MqsR/MqsA Toxin/Antitoxin System Regulates Persistence and Biofilm Formation in Pseudomonas putida KT2440

Abstract

Bacterial toxin/antitoxin (TA) systems have received increasing attention due to their prevalence, diverse structures, and important physiological functions. In this study, we identified and characterized a type II TA system in a soil bacterium <i>Pseudomonas putida</i> KT2440. This TA system belongs to the MqsR/MqsA family. We found that PP_4205 (MqsR) greatly inhibits cell growth in <i>P. putida</i> KT2440 and <i>Escherichia coli</i>, the antitoxin PP_4204 (MqsA) neutralizes the toxicity of the toxin MqsR, and the two genes encoding them are co-transcribed. MqsR and MqsA interact with each other directly <i>in vivo</i> and MqsA is a negative regulator of the TA operon through binding to the promoter. Consistent with the MqsR/MqsA pair in <i>E. coli</i>, the binding of the toxin MqsR to MqsA inhibits the DNA binding ability of MqsA in <i>P. putida</i> KT2440. Disruption of the <i>mqsA</i> gene which induces <i>mqsR</i> expression increases persister cell formation 53-fold, while overexpressing <i>mqsA</i> which represses <i>mqsR</i> expression reduces persister cell formation 220-fold, suggesting an important role of MqsR in persistence in <i>P. putida</i> KT2440. Furthermore, both MqsR and MqsA promote biofilm formation. As a DNA binding protein, MqsA can also negatively regulate an ECF sigma factor AlgU and a universal stress protein PP_3288. Thus, we revealed an important regulatory role of MqsR/MqsA in persistence and biofilm formation in <i>P. putida</i> KT2440.