Friend or foe? Functional roles of Ixodes ricinus microbes

The tick Ixodes ricinus is a major vector of multiple pathogens in Europe, yet the functional roles of its microbial communities and their impact on disease risk remain largely unexplored. Here, we propose a framework linking microbial transmission mode and microbial function to their effects on I. ricinus. We argue that transmission mode shapes the evolutionary pressures on microbes and, therefore, the nature and stability of their interactions with ticks. Building on the apparent absence of a single obligate nutritional symbiont in I. ricinus, we further propose that complementary and functionally redundant microbial traits may be more important than individual microbial taxa. This perspective provides a basis for understanding how microbiome function may influence tick adaptation, resilience, and ultimately disease risk.