Journal
MOLECULAR MICROBIOLOGY
Volume 107, Issue 6, Pages 734-746Publisher
WILEY
DOI: 10.1111/mmi.13911
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Funding
- Biotechnology and Biosciences Research Council (UK) Institute Strategic Programme [BB/J004561/1, BB/P012523/1]
- Natural Sciences and Engineering Research Council of Canada [435784-2013]
- Science Foundation Ireland Investigator Award [13/IA/1875]
- Biotechnology and Biological Sciences Research Council [BBS/E/J/000PR9791, BBS/E/J/00000201] Funding Source: researchfish
- BBSRC [BBS/E/J/000PR9791] Funding Source: UKRI
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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 F1F0 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(R)) 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(R) 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.
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