Bojana Ilic1, Marko Đorđević2, Hong-Yu Ou3
1Institute of Physics Belgrade, National Institute of the Republic of Serbia, Serbia
2Faculty of Biology, University of Belgrade, Serbia
3Shanghai Jiao Tong University, Shanghai, China
bojanab [at] ipb.ac.rs
Abstract
Bacterial Type-II toxin-antitoxin (TA) systems, including kacAT in Klebsiella pneumoniae, respond to antibiotics. We investigated kacAT’s regulation relevant to antibiotic persistence, which refers to the survival of antibiotic exposure by dormant bacterial cells. Elevated toxin levels may induce dormancy. KacAT complex binds and represses the kacAT promoter cooperatively, leading to highly non-linear negative feedback. Antibiotics increase transcription of the kacA and kacT genes by inducing KacA degradation and consequently reducing the KacA:KacT ratio. Our model reproduced experimental findings, explaining increased kacAT transcription and reduced [KacA]:[KacT] ratio. Interestingly, KacAT overexpression induces antibiotic stress tolerance, while deleting kacAT has no effect, which our model can also explain. KacAT, therefore, cannot induce spontaneous (in the absence of antibiotics) persister formation. Earlier theoretical models, which predicted spontaneous persistence in Type-II TA systems, assumed the cooperative action of multiple TA systems. Our bioinformatics analysis, however, reveals a limited occurrence of multiple TA instances within clades and that cross-talk between clades is disfavored. These challenges the assumption of cooperativity in TA action, possibly explaining the absence of spontaneous persister generation in kacAT.
Keywords: Type II toxin-antitoxin systems; antibiotic persistence; systems biology; non-lienar dynamics; gene expression regulation; bioinformatics;
Acknowledgments: This work was supported by the Science and Technology Commission of Shanghai Municipality (grants no. 19430750600 and 19JC1413000), the National Natural Science Foundation of China (grant no. 32070572), the Medical Excellence Award funded by the Creative Research Development Grant from the First Affiliated Hospital of Guangxi Medical University (grant no. XK2019025), and the Science Fund of the Republic of Serbia (grant no. 7750294, q-bioBDS).
