Active stable maintenance functions in low copy-number plasmids of Gram-positive bacteria II. Post-segregational killing systems.

Active support is needed for low copy-number plasmids to be stably maintained in bacterial cells. The mechanisms that fulfill this role are (i) partition systems (PAR) acting to separate plasmid molecules to daughter cells and (ii) toxin-andidote (TA) (post-segregational killing-PSK) systems which arrest cell growth until the plasmid reaches the correct copy-number or kill the cells that have not inherited the plasmid. Our knowledge of toxin-antidote systems comes mainly from studies on Gram-negative bacteria. However, some addiction systems of Gram-positive bacteria have been characterized in detail or recently identified. Altogether, they bring new interesting data on toxin-antidote functioning in bacteria.