Host specific microbiome assembly and phylosymbiotic patterns in microalgae

Microalgae and their microbiome are foundational to marine ecosystems, driving carbon cycling and supporting microbial communities. However, the host specificity of microalgal microbiomes and the potential for phylosymbiotic relationships remain unclear. In this study, we analyzed the microbiomes of six microalgal species, including dinoflagellates and diatoms, across multiple strains and growth stages. Our results reveal distinct host-specific microbiomes, with dinoflagellates exhibiting stronger host filtering and higher numbers of core and host-specific operational taxonomic units (OTUs) compared to diatoms. Phylosymbiotic patterns were observed, where microbiome composition closely followed the evolutionary relationships of the host algae. Deterministic processes, particularly host genotype, were the dominant factors shaping microbiome assembly, overriding environmental influences. These findings demonstrate that microalgal microbiomes are tightly linked to host identity, suggesting a significant ecological and evolutionary role for host-microbiome interactions in marine environments. This study highlights the need to integrate both microbial and host factors in understanding marine ecosystem dynamics.