Prevalence of Fst-like toxin-antitoxin systems

Toxin-antitoxin (TA) systems are widespread in Gram-negative bacteria, and all systems identified to date encode a toxic protein and an unstable antitoxin, which may be in the form of either an antisense RNA (type I) or a second protein (type II). The enterococcal plasmid pAD1-encoded TA system (par), encoding the Fst toxin, was the first type I TA system identified in Gram-positive bacteria (Weaver et al., 1996). In a recent issue of Microbiology, Weaver et al. (2009) identified an additional eight pAD1-like TA systems. Individual fst-like genes were identified on the chromosomes of Enterococcus faecalis, Lactobacillus casei and Staphylococcus saprophyticus strains, plasmids from E. faecalis, Lactobacillus curvatus and Staphylococcus aureus, and a phage from Lactobacillus gasseri. It was also hypothesized that the small size of Fst-like toxins may cause the failure of other members of the family to be recognized and annotated. We have now addressed this issue through iterative TBLASTN searching of the translated NCBI nucleotide sequence database (http://blast.ncbi.nlm.nih.gov/Blast.cgi).