Model cyanobacterial consortia reveal a consistent core microbiome independent of inoculation source or cyanobacterial host species

Cyanobacteria are central to biogeochemical cycling, climate change, and eutrophication. While they readily develop associations with environmental microorganisms, the question of whether they consistently recruit specific microbiomes remains unresolved. Here, we established in vitro cyanobacterial consortia by inoculating five different cyanobacterial strains with microbiomes from three freshwater environments to determine if similar non-cyanobacterial organisms were recruited into stable cyanobacteria-based communities. Using amplicon and genome-resolved metagenomic methods we determined that stable cyanobacterial communities largely share the same taxa, regardless of the host cyanobacterial species or inoculation source. Specifically, we identified a 25 species core microbiome, which was significantly enriched in functions for micronutrient biosynthesis, metabolite transport/exchange, and anoxygenic photosynthesis. Furthermore, core species were enriched in putative mobile genetic elements, including two large (> 100 kb) circularized and curated plasmids, encoding functions that may support cyanobacteria-heterotroph symbioses. The consistency observed across these systems indicate that cyanobacterial consortia maintained under similar conditions converge to a predictable structure, and support a core microbiome with taxonomic and functional similarity to core microbiomes of other phototroph-heterotroph symbiotic assemblages. ### Competing Interest Statement The authors have declared no competing interest.