Bacillus cereus MHI 86 and Bacillus thuringiensis 5-29 both produce the antilisterial bacteriocin thuricin S – analysis of antimicrobial spectrum, stability, and producer strain suitability, including cytotoxicity evaluation

Thuricin-like bacteriocins are known for their potent antibacterial properties. This study characterizes thuricin S from Bacillus (B.) cereus MHI 86 and B. thuringiensis 5–29 previously isolated from foods. Cell-free supernatants and partially purified thuricin S exhibited antibacterial activity against Gram-positive species, including Listeria and Bacillus . Thuricin S production started at mid exponential growth phase. Minimum inhibitory concentrations against L. monocytogenes were 5.73 µg/mL (MHI 86) and 10.77 µg/mL (5–29). Both genomes harbor thuricin S-encoding open reading frames. From 8 h of growth, transcription of the bacteriocin gene cluster was consistently detected with most prominent bands at 120 bp. Accordingly, antibacterially active peptides were found at ~ 3.1 kDa, consistent with the size of thuricin S. Ultra-performance liquid chromatography-electrospray ionization mass spectrometry confirmed the molecular mass of the partially purified peptides as 3137.6 Da. The bacteriocins were active at neutral and acidic pH (3–7) and up to 80°C. In conclusion, this study is the first to provide a comparative characterisation of thuricin S in two different Bacillus spp. It sheds light on the genetic and transcriptional basis of thuricin S production, as well as its growth and production kinetics, antimicrobial activity, molecular weight, stability, and associated toxin production and cytotoxicity. Notably, thuricin S can be used as a natural agent against L. monocytogenes to control post-pasteurisation contamination.