Helper bacteria halt and disarm mushroom pathogens by linearizing structurally diverse cyclolipopeptides

Area of Science:

• Microbiology
• Plant Pathology
• Biochemistry

Background:

• Pseudomonas tolaasii causes brown blotch disease in white button mushrooms.
• Tolaasin is the primary virulence factor, a pore-forming toxin.
• Helper bacteria, such as Mycetocola spp., may offer protection through unknown mechanisms.

Purpose of the Study:

• To elucidate the detoxification mechanism employed by Mycetocola spp. against Pseudomonas tolaasii toxins.
• To understand how helper bacteria protect mushrooms from brown blotch disease.
• To identify the enzymes and pathways involved in toxin inactivation.

Main Methods:

• Metabolic profiling
• Imaging mass spectrometry
• Structure elucidation
• Bioassays
• Activity-guided fractionation
• MALDI analyses
• Heterologous enzyme production

Main Results:

• Mycetocola spp. inactivate tolaasin by linearizing the lipocyclopeptide.
• Mycetocola spp. impair pathogen dissemination by cleaving the lactone ring of pseudodesmin.
• The gene cluster for pseudodesmin biosynthesis was identified and inactivated, confirming its role in swarming.

Conclusions:

• Mycetocola spp. possess an antivirulence strategy involving the degradation of key bacterial toxins.
• This tripartite interaction between fungus, helper bacteria, and pathogen has significant ecological and agricultural implications.
• The identified lactonase is responsible for cleaving pseudodesmin, inhibiting pathogen swarming.