DNA supercoiling is essential for all living cells because it controls all processes involving DNA. In bacteria, global DNA supercoiling results from the opposing activities of topoisomerase I, which relaxes DNA, and DNA gyrase, which compacts DNA. These enzymes are widely conserved, sharing >91% amino acid identity between the closely related species Escherichia coli and Salmonella enterica serovar Typhimurium. Why, then, do E . coli and Salmonella exhibit different DNA supercoiling when experiencing the same conditions? We now report that this surprising difference reflects disparate activation of their DNA gyrases by the polyamine spermidine and its precursor putrescine. In vitro , Salmonella DNA gyrase activity was sensitive to changes in putrescine concentration within the physiological range, whereas activity of the E . coli enzyme was not. In vivo , putrescine activated the Salmonella DNA gyrase and spermidine the E . coli enzyme. High extracellular Mg 2+ decreased DNA supercoiling exclusively in Salmonella by reducing the putrescine concentration. Our results establish the basis for the differences in global DNA supercoiling between E . coli and Salmonella , define a signal transduction pathway regulating DNA supercoiling, and identify potential targets for antibacterial agents. Author summary Living organisms are capable of altering the structure of their DNA in a process called DNA supercoiling. The amount of global DNA supercoiling in bacteria changes depending on environmental and metabolic conditions. Even closely related bacterial species differ in global DNA supercoiling and how it is regulated. Here, we elucidate a mechanism responsible for the discrepancies in global DNA supercoiling between E . coli and S . Typhimurium. We determine that different polyamines regulate in vivo DNA supercoiling in the two organisms: spermidine in E . coli and putrescine in S . Typhimurium. In addition, we show that only S . Typhimurium alters global DNA supercoiling in response to changes in extracellular Mg 2+ concentration, and that it does so by modifying putrescine abundance. Our results indicate that differences in the control of shared metabolic pathways can give rise to differences in global DNA supercoiling between closely related bacterial species. Moreover, they suggest ways to inhibit DNA supercoiling in pathogens without impacting commensals or humans.
【초록키워드】 activity, DNA, polyamines, pathogen, humans, Control, pathway, target, Pathogens, Bacteria, in vivo, Enzymes, change, mechanism, Signal transduction, Salmonella, Amino acid, Concentration, regulate, metabolic pathways, Escherichia coli, physiological, putrescine, spermidine, identity, Activation, metabolic pathway, enzyme, organism, precursor, discrepancies, discrepancy, polyamine, bacterial species, topoisomerase, DNA supercoiling, Alter, Extracellular, metabolic conditions, responsible, identify, conserved, addition, inhibit, activated, determine, changes in, reducing, regulated, disparate, reflect, living cell, bacterial specy, E . coli, gyrase, 【제목키워드】 DNA, Activation, disparate, gyrase,