Do Interactions among Microbial Symbionts Cause Selection for Greater Pathogen Virulence?

Area of Science:

• Microbial ecology
• Evolutionary biology
• Plant pathology

Background:

• Microbiome treatments are increasingly used for disease control in agriculture and medicine.
• The evolutionary impacts of these treatments on pathogen fitness and virulence are poorly understood.
• Information on how symbionts affect pathogen fitness is crucial for predicting disease evolution.

Purpose of the Study:

• To investigate the fitness consequences of a plant pathogen, Ustilago maydis, under varying virulence levels.
• To assess the impact of a defensive symbiont, Fusarium verticillioides, on pathogen fitness when coinfecting the host plant Zea mays.
• To determine how symbiont presence influences the evolution of pathogen virulence.

Main Methods:

• Statistical modeling was used to estimate fitness consequences for Ustilago maydis.
• Fitness was assessed across different virulence levels in the presence and absence of Fusarium verticillioides.
• Virulence was quantified as the reduction in host plant growth caused by infection.

Main Results:

• The defensive symbiont significantly reduced pathogen infection and subsequent disease development.
• Pathogen fitness was lower across all virulence levels when the defensive symbiont was present.
• The optimal virulence level for maximal pathogen fitness was higher in the presence of the defensive symbiont.

Conclusions:

• Competition with defensive symbionts can select for increased pathogen virulence, aligning with theories of multiple parasite infections.
• The evolutionary outcomes of pathogen-microbe interactions are context-dependent and influenced by environmental factors.
• Interactions within diverse microbial communities contribute to the maintenance of symbiotic functions.