BetaH proteolysis unleashes an electrostatic-homing antibacterial polymorphic toxin

Area of Science:

• Microbiology
• Bacterial competition
• Gram-positive bacteria

Background:

• Polymorphic toxin systems (PTSs) are crucial for bacterial competition, but experimental data in gram-positive bacteria are scarce.
• Previous studies primarily focused on gram-negative species, leaving the mechanisms in gram-positive bacteria largely unexplored.

Purpose of the Study:

• To mechanistically characterize a diffusible PTS in *Staphylococcus aureus*.
• To investigate its role in inter-genus antagonism against *Listeria monocytogenes*.
• To elucidate the molecular mechanisms of toxin activation and target cell susceptibility.

Main Methods:

• Characterization of the *Staphylococcus aureus* S8-Ntox35 locus.
• Assays to demonstrate inter-genus antagonism against *Listeria monocytogenes*.
• Experimental evolution to identify host factors involved in intoxication.
• Genetic manipulation of toxin and transporter genes.

Main Results:

• The S8-Ntox35 system mediates bactericidal antagonism against *Listeria monocytogenes*.
• Extracellular cleavage by S8 peptidase releases a cationic antimicrobial peptide (CAMP)-like domain, enhancing toxicity.
• The ATP-binding cassette (ABC) transporter AnrAB is essential for intoxication.
• Disruption of AnrAB confers resistance to Ntox35 but increases susceptibility to the CAMP-like domain.

Conclusions:

• This study reveals a novel mechanism of inter-genus bacterial antagonism mediated by a diffusible PTS in gram-positive bacteria.
• Extracellular processing and ABC transporter-dependent susceptibility are key features of this toxin system.
• The findings expand the understanding of bacterial competition and introduce a new avenue for investigating S8-PTS ecological roles.