Environmental fluctuations in the availability of nutrients lead to intricate metabolic strategies. “Candidatus Accumulibacter phosphatis,” a polyphosphate-accumulating organism (PAO) responsible for enhanced biological phosphorus removal (EBPR) from wastewater treatment systems, is prevalent in aerobic/anaerobic environments. While the overall metabolic traits of these bacteria are well described, the nonavailability of isolates has led to controversial conclusions on the metabolic pathways used. In this study, we experimentally determined the redox cofactor preferences of different oxidoreductases in the central carbon metabolism of a highly enriched “Ca. Accumulibacter phosphatis” culture. Remarkably, we observed that the acetoacetyl coenzyme A reductase engaged in polyhydroxyalkanoate (PHA) synthesis is NADH preferring instead of showing the generally assumed NADPH dependency. This allows rethinking of the ecological role of PHA accumulation as a fermentation product under anaerobic conditions and not just a stress response. Based on previously published metaomics data and the results of enzymatic assays, a reduced central carbon metabolic network was constructed and used for simulating different metabolic operating modes. In particular, scenarios with different acetate-to-glycogen consumption ratios were simulated, which demonstrated optima using different combinations of glycolysis, glyoxylate shunt, or branches of the tricarboxylic acid (TCA) cycle. Thus, optimal metabolic flux strategies will depend on the environment (acetate uptake) and on intracellular storage compound availability (polyphosphate/glycogen). This NADH-related metabolic flexibility is enabled by the NADH-driven PHA synthesis. It allows for maintaining metabolic activity under various environmental substrate conditions, with high carbon conservation and lower energetic costs than for NADPH-dependent PHA synthesis. Such (flexible) metabolic redox coupling can explain the competitiveness of PAOs under oxygen-fluctuating environments.

中文翻译：

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通过氧化还原辅助因子分析和代谢网络建模揭示“磷脂酸杆菌”的代谢灵活性。

营养物质可用性的环境波动会导致复杂的代谢策略。“暂定Accumulibacter phosphatis，”一个储存多磷酸盐的生物体（PAO）负责强化生物除磷（EBPR）从废水处理系统，是普遍存在于需氧/厌氧环境。尽管这些细菌的总体代谢特征得到了很好的描述，但分离株的缺乏性却导致了有关所用代谢途径的有争议的结论。在这项研究中，我们通过实验确定了高浓度“ Ca ”的中央碳代谢中不同氧化还原酶的氧化还原辅因子偏好。。磷脂质积累菌。值得注意的是，我们观察到参与聚羟基链烷酸酯（PHA）合成的乙酰乙酰辅酶A还原酶是NADH偏好的，而不是表现出通常假定的NADPH依赖性。这可以重新考虑PHA积累作为厌氧条件下的发酵产物的生态作用，而不仅仅是压力响应。基于先前发布的代谢组学数据和酶促测定的结果，构建了减少的中心碳代谢网络，并将其用于模拟不同的代谢操作模式。尤其是，模拟了具有不同的乙酸盐/糖原消耗比的方案，这些方案证明了使用糖酵解，乙醛酸分流或三羧酸（TCA）循环分支的不同组合的最佳方案。从而，最佳的代谢通量策略将取决于环境（乙酸吸收）和细胞内存储化合物的可用性（聚磷酸盐/糖原）。NADH相关的代谢灵活性是由NADH驱动的PHA合成实现的。与依赖NADPH的PHA合成相比，它可在各种环境底物条件下维持代谢活性，并具有较高的碳守恒性和较低的能量成本。这种（灵活的）代谢氧化还原偶联可以解释PAO在氧气波动环境下的竞争力。与依赖NADPH的PHA合成相比，具有较高的碳保存量和较低的能源成本。这种（灵活的）代谢氧化还原偶联可以解释PAO在氧气波动环境下的竞争力。与依赖NADPH的PHA合成相比，具有较高的碳保存量和较低的能源成本。这种（灵活的）代谢氧化还原偶联可以解释PAO在氧气波动环境下的竞争力。