Successful coral microbiome transplant from high to low heat tolerant corals requires antibiotic pretreatment

Microbiome transplantation, used to treat human disease, can enhance thermal and pathogen resilience in bleaching-susceptible corals via coral microbiome transplantation (CMT), though success is donor- and recipient-dependent. In this study, less thermally tolerant Pachyseris speciosa fragments were exposed to ciprofloxacin or an antibiotic cocktail for 24 h, then received CMT from the thermally tolerant Acropora millepora from Singapore's turbid reef system. Alpha diversity increased only in antibiotic-treated, CMT fragments, demonstrating that antibiotic-induced dysbiosis enhanced bacterial uptake. Coral microbiome assemblage shifted significantly at 1 and 10 d, regardless of antibiotic treatment or Acropora inoculum. Antibiotic-induced dysbiosis did not enhance uptake of donor's core ASVs (e.g., Endozoicomonas spp.). However, early uptake favoured potential pathogens like Vibrio spp., while longer inoculation allowed for uptake of unculturable environmental taxa. Our approach of using antibiotic pretreatment followed by whole microbiome transplant parallels human faecal microbiota transplantation to restore gut health.