硝化单胞菌和亚硝化螺旋体成员组成的硝化群落，强烈表明 RAS 生物过滤器中存在几种潜在的新型氨和亚硝酸盐氧化物种。在微咸生物过滤器中检测到已知 comammox Nitrospira 的亲属，揭示了 16S rRNA 基因序列与 Ns 的 94-99% 同一性。无花果。用源自三种不同 RAS 的生物过滤器的生物载体进行的耐盐性测试显示出关于盐度的出乎意料的广泛生理灵活性。淡水硝化菌的硝化性能随着盐度的增加而急剧降低，并且在 15 PSU 时几乎完全被抑制，而咸水和海洋硝化菌显示出高抵抗力并在很宽的盐浓度范围内保持硝化活性。该数据有助于改进 RAS 中的硝化过程，同时改变工艺水的盐度。