The plant host environment influences competitive interactions between bacterial pathogens

Area of Science:

• Microbiology
• Plant Pathology
• Bacterial Genetics

Background:

• Bacteria utilize bacteriocins, narrow-spectrum protein antibacterials, for resource competition.
• Research on bacteriocin dynamics predominantly focuses on in vitro culture conditions, with limited exploration in host environments, especially plants.

Purpose of the Study:

• To investigate bacteriocin-mediated dynamics between bacterial strains within a plant host context.
• To determine the conditions under which bacteriocin production confers a fitness advantage to the producing bacterial strain in planta.

Main Methods:

• Co-inoculation of Pseudomonas syringae pv. syringae (Psy) and a bacteriocin-sensitive competitor, P. syringae pv. phaseolicola (Pph), in plant leaf apoplast and culture.
• Quantification of bacterial populations over time to assess growth and competitive interactions.
• Comparison of wild-type Psy with a bacteriocin-deficient mutant to evaluate the role of bacteriocin production.

Main Results:

• Psy expresses bacteriocin in both culture and leaf apoplast when co-inoculated with Pph.
• Bacteriocin negatively impacts the Pph population in both environments.
• A bacteriocin-mediated fitness benefit for Psy is observed only at low initial population frequency (1:9) in the leaf apoplast, leading to an eightfold population increase.
• No bacteriocin-mediated benefit for Psy was observed in culture.
• The observed benefit in planta is dependent on the Type III Secretion System.

Conclusions:

• Bacteriocin-mediated antagonism provides a fitness benefit to Pseudomonas syringae pv. syringae within the plant host, but this benefit is contingent on population dynamics and host environment.
• The Type III Secretion System is crucial for mediating this bacteriocin-induced fitness advantage in planta.
• These findings highlight the importance of host-pathogen interactions in shaping bacterial competitive strategies.