Abstract Fermentation at low pH is an efficient way to improve the competitiveness of biological succinic acid-producing process. Actinobacillus succinogenes shows good performance of succinic acid production under anaerobic conditions, but its succinic acid production capability at the low-pH is inefficient due to the poor acid resistance. Herein, a mutant A. succinogenes BC-4 with improved cell growth and succinic acid production under weak acid conditions was obtained by adaptive evolution. The specific growth rate and succinic acid production of BC-4 reached 0.13 g/L/h and 20.77 g/L, which were increased by 3.25- and 2.95- fold, respectively compared with the parent strain under anaerobic condition at pH 5.8. The activities of specific enzymes with ATP generation were significantly enhanced under weak acidic conditions, resulting in 1.28-fold increase in the maximum ATP level. Membrane fatty acid composition analysis demonstrated that the ratio of saturated to unsaturated fatty acids was decreased from 1.62 to 1.44 in mutant BC-4, leading to improved intracellular pH homeostasis. Furthermore, the change from long-chain to median-chain fatty acid might lower the permeability of H+ into cytoplasm for survival under acid stress. These results indicated that A. succinogenes BC-4 is a promising candidate for succinic acid production under weak acid condition.

中文翻译：

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适应性进化提高了琥珀酸放线杆菌的酸耐受性和琥珀酸产量

摘要 低pH发酵是提高生物琥珀酸生产工艺竞争力的有效途径。产琥珀酸放线杆菌在厌氧条件下表现出良好的琥珀酸生产性能，但其在低pH下的琥珀酸生产能力由于耐酸性差而效率低下。在此，通过适应性进化获得了在弱酸条件下具有改善的细胞生长和琥珀酸生产的突变体 A. succinogenes BC-4。BC-4 的比生长速率和琥珀酸产量分别达到 0.13 g/L/h 和 20.77 g/L，与在 pH 5.8 厌氧条件下的亲本菌株相比分别增加了 3.25 倍和 2.95 倍。在弱酸性条件下，产生 ATP 的特定酶的活性显着增强，导致 1. 最大 ATP 水平增加 28 倍。膜脂肪酸组成分析表明，突变体 BC-4 中饱和脂肪酸与不饱和脂肪酸的比例从 1.62 降低到 1.44，导致细胞内 pH 稳态的改善。此外，从长链脂肪酸到中链脂肪酸的变化可能会降低 H+ 进入细胞质的渗透性，以便在酸胁迫下生存。这些结果表明 A. succinogenes BC-4 是在弱酸条件下生产琥珀酸的有希望的候选者。从长链脂肪酸到中链脂肪酸的变化可能会降低 H+ 进入细胞质的渗透性，以便在酸胁迫下生存。这些结果表明 A. succinogenes BC-4 是在弱酸条件下生产琥珀酸的有希望的候选者。从长链到中链脂肪酸的变化可能会降低 H+ 进入细胞质的渗透性，以便在酸胁迫下生存。这些结果表明 A. succinogenes BC-4 是在弱酸条件下生产琥珀酸的有希望的候选者。