RESUMO
Metabolically quiescent bacteria represent a large proportion of those in natural and host environments, and they are often refractory to antibiotic treatment. Such drug tolerance is also observed in the laboratory during stationary phase, when bacteria face stress and starvation-induced growth arrest. Tolerance requires (p)ppGpp signaling, which mediates the stress and starvation stringent response (SR), but the downstream effectors that confer tolerance are unclear. We previously demonstrated that the SR is linked to increased antioxidant defenses in Pseudomonas aeruginosa We now demonstrate that superoxide dismutase (SOD) activity is a key factor in SR-mediated multidrug tolerance in stationary-phase P. aeruginosa Inactivation of the SR leads to loss of SOD activity and decreased multidrug tolerance during stationary phase. Genetic or chemical complementation of SOD activity of the ΔrelA spoT mutant (ΔSR) is sufficient to restore antibiotic tolerance to WT levels. Remarkably, we observe high membrane permeability and increased drug internalization upon ablation of SOD activity. Combined, our results highlight an unprecedented mode of SR-mediated multidrug tolerance in stationary-phase P. aeruginosa and suggest that inhibition of SOD activity may potentiate current antibiotics.
Assuntos
Farmacorresistência Bacteriana Múltipla , Pseudomonas aeruginosa/efeitos dos fármacos , Superóxido Dismutase/metabolismo , Antibacterianos/farmacologia , Relação Dose-Resposta a Droga , Gentamicinas/farmacologia , Ligases/metabolismo , Meropeném , Testes de Sensibilidade Microbiana , Ofloxacino/farmacologia , Pseudomonas aeruginosa/enzimologia , Transdução de Sinais , Superóxido Dismutase/fisiologia , Tienamicinas/farmacologiaRESUMO
Saccharomyces species have five TPO genes, TPO1 through TPO5, coding for proteins that are involved in up taking or excreting intracellular spermine, putrescine or spermidine. Here, we investigate the evolutionary fate and functional impacts of gene conversions between these genes. Our results show that gene conversions occurred only between the TPO2 and TPO3 genes of the six Saccharomyces species we studied. They also show that these gene conversions occurred independently in all six species. The facts that they only occur between closely related genes having similar function, and that they are limited to the transmembrane domain of these proteins, suggest that they have little functional impact. These gene conversions therefore likely represent neutral mutations which are not subject to purifying selection.