Surface Topography, Bacterial Carrying Capacity, and the Prospect of Microbiome Manipulation in the Sea Anemone Coral Model Aiptasia

Abstract
Aiptasia is an emerging model organism to study cnidarian symbioses due to its taxonomic relatedness to other anthozoans such as stony corals and similarities of its microalgal and bacterial partners, complementing the existing Hydra (Hydrozoa) and Nematostella (Anthozoa) model systems. Despite the availability of studies characterizing the microbiomes of several natural Aiptasia populations and laboratory strains, knowledge on basic information, such as surface topography, bacterial carrying capacity, or the prospect of microbiome manipulation is lacking. Here we address these knowledge gaps. Our results show that the surface topographies of the model hydrozoan Hydra and anthozoans differ substantially, whereas the ultrastructural surface architecture of Aiptasia and stony corals is highly similar. Further, we determined a bacterial carrying capacity of ∼104 and ∼105 bacteria (i.e., colony forming units, CFUs) per polyp for aposymbiotic and symbiotic Aiptasia anemones, respectively, suggesting that the symbiotic status changes bacterial association/density. Microbiome transplants from Acropora humilis and Porites sp. to gnotobiotic Aiptasia showed that only a few foreign bacterial taxa were effective colonizers. Our results shed light on the putative difficulties of transplanting microbiomes between cnidarians in a manner that consistently changes microbial host association at large. At the same time, our study provides an avenue to identify bacterial taxa that exhibit broad ability to colonize different hosts as a starting point for cross-species microbiome manipulation. Our work is relevant in the context of microbial therapy (probiotics) and microbiome manipulation in corals and answers to the need of having cnidarian model systems to test the function of bacteria and their effect on holobiont biology. Taken together, we provide import.

Citation
Costa, R. M., Cárdenas, A., Loussert-Fonta, C., Toullec, G., Meibom, A., & Voolstra, C. R. (2021). Surface Topography, Bacterial Carrying Capacity, and the Prospect of Microbiome Manipulation in the Sea Anemone Coral Model Aiptasia. Frontiers in Microbiology, 12. doi:10.3389/fmicb.2021.637834

Acknowledgements
We acknowledge the KAUST Imaging and Characterization Core Lab for their support in TEM and SEM analysis and the KAUST Bioscience Core Lab (BCL) for their support with the NGS data generation. We would like to thank all collaborators who tested the bacteria depletion protocol and provided feedback. We would also like to thank Carol Buitrago-Lopez and Hagen Gegner for their help with the coral collection and maintenance. Hydra magnipapillata and Nematostella vectensis were kindly provided by Prof. Takashi Gojobori’s group.

Publisher
Frontiers Media SA

Journal
Frontiers in Microbiology

DOI
10.3389/fmicb.2021.637834

Additional Links
https://www.frontiersin.org/articles/10.3389/fmicb.2021.637834/full

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