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

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-ε-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.

► Plasmid pSM19035 and its derivatives can transform and replicate in clinically important Firmicutes strains.
► The plasmid copy number and stable maintenance are in part dependent on the properties of the host strain.
► The effectiveness of ω-ε-ζ TA cassette functioning is not correlated with the number of plasmid copies in studied strains.