disrupts -host dynamics in the domestic mite : evidence from manipulative experiments.

UNLABELLED

We investigated the tripartite interactions between two intracellular bacterial symbionts, and in . Cultures of are typically single-infected by one intracellular symbiont. However, co-infection can be experimentally induced by mixing single-infected cultures, resulting in 10% of mite individuals being double-infected () and a corresponding reduction in host fitness. Here, we assembled the genomes of and and analyzed their gene expression in parental single-infected and mixed mite cultures using population-level samples (ranging from 7,500 to 10,000 mites). interacts more extensively with its mite host than in single-infected cultures. However, in mixed cultures, (i) exhibited reduced regulation of the host compared with ; (ii) the gene expression profile of shifted, increasing its interactions with the host, whereas the gene expression profile of remained unchanged; and (iii) genes exhibited a loss of interactions with mite gene expression, as indicated by reduced correlations (for example with host MAPK, endocytosis, and calcium signaling pathways). The experiments show that at the mite population level, symbiont infection disrupts gene expression interaction between the two symbionts and their host in different ways. was more influenced by gene expression than vice versa. can inhibit the growth of by disrupting its interaction with the host, leading to a loss of influence on mite immune and regulatory pathways. The reasons for responses are due to co-infection or the reduced frequency of single-infected individuals due to the analyses of population-level samples.

IMPORTANCE

We found that disrupts the interaction between and mite host. In single-infected cultures, strong correlations exist between symbiont and host gene expressions. Interestingly, although can also interact with the host, this interaction appears weaker compared with in single-infected cultures. These results suggest that both symbionts affect mite host gene expression, particularly in immune and regulatory pathways. In mixed samples, appears to outcompete by disrupting its host interaction. It indicates competition between these two intracellular symbionts in mite populations. belongs to a mite-specific supergroup Q, distinct from the more commonly studied 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.