Magnesium Links Starvation-Mediated Antibiotic Persistence to ATP

Bacterial persisters emerge and increase in numbers over time as a bacterial culture grows from log phase to stationary phase. However, the underlying basis of the inevitable tendency is unclear. In this study, we investigated the role of nutrients in starvation-mediated persister formation of Staphylococcus aureus. By screening of nutrient components, we found that starvation-induced persister formation of log-phase cultures could be reversed by addition of magnesium (Mg(2+)) but not amino acids, nucleotides, or other salts. Further, deprivation of extracellular Mg(2+) reduced cytoplasmic ATP, inducing persistence without affecting cytoplasmic Mg(2+) or membrane potential. Finally, we showed that Mg(2+) reduced expression of stationary cell marker genes, cap5A and arcA. These findings indicate a connection between Mg(2+) levels and ATP, which represents metabolic status and mediates antibiotic persistence during growth. IMPORTANCE Various genes have been identified to be involved in bacterial persister formation regardless of the presence or absence of persister genes. Despite recent discoveries of the roles of ATP and membrane potential in persister formation, the key element that triggers change of ATP or membrane potential remains elusive. Our work demonstrates that Mg(2+) instead of other ions or nutrient components is the key element for persistence by inducing a decrease of cytoplasmic ATP, which subsequently induces persister formation. In addition, we observed tight regulation of genes for Mg(2+) transport in different growth phases in S. aureus. These findings indicate that despite being a key nutrient, Mg(2+) also served as a key signal in persister formation during growth.