Accepted_test

Antibiotic persistence refers to a phenomenon in which a small subpopulation of bacterial cells (dormant cells) survives antibiotic treatment despite being genetically identical to the vast majority of cells that are susceptible to antibiotics. Bacterial Type-II toxin-antitoxin (TA) systems, such as kacAT in Klebsiella pneumoniae, respond to antibiotic exposure, where elevated toxin levels may induce dormancy. We investigate kacAT's regulation when exposed to antibiotics. The KacAT complex binds and represses the kacAT promoter cooperatively, resulting in highly non-linear negative feedback. Our mechanistic model explains experimental findings, such as: i) Increased kacAT transcription, and ii) reduced [KacA]:[KacT] ratio, which is a consequence of drug induced degradation of KacA. Interestingly, KacAT overexpression induces tolerance to antibiotic exposure, while deleting kacAT has no effect, which our model could also explain. Consequently, KacAT, cannot induce spontaneous (no antibiotics present) persister formation, in accordance with recent experimental evidence for different Type-II TA systems, but contrary to earlier theoretical models. These models assumed the cooperative action of multiple TA systems. However, our bioinformatics analysis reveals rare occurrence of multiple TA instances within clades and that cross-talk between clades is disfavored. These question the assumption of cooperativity in TA action, possibly explaining the nonappearance of spontaneous persister formation in kacAT.