BetaH proteolysis unleashes an electrostatic-homing antibacterial polymorphic toxin

Area of Science:

• Microbiology
• Bacterial Competition
• Molecular Biology

Background:

• Polymorphic toxin systems (PTSs) are crucial for bacterial competition, but experimental data in Gram-positive bacteria are scarce.
• Diverse PTSs have been identified across bacterial phyla, highlighting their ecological significance.

Purpose of the Study:

• To characterize a diffusible PTS from Staphylococcus aureus (S8-Ntox35).
• To investigate the mechanism of inter-genus antagonism against Listeria monocytogenes.
• To elucidate the role of extracellular processing and specific bacterial transporters in PTS activity.

Main Methods:

• Genetic characterization of the S8-Ntox35 locus in Staphylococcus aureus.
• Assays to determine inter-genus antagonism against Listeria monocytogenes.
• Experimental evolution to identify bacterial resistance mechanisms.
• Analysis of cationic antimicrobial peptide (CAMP) resistance pathways (DltABCD, MprF) and ABC transporters (AnrAB).

Main Results:

• The S8-Ntox35 system mediates antagonism against Listeria monocytogenes via a heat-labile protein.
• Extracellular cleavage of the BetaH domain by an S8 peptidase produces a CAMP-like peptide essential for toxicity.
• The Ntox35 RNase domain is responsible for intoxication, with target cell resistance influenced by CAMP defense pathways.
• The ABC transporter AnrAB is essential for intoxication, and its disruption abolishes susceptibility while increasing sensitivity to the BetaH domain.

Conclusions:

• A novel mechanism of inter-genus antagonism among Firmicutes is revealed.
• Extracellular processing and ABC transporter-mediated susceptibility are key functional roles in PTS activity.
• This study expands the repertoire of diffusible toxins in Gram-positive bacteria and provides a foundation for further research on S8-PTS systems.