Regulation of yefM/yoeB toxin antitoxin system is independent of ppGpp and inorganic polyphosphate in Escherichia coli.

Bacterial persistence is a phenomenon wherein small proportion of a bacterial population attains transient antibiotic tolerance likely by virtue of metabolic minimization. Type II Toxin-Antitoxin systems (TAs), small overlapping bicistronic negative auto-regulons, were recently shown to induce the persistence state. Maisonneuve et al., 2013 reported that TAs are activated by a regulatory cascade consisting of stochastic accumulation of ppGpp leading to accumulation of inorganic polyphosphate (polyP). PolyP supposedly is essential for Lon protease-dependent-degradation of antitoxins resulting in activation of toxins and induction of persistence phenotype. In contrast, using semi-quantitative primer extension, we show that transcriptional up-regulation of yefM/yoeB loci, one of the well characterized TAs of Escherichia coli, is independent of ppGpp and polyP. Similarly, we show that chromosome-encoded YoeB-dependent target mRNA cleavage is independent of polyP. Our results and meta-analysis of literature we conclude that the regulation of yefM/yoeB TAs is independent of ppGpp and polyP.