Long-term survival of Escherichia coli lacking the HipBA toxin-antitoxin system during prolonged cultivation.

We designed and constructed six major toxin-antitoxin disruptants (Delta chpB1K, Delta dinj-yafQ, Delta hipBA, Delta mazEF, Delta relBE, and Delta yefM-yoeB) of Escherichia coli K-12 W3110. On prolonged cultivation of these disruptants with minimal M9 medium, the Delta hipBA cells exhibited a significantly longer life span than that of the other disruptants and of wild-type cells, as analyzed with a LIVE/DEAD BacLight kit (Invitrogen, Carlsbad, CA) in combination with flow cytometry analysis. The gene expression level of hipA in the wild-type cells was highest at the stationary phase of 40 h. The Delta hipBA cells showed higher macromolecular synthesis activity than the wild-type cells at the stationary phase. Stationary phase cells of Delta hipBA and the wild-type strain showed a significantly extended life span under anaerobic conditions. Furthermore, the Delta hipBA cells showed higher resistance to H2O2 than the wild type. These results suggest that HipBA induces cell death with oxidative stress during prolonged cultivation. This is the first report that an E. coli toxin-antitoxin (TA) system affects frequency of survival during the long-term stationary phase.