Gut Bacteriome Modulation in Rhipicephalus microplus Under Biotic Stress From Metarhizium anisopliae and Anaplasma marginale

Understanding how multiple biotic stressors shape host‐associated bacteriomes is essential for predicting ecological outcomes. This study examined interactions among the cattle tick Rhipicephalus microplus , the pathogen Anaplasma marginale and the entomopathogenic fungus Metarhizium anisopliae . Across treatments involving fungal exposure alone or combined with A. marginale , the gut bacteriome comprised 698 ASVs, of which 28.2% formed a stable core dominated by Bacteroidota and Bacillota. Fungal‐associated stress drove functional shifts, including enrichment of SCFA‐producing taxa such as Akkermansia muciniphila and Lachnospiraceae , indicating reorganization preceding major taxonomic changes. Co‐occurrence networks were restructured under fungal and combined pressures, showing high connectivity, predominance of negative correlations and antagonistic interactions driven by keystone taxa like Prevotella . The combined‐stressor network showed greater robustness, cohesion and communication efficiency than single‐stressor conditions. Functional predictions revealed conserved metabolic profiles, yet co‐exposure increased functional diversity and gene abundance, with A. marginale exerting dominant influence. In silico removal of A. marginale from the co‐exposure condition indicated a persistent ecological imprint, preventing reversion to the basal fungal‐only configuration and retaining structural traces of prior colonization. Overall, simultaneous pathogen–fungus pressures reorganize microbial networks, tightening interactions and enhancing stability, underscoring the dual role of M. anisopliae as a biocontrol agent and potential modulator of bacteriome resilience.