Physical and Functional Interplay between MazF and Its Noncognate Antitoxins from Bifidobacterium longum.

strain JDM301, a widely used commercial strain in China, encodes at least two MazEF-like modules and one RelBE-like toxin-antitoxin (TA) system in its chromosome, designated MazEF, MazEF, and RelBE, respectively. Bacterial TA systems play an important role in several stress responses, but the relationship between these TA systems is largely unknown. In this study, the interactions between MazF and MazE or RelB were assessed in strain JDM301. MazF caused the degradation of mRNA, and its toxicity was inhibited by forming a protein complex with its cognate antitoxin, MazE Notably, MazF toxicity was also partially neutralized when jointly expressed with noncognate antitoxin MazE or RelB Our results show that the two noncognate antitoxins also inhibited mRNA degradation caused by MazF toxin. Furthermore, the physical interplay between MazF and its noncognate antitoxins was confirmed by immunoprecipitation. These results suggest that MazF can arrest cell growth and that MazF toxicity can be neutralized by its cognate and noncognate antitoxins. These results imply that JDM301 uses a sophisticated toxin-antitoxin interaction network to alter its physiology when coping with environmental stress. Although toxin-antitoxin (TA) systems play an important role in several stress responses, the regulatory mechanisms of multiple TA system homologs in the bacterial genome remain largely unclear. In this study, the relationships between MazEF and the other two TA systems of strain JDM301 were explored, and the interactions between MazF and MazE or RelB were characterized. In addition, the mRNA degradation activity of MazF was demonstrated. In particular, the interaction of the toxin with noncognate antitoxins was shown, even between different TA families (MazF toxin and RelB antitoxin) in JDM301. This work provides insight into the regulatory mechanisms of TA systems implicated in the stress responses of bifidobacteria.