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Reactive oxygen species contribute to the bactericidal effects of the fluoroquinolone moxifloxacin in Streptococcus pneumoniae: metabolic pathways involved

ABSTRACT: We studied the transcriptomic response of S. pneumoniae to moxifloxacin, a fluoroquinolone that inhibits DNA gyrase. At 10 × MIC, 30 and 140 responsive genes were detected at 15 and 30 minutes, respectively. Several pathways leading to an increase in pyruvate showed up-regulation. These included 2 genes introducing P-sugars into the glycolysis and 3 out of 7 genes of the glycolysis pathway, which converts fructose-6P to pyruvate. In addition, an increase in acetyl-coA would be expected from the down-regulation of the genes coding for the acetyl-coA carboxylase, and in turn, to a further increase in pyruvate by the up-regulation of formate acetyltransferase. Since pyruvate is converted to hydrogen peroxide (H2O2) by pyruvate oxidase (SpxB), its increase would lead to an equivalent increase in the intracellular amount of H2O2, and in turn, in those of hydroxyl radicals resulting from the Fenton reaction, which damage DNA, lipids and proteins. We observed similar increases in the production of H2O2 and hydroxyl radicals under moxifloxacin treatment. These reactive oxygen species contributed to the lethality of the drug, as showed by the attenuation of its lethality in a strain lacking SpxB. These results support the production of redox alterations by fluoroquinolones and are in agreement with our previous findings showing that levofloxacin, an inhibitor of topoisomerase IV, triggers the transcriptional activation of iron transport genes. Both fluoroquinolones stimulate the Fenton reaction in their mechanism of action, by increasing the amounts of any of their two components: iron by levofloxacin or H2O2 by moxifloxacin.

ORGANISM(S): Streptococcus pneumoniae R6

PROVIDER: GSE68947 | GEO | 2016/02/05

SECONDARY ACCESSION(S): PRJNA284149

REPOSITORIES: GEO

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Project description:Pyruvate oxidase encoded by spxB is a major virulence factor in the human respiratory pathogen Streptococcus pneumoniae. During aerobic growth, SpxB synthesizes large amounts of H2O2 and acetyl phosphate, which can serve as a phosphoryl group donor to response regulators and be converted to ATP. SpxB is the main source of the millimolar concentrations of H2O2 produced and tolerated by pneumococcus, despite its lack of a catalase. We report here the first cis- and trans-acting regulatory elements for spxB transcription. These elements were identified in a genetic screen, similar to those used previously for phase variants, for spontaneous mutations that caused colonies of virulent serotype 2 strain D39 to change from a transparent to an opaque appearance. Six of the seven opaque colonies recovered (frequency of 3 x 10-5) were impaired for SpxB function. Modeling suggested that two mutations changed amino acids in SpxB required for FAD cofactor or subunit binding. One mutation deleted a cis-acting adjacent direct repeat required for optimal spxB transcription. The other three independent mutations created the same frameshift near the start of a trans-acting regulatory gene designated as spxR. The SpxR protein contains helix-turn-helix, CBS, and HotDog domains implicated in DNA, adenosine, and CoA compound binding, respectively, consistent with the idea that SpxR positively regulates spxB transcript amount in response to energy and metabolic state rather than oxidative state. Finally, microarray analyses of a null spxB or a spxR mutant revealed the presence of a new oxidative stress response in pneumococcus and unexpectedly demonstrated that SpxR strongly positively regulates the transcript amount of the strH exoglycosidase gene, which like spxB, has been implicated in host colonization. Keywords: genetic modification Bacterial strains were grown exponentially in rich (BHI) media at 37C and an atmosphere of 5% CO2, and were processed as described in the related Sample records. Samples were collected from three independent biological replicates and included one dye swap. Data were normalized using the Lowess (subgrid) method without background subtraction.

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Reactive oxygen species contribute to the bactericidal effects of the fluoroquinolone moxifloxacin in Streptococcus pneumoniae: metabolic pathways involved

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