Increased Persistence in Escherichia coli Caused by Controlled Expression of Toxins or Other Unrelated Proteins

Abstract

Bacterial populations contain persisters, cells which survive exposure to bactericidal antibiotics and other lethal factors. Persisters do not have a genetic resistance mechanism, and their means to tolerate killing remain unknown. In exponentially growing populations of Escherichia coli the frequency of persister formation usually is 10 ؊7 to 10 ؊5 . It has been shown that cells overexpressing either of the toxic proteins HipA and RelE, both members of the bacterial toxin-antitoxin (TA) modules, have the ability to form more persisters, suggesting a specific role for these toxins in the mechanism of persistence. However, here we show that cells expressing proteins that are unrelated to TA modules but which become toxic when ectopically expressed, chaperone DnaJ and protein PmrC of Salmonella enterica, also form 100-to 1,000-fold more persisters. Thus, persistence is linked not only to toxicity caused by expression of HipA or dedicated toxins but also to expression of other unrelated proteins.

RETRACTED: Bacterial persistence by RNA endonucleases

“…Cells were grown in LB containing chloramphenicol (50 μg/mL) at 37°C. cases, toxin overproduction strongly increased the persister fraction with the two different antibiotics, thus supporting that the initial observations (32)(33)(34)(35) are generally valid (Fig. S3).…”

“…Although overproduction of mRNases appeared to induce a high level of persisters, certain unrelated proteins that become toxic when produced from plasmids have similar effects (35). Using relBE as a model system, we asked if an mRNase encoded by a TA locus could be activated to generate persisters.…”

“…Simultaneously, our observations allow us to propose a long sought after common function to TA loci. The combined observations that overproduction of mRNases induced a persister-like state (32,35) and that mRNase-induced stasis was reversible (30) prompted us to investigate the suggested connection between persistence and TA loci. We found strong evidence that TA loci encoding mRNases and the persistence phenomenon are intimately connected: Activation of endogenously encoded RelE and ectopic production of five mRNases induced antibiotic tolerance (Fig.…”

“…Cells overproducing TA-encoded mRNases were, similar to persister cells, tolerant to antibiotics (32)(33)(34)(35). Moreover, cell populations enriched for persisters had increased levels of TA mRNAs (33,34), and deletion of yafQ (encoding a RelE homolog) resulted in reduced persistence of cells in a biofilm but not in planktonic cells (32).…”

Regulation of phenotypic variability by a threshold-based mechanism underlies bacterial persistence

“…1A). Overexpression of the toxin was demonstrated to lead to a growth arrest that could be reversed by the expression of the antitoxin (23)(24)(25)(26). These findings confirm that the hipBA TA module plays a key role in determining bacterial persistence.…”