<i>Cardinium</i> disrupts <i>Wolbachia</i> –host dynamics in the domestic mite <i>Tyrophagus putrescentiae</i> : evidence from manipulative experiments

We found that <i>Cardinium</i> disrupts the interaction between <i>Wolbachia</i> and mite host. In <i>Wolbachia</i> single-infected cultures, strong correlations exist between symbiont and host gene expressions. Interestingly, although <i>Cardinium</i> can also interact with the host, this interaction appears weaker compared with <i>Wolbachia</i> in single-infected cultures. These results suggest that both symbionts affect mite host gene expression, particularly in immune and regulatory pathways. In mixed samples, <i>Cardinium</i> appears to outcompete <i>Wolbachia</i> by disrupting its host interaction. It indicates competition between these two intracellular symbionts in mite populations. <i>Wolbachia</i> belongs to a mite-specific supergroup Q, distinct from the more commonly studied <i>Wolbachia</i> supergroups. As these mite-specific bacteria exhibit pathogen-blocking effects, our findings may have relevance for other systems, such as ticks and tick-borne diseases. The study sheds light on intracellular symbiont interaction within a novel mite-symbiont model.