Antibiotics reduce bacterial load in Exaiptasia diaphana, but biofilms hinder its development as a gnotobiotic coral model

Abstract
Coral reefs are declining due to anthropogenic disturbances, including climate change. Therefore, improving our understanding of coral ecosystems is vital, and the influence of bacteria on coral health has attracted particular interest. However, a gnotobiotic coral model that could enhance studies of coral–bacteria interactions is absent. To address this gap, we tested the ability of treatment with seven antibiotics for 3 weeks to deplete bacteria in Exaiptasia diaphana, a sea anemone widely used as a coral model. Digital droplet PCR (ddPCR) targeting anemone Ef1-α and bacterial 16S rRNA genes was used to quantify bacterial load, which was found to decrease six-fold. However, metabarcoding of bacterial 16S rRNA genes showed that alpha and beta diversity of the anemone-associated bacterial communities increased significantly. Therefore, gnotobiotic E. diaphana with simplified, uniform bacterial communities were not generated, with biofilm formation in the culture vessels most likely impeding efforts to eliminate bacteria. Despite this outcome, our work will inform future efforts to create a much needed gnotobiotic coral model.

Citation
Hartman, L. M., Blackall, L. L., & van Oppen, M. J. H. (2022). Antibiotics reduce bacterial load in Exaiptasia diaphana, but biofilms hinder its development as a gnotobiotic coral model. Access Microbiology, 4(1). doi:10.1099/acmi.0.000314

Acknowledgements
The authors thank Dr Ruben Costa and Prof. Christian Voolstra from the King Abdullah University of Science and Technology (KAUST) for sharing a draft version of their gnotobiotic Aiptasia protocol. L.M.H. also thanks Ms Franca Casagranda from the University of Melbourne for her assistance in developing the ddPCR B/H assay.
This study was supported with funding from the Australian Research Council (grant ID: DP160101468) to M.v.O. and L.L.B. M.v.O acknowledges Australian Research Council Laureate Fellowship FL180100036.

Publisher
Microbiology Society

Journal
Access Microbiology

DOI
10.1099/acmi.0.000314

Additional Links
https://www.microbiologyresearch.org/content/journal/acmi/10.1099/acmi.0.000314

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