Inefficient syntrophic propionate degradation causes severe operating disturbances and reduces biogas productivity in many high‐ammonia anaerobic digesters, but propionate‐degrading microorganisms in these systems remain unknown. Here, we identified candidate ammonia‐tolerant syntrophic propionate‐oxidising bacteria using propionate enrichment at high ammonia levels (0.7–0.8 g NH₃ L⁻¹) in continuously‐fed reactors. We reconstructed 30 high‐quality metagenome‐assembled genomes (MAGs) from the propionate‐fed reactors, which revealed two novel species from the families Peptococcaceae and Desulfobulbaceae as syntrophic propionate‐oxidising candidates. Both MAGs possess genomic potential for the propionate oxidation and electron transfer required for syntrophic energy conservation and, similar to ammonia‐tolerant acetate degrading syntrophs, both MAGs contain genes predicted to link to ammonia and pH tolerance. Based on relative abundance, a Peptococcaceae sp. appeared to be the main propionate degrader and has been given the provisional name “Candidatus Syntrophopropionicum ammoniitolerans”. This bacterium was also found in high‐ammonia biogas digesters, using quantitative PCR. Acetate was degraded by syntrophic acetate‐oxidising bacteria and the hydrogenotrophic methanogenic community consisted of Methanoculleus bourgensis and a yet to be characterised Methanoculleus sp. This work provides knowledge of cooperating syntrophic species in high‐ammonia systems and reveals that ammonia‐tolerant syntrophic propionate‐degrading populations share common features, but diverge genomically and taxonomically from known species.

中文翻译：

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在高氨水平下进行丙酸丙酸氧化的新型细菌的富集和描述

在许多高氨厌氧消化器中，低效的共养丙酸盐降解会导致严重的操作干扰并降低沼气生产率，但这些系统中的丙酸盐降解微生物仍然未知。在这里，我们使用高氨水平（0.7-0.8 g NH ₃ L ^-1) 在连续进料反应器中。我们从丙酸反应器中重建了 30 个高质量的宏基因组组装基因组 (MAG)，揭示了来自 Peptococccaceae 和 Desulfobulbaceae 科的两个新物种作为丙酸共养氧化候选物。两种 MAG 都具有共养能量守恒所需的丙酸氧化和电子转移的基因组潜力，并且与耐氨乙酸降解同养菌类似，两种 MAG 都包含预测与氨和 pH 耐受性相关的基因。基于相对丰度，Peptococcaceae sp。似乎是主要的丙酸盐降解剂，并已被赋予临时名称“ CandidatusSyntrophopropionicum ammoniitolerans”。使用定量 PCR 在高氨沼气消化器中也发现了这种细菌。乙酸盐被同养乙酸盐氧化细菌降解，氢营养产甲烷群落由Methanoculleus bourgensis和尚未表征的Methanoculleus sp. 组成。这项工作提供了高氨系统中合作共养物种的知识，并揭示了耐氨的共养丙酸盐降解种群具有共同特征，但在基因组和分类学上与已知物种不同。