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pSM19035-encoded toxin induces stasis followed by death in a subpopulation of cells

¹ Department of Microbial Biotechnology, Centro Nacional de Biotecnología, CSIC, 28049 Madrid, Spain
² Max-Planck-Institut für molekulare Genetik, D-14195 Berlin, Germany
³ Institut für Mikrobiologie, Ernst-Moritz-Arndt-Universität, D-17487 Greifswald, Greifswald, Germany
⁴ Department of Food Safety Science, BBSRC Institute of Food Research, Norwich Laboratory, Colney Lane, Norwich Research Park, Colney, Norwich NR4 7UA, UK
⁵ University of Amsterdam, Swammerdam Institute of Life Sciences, 1018 WV Amsterdam, The Netherlands

Correspondence
Juan C. Alonso
jcalonso{at}cnb.uam.es

The toxin–antitoxin operon of pSM19035 encodes three proteins: the global regulator, the labile antitoxin and the stable toxin. Accumulation of toxin free of antitoxin induced loss of cell proliferation in both Bacillus subtilis and Escherichia coli cells. Induction of a variant (Y83C) triggered stasis, in which B. subtilis cells were viable but unable to proliferate, without selectively affecting protein translation. In E. coli cells, accumulation of free toxin induced stasis, but this was fully reversed by expression of the antitoxin within a defined time window. The time window for reversion of toxicity by expression of antitoxin was dependent on the initial cellular level of . After 240 min of constitutive expression, or inducible expression of high levels of toxin for 30 min, expression of failed to reverse the toxic effect exerted by in cells growing in minimal medium. Under the latter conditions, inhibited replication, transcription and translation and finally induced death in a fraction (50 %) of the cell population. These results support the view that interacts with its specific target and reversibly inhibits cell proliferation, but accumulation of might lead to cell death due to pleiotropic effects.

This paper is dedicated to the memory of Piotr Ceglowski, who contributed so much to the advancement of pSM19035 biology.

A table of supplementary data is available with the online version of this paper.

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