Introduction:

In Escherichia coli, the type I toxin-antitoxin system tisB/istR-1 is part of the SOS response. Toxin gene tisB is strongly induced as soon as DNA damage occurs. TisB is a small hydrophobic protein located in the inner membrane, causing growth stasis due to depolarization and ATP depletion. TisB-induced dormancy favors formation of transiently multidrug-tolerant cells, so-called persisters.

Objectives:

The aim of this study was to investigate the role of protein aggregation in the recovery of persister cells in E. coli wild type MG1655.

Material and Methods:

We used the ScanLag method to monitor survival and recovery of TisB-dependent persister cells after ciprofloxacin treatment. In addition, protein aggregates were induced via heat stress (46°C). Fluorescence microscopy was performed using an ibpA-msfGFP reporter strain to verify protein aggregation.

Results:

We are able to demonstrate that ciprofloxacin triggers protein aggregation and that this process depends on TisB. Furthermore, we observe that persister cells of a tisB deletion strain resume growth faster than wild-type persisters. If heat stress is applied to induce protein aggregation in the tisB deletion strain, growth resumption is delayed and more similar to the wild type.

Conclusions:

Our experiments suggest that protein aggregates delay the recovery from the TisB-induced persister state. We conclude that formation of protein aggregates provides a means to stabilize persistence and probably dormancy in general.