Experimental evolution of a pathogen confronted with innate immune memory increases variation in virulence

Area of Science:

• Evolutionary biology
• Epidemiology
• Pathogen evolution

Background:

• Virulence evolution is driven by pathogen fitness trade-offs and host responses like resistance and tolerance.
• Pathogen evolution is traditionally studied under adaptive immunity, with less known about evolution under innate immune priming.

Purpose of the Study:

• To investigate how innate immune priming in red flour beetles influences the evolution of their bacterial pathogen, Bacillus thuringiensis tenebrionis.
• To understand the genetic and phenotypic changes in pathogens evolving under host immune memory.

Main Methods:

• Experimental evolution of Bacillus thuringiensis tenebrionis in primed versus non-primed red flour beetles.
• Measurement of pathogen virulence and assessment of host resistance.
• Whole genome sequencing to identify genetic changes in evolved pathogen lines.

Main Results:

• No significant change in average pathogen virulence was observed in primed hosts.
• A significant increase in the variability of virulence among pathogen lines evolved in primed hosts.
• Pathogens did not evolve resistance to host immune priming; increased mobilome activity (prophages, plasmids) was noted.
• Cry toxin expression linked to plasmid copy number variation, but not directly to virulence.

Conclusions:

• Innate immune memory can drive increased variability in pathogen traits, potentially enhancing adaptation to diverse environments.
• Understanding pathogen evolution under innate immune priming is crucial for applications in medicine, pest control, and agriculture.