IDENTIFICATION AND CHARACTERIZATION OF A TOXIN-ANTITOXIN SYSTEM ON PLASMID pRC18

CECILIA HARO; MARÍA C. ARISTIMUÑO FICOSECO; STEPANENKO TATIANA; MARÍA J. OLAYA PASSARELL; GRACIELA VIGNOLO; RAÚL R. RAYA

San Muguel de Tucumán

Congreso; XLV Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2009

Sociedad Argentina de investigación en Bioquímica y Biología 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 ofplasmid-free segregants. The lactic acid bacterium Lactobacillus curvatus CRL 705 harbors plasmid pRC18, which is associated with the production of lactocin Lac705, atwo-component bacteriocin. Although several plasmidcuring protocols have been applied to strain CRL705, no pRC18-cured derivative has been yet isolated; in somelactocin Lac705-negative mutants, plasmid pRC18 seems to undergo structural rearrangements and be in low copy-number (i.e., strain Sac7).In this study, we describethe 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 a118-amino-acids toxin (orf3); these proteins belong, respectively, to the superfamilies PhdYeFM and COG3041. Plasmid maintenance functions of the putative TA locuson pRC18 may explain the remarkable stability of this plasmid