Toxin ζ Reversible Induces Dormancy and Reduces the UDP-N-Acetylglucosamine Pool as One of the Protective Responses to Cope with Stress

Toxins of the zeta/PezT family, found in the genome of major human pathogens, phosphorylate the peptidoglycan precursor uridine diphosphate-N-acetylglucosamine (UNAG) leading to unreactive UNAG-3P. Transient over-expression of a PezT variant impairs cell wall biosynthesis and triggers autolysis in Escherichia coli. Conversely, physiological levels of zeta reversibly induce dormancy produce a sub-fraction of membrane-compromised cells, and a minor subpopulation of Bacillus subtilis cells become tolerant of toxin action. We report here that purified zeta is a strong UNAG-dependent ATPase, being GTP a lower competitor. In vitro, zeta toxin phosphorylates a fraction of UNAG. In vivo, zeta-mediated inactivation of UNAG by phosphorylation does not deplete the active UNAG pool, because expression of the toxin enhances the efficacy of genuine cell wall inhibitors (fosfomycin, vancomycin or ampicillin). Transient zeta expression together with fosfomycin treatment halt cell proliferation, but epsilon(2) antitoxin expression facilitates the exit of zeta-induced dormancy, suggesting that there is sufficient UNAG for growth. We propose that zeta induces diverse cellular responses to cope with stress, being the reduction of the UNAG pool one among them. If the action of zeta is not inhibited, e.g., by de novo epsilon(2) antitoxin synthesis, the toxin markedly enhances the efficacy of antimicrobial treatment without massive autolysis in Firmicutes.