Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College Dublin, Dublin 2, Ireland.
Department of Biology, Institute for Microbial Systems and Society, University of Regina, Regina, SK, S4S 0A2, Canada.
Mol Microbiol. 2018 Mar;107(6):734-746. doi: 10.1111/mmi.13911. Epub 2018 Feb 5.
DNA in intracellular Salmonella enterica serovar Typhimurium relaxes during growth in the acidified (pH 4-5) macrophage vacuole and DNA relaxation correlates with the upregulation of Salmonella genes involved in adaptation to the macrophage environment. Bacterial ATP levels did not increase during adaptation to acid pH unless the bacterium was deficient in MgtC, a cytoplasmic-membrane-located inhibitor of proton-driven F F ATP synthase activity. Inhibiting ATP binding by DNA gyrase and topo IV with novobiocin enhanced the effect of low pH on DNA relaxation. Bacteria expressing novobiocin-resistant (Nov ) derivatives of gyrase or topo IV also exhibited DNA relaxation at acid pH, although further relaxation with novobiocin was not seen in the strain with Nov gyrase. Thus, inhibition of the negative supercoiling activity of gyrase was the primary cause of enhanced DNA relaxation in drug-treated bacteria. The Salmonella cytosol reaches pH 5-6 in response to an external pH of 4-5: the ATP-dependent DNA supercoiling activity of purified gyrase was progressively inhibited by lowering the pH in this range, as was the ATP-dependent DNA relaxation activity of topo IV. We propose that DNA relaxation in Salmonella within macrophage is due to acid-mediated impairment of the negative supercoiling activity of gyrase.
细胞内的沙门氏菌血清型鼠伤寒在酸性（pH4-5）巨噬细胞小泡中生长时松弛，并且 DNA 松弛与沙门氏菌基因的上调相关，这些基因参与适应巨噬细胞环境。除非细菌缺乏细胞质膜定位的质子驱动 F F ATP 合酶活性抑制剂 MgtC，否则在适应酸性 pH 时细菌的 ATP 水平不会增加。用新生霉素抑制 DNA 拓扑异构酶 II 和拓扑异构酶 IV 与 ATP 的结合增强了低 pH 对 DNA 松弛的影响。表达耐新生霉素（Nov）的拓扑异构酶 II 或拓扑异构酶 IV 衍生物的细菌在酸性 pH 下也表现出 DNA 松弛，尽管在 Nov 拓扑异构酶 II 菌株中未见用新生霉素进一步松弛。因此，抑制拓扑异构酶 II 的负超螺旋活性是药物处理细菌中增强 DNA 松弛的主要原因。沙门氏菌细胞质在响应外部 pH4-5 时达到 pH5-6：纯化的拓扑异构酶 II 的 ATP 依赖性 DNA 超螺旋活性在该范围内随着 pH 的降低而逐渐受到抑制，拓扑异构酶 IV 的 ATP 依赖性 DNA 松弛活性也是如此。我们提出，巨噬细胞内沙门氏菌中的 DNA 松弛是由于酸介导的拓扑异构酶 II 的负超螺旋活性受损所致。
