Department of Biological Sciences, University of Alberta, CW 405 Biological Sciences Bldg., Edmonton, AB, Canada.
Appl Microbiol Biotechnol. 2021 Sep;105(18):7009-7021. doi: 10.1007/s00253-021-11529-y. Epub 2021 Aug 28.
Maintaining an optimal pH that simultaneously supports plants, fish, and nitrifying microorganisms is a challenge in recirculating aquaponics systems as nitrification is optimal at a slightly alkaline pH and plant growth is optimal at a slightly acidic pH. Freshwater fish tolerate pH > 5.5. Our aim was to adapt a microbial inoculum for a recirculating aquaponics system from an operational pH of 7.6 to 5.6, compare nitrification activity and production of NO, and describe changes in the adapted versus unadapted microbial communities. Four adaptation strategies were tested; our results indicated that a gradual reduction from pH 7.6 to 5.6, along with a gradual reduction followed by a gradual return of available ammonium, was the best strategy resulting in retention of 81% nitrification activity at pH 5.6 compared to pH 7.6. 16S rRNA gene amplicon sequencing and qPCR enumeration of nitrification-related genes showed that the composition of pH 5.6 adapted microbial communities from all four adaptation strategies was similar to one another and distinct from those operating at pH 7.6, with enrichment of comammox clade B bacteria over ammonia-oxidizing bacteria and thaumarchaeota. NO production of the pH 5.6 adapted microbial communities was below detection in all adaptation experiments, likely due to the increased proportion of comammox bacteria. Aquaponics biofilters enriched with comammox bacteria and adapted to function at pH 5.6 can be a desirable inoculum for freshwater recirculating aquaponics systems to retain nitrification activity and improve crop yields.Key points• Microbial communities adapted from pH 7.6 to pH 5.6 retained 81% nitrification activity.• Microbial communities adapted from pH 7.6 to pH 5.6 were enriched in comammox bacteria.• Comammox-enriched microbial communities did not produce N O.
在循环水养殖系统中，维持既能支持植物、鱼类又能支持硝化微生物的最佳 pH 值是一项挑战，因为硝化作用在略碱性 pH 值下最佳，而植物生长在略酸性 pH 值下最佳。淡水鱼能耐受 pH 值>5.5。我们的目的是将一种微生物接种物从 7.6 的运行 pH 值适应到 5.6，比较硝化活性和 NO 的产生，并描述适应和未适应的微生物群落的变化。测试了四种适应策略；结果表明，从 pH 值 7.6 逐渐降低到 5.6，同时随着可用铵的逐渐降低然后逐渐恢复，是最佳策略，与 pH 值 7.6 相比，在 pH 值 5.6 时保留了 81%的硝化活性。16S rRNA 基因扩增子测序和硝化相关基因的 qPCR 计数表明，来自所有四种适应策略的 pH 值 5.6 适应微生物群落的组成彼此相似，与在 pH 值 7.6 下运行的微生物群落不同，氨氧化细菌和古菌的 comammox 菌科 B 细菌富集。在所有适应实验中，pH 值 5.6 适应微生物群落的 NO 产生都低于检测限，这可能是由于 comammox 细菌的比例增加。富含有 comammox 细菌并适应在 pH 值 5.6 下运行的水培生物滤器可以成为淡水循环水养殖系统的理想接种物，以保持硝化活性并提高作物产量。关键点• 从 pH 值 7.6 适应到 pH 值 5.6 的微生物群落保留了 81%的硝化活性。• 从 pH 值 7.6 适应到 pH 值 5.6 的微生物群落富含 comammox 细菌。• 富含 comammox 的微生物群落不产生 N O。
