Functioning of the TA cassette of streptococcal plasmid pSM19035 in various Gram-positive bacteria.

Abstract Toxin–antitoxin (TA) systems are common in microorganisms and are frequently found in the chromosomes and low-copy number plasmids of bacterial pathogens. One such system is carried by the low copy number plasmid pSM19035 of the pathogenic bacterium Streptococcus pyogenes . This plasmid encodes an omega - epsilon - zeta cassette that ensures its stable maintenance by post-segregational killing of plasmid-free cells. In this study, the activity of the ω - e - ζ cassette was examined in various Gram-positive bacteria with a low G/C content in their DNA. The broad host range of pSM19035 was confirmed and the copy number of a truncated derivative in transformed strains was determined by real-time qPCR.