Identification and characterization of a toxin-antitoxin system on plasmid pRC18

HARO CECILIA; ARISTIMUÑO FICOSECO MARÍA; STEPANENKO TATIANA; OLAYA PASARELL MARÍA; VIGNOLO GRACIELA; RAYA RAÚL

Tucumán, Argentina

Congreso; SAIB XLV reunión Anual- Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2009

Sociedad Argentina de Investigación en Bioquímica y Biologái Molecular

A plasmid-borne toxin-antitoxin (TA) system is composed of a stable toxin protein and an unstable antitoxin component and helps in plasmid maintenance by killing of plasmid-free segregants. The lactic acid bacterium Lactobacillus curvatus CRL 705 harbors plasmid pRC18, which is associated with the production of lactocin Lac705, a two-component bacteriocin. Although several plasmid-curing protocols have been applied to strain CRL705, no pRC18-cured derivative has been yet isolated; in some lactocin Lac705-negative mutants, plasmid pRC18 seems to undergo structural rearrangements and be in low copy-number (i.e., strain Sac7).  In this study, we describe the presence of a putative TA module (partitioning locus) on plasmid pRC18, which is organized in a single operon that produces a 92-amino-acids antitoxin (orf4) and a 118-amino-acids toxin (orf3); these proteins belong, respectively, to the PhdYeFM and COG3041 superfamilies. Plasmid maintenance functions of the putative TA locus on pRC18 may explain the remarkable stability of this plasmid.