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Characterization of a higBA Toxin-Antitoxin Locus in Vibrio cholerae

Priya Prakash Budde ,^1,2,, Brigid M. Davis,^2,* Jie Yuan,³ and Matthew K. Waldor^1,2,3

Department of Molecular Biology and Microbiology,² Program in Immunology, Tufts University School of Medicine,³ Howard Hughes Medical Institute, Boston, Massachusetts 02111¹

Received 23 June 2006/ Accepted 25 October 2006

Toxin-antitoxin (TA) loci, which were initially characterized as plasmid stabilization agents, have in recent years been detected on the chromosomes of numerous free-living bacteria. Vibrio cholerae, the causative agent of cholera, contains 13 putative TA loci, all of which are clustered within the superintegron on chromosome II. Here we report the characterization of the V. cholerae higBA locus, also known as VCA0391/2. Deletion of higA alone was not possible, consistent with predictions that it encodes an antitoxin, and biochemical analyses confirmed that HigA interacts with HigB. Transient exogenous expression of the toxin HigB dramatically slowed growth of V. cholerae and Escherichia coli and reduced the numbers of CFU by several orders of magnitude. HigB toxicity could be counteracted by simultaneous or delayed production of HigA, although HigA's effect diminished as the delay lengthened. Transcripts from endogenous higBA increased following treatment of V. cholerae with translational inhibitors, presumably due to reduced levels of HigA, which represses the higBA locus. However, no higBA-dependent cell death was observed in response to such stimuli. Thus, at least under the conditions tested, activation of endogenous HigB does not appear to be bactericidal.

Published ahead of print on 3 November 2006.

P.P.B. and B.M.D. contributed equally to this work.

Present address: Cell Press, 600 Technology Square, Cambridge, MA 02139.

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