MICROBIOLOGY: Patchwork Plasmid Poison

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Science  21 Mar 2003:
Vol. 299, Issue 5614, pp. 1815d
DOI: 10.1126/science.299.5614.1815d

Gram-positive bacteria, such as Enterococcus faecium, are sources of hospital-acquired infection and are dangerous vehicles for antibiotic resistance plasmids. Little is known about the mechanisms by which such plasmids are maintained in Gram-positive bacteria. Grady and Hayes have discovered in the genetic patchwork that constitutes the multidrug-resistance plasmid pRUM a novel gene cassette encoding a protein toxin and cognate antitoxin: Axe-Txe. Toxin-antitoxin systems in Gram-negative bacteria ensure plasmid persistence in a population by inhibiting cells that do not possess the plasmid that encodes the antidote. Experimentally, Txe crosses the species boundary to inhibit the growth of Gram-negative Escherichia coli—this effect is reversed if expression of Axe is induced. Other homologs of Axe-Txe are widespread among bacteria, and E. coli itself possesses the YefM-YoeB pair. Bacteria producing Txe have a distinct filamentous phenotype, and it seems that Txe acts to inhibit cell division, although the cellular target is not yet known. — CA

Mol. Microbiol. 47, 1419 (2003).

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