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Toxins 2015, 7(2), 299-321; doi:10.3390/toxins7020299

Orphan Toxin OrtT (YdcX) of Escherichia coli Reduces Growth during the Stringent Response

1
Department of Chemical Engineering, the Pennsylvania State University, University Park, PA 16802-4400, USA
2
Department of Biology, Texas A&M University, College Station, TX 77843-3258, USA
3
Department of Biochemistry and Molecular Biology, the Pennsylvania State University, University Park, PA 16802-4400, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Holger Barth
Received: 22 December 2014 / Accepted: 20 January 2015 / Published: 29 January 2015
(This article belongs to the Section Bacterial Toxins)
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Abstract

Toxin/antitoxin (TA) systems are nearly universal in prokaryotes; toxins are paired with antitoxins which inactivate them until the toxins are utilized. Here we explore whether toxins may function alone; i.e., whether a toxin which lacks a corresponding antitoxin (orphan toxin) is physiologically relevant. By focusing on a homologous protein of the membrane-damaging toxin GhoT of the Escherichia coli GhoT/GhoS type V TA system, we found that YdcX (renamed OrtT for orphan toxin related to tetrahydrofolate) is toxic but is not part of TA pair. OrtT is not inactivated by neighboring YdcY (which is demonstrated to be a protein), nor is it inactivated by antitoxin GhoS. Also, OrtT is not inactivated by small RNA upstream or downstream of ortT. Moreover, screening a genomic library did not identify an antitoxin partner for OrtT. OrtT is a protein and its toxicity stems from membrane damage as evidenced by transmission electron microscopy and cell lysis. Furthermore, OrtT reduces cell growth and metabolism in the presence of both antimicrobials trimethoprim and sulfamethoxazole; these antimicrobials induce the stringent response by inhibiting tetrahydrofolate synthesis. Therefore, we demonstrate that OrtT acts as an independent toxin to reduce growth during stress related to amino acid and DNA synthesis. View Full-Text
Keywords: toxin/antitoxin; orphan toxin; stringent response toxin/antitoxin; orphan toxin; stringent response
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Islam, S.; Benedik, M.J.; Wood, T.K. Orphan Toxin OrtT (YdcX) of Escherichia coli Reduces Growth during the Stringent Response. Toxins 2015, 7, 299-321.

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