Evaluating the Effect of Amoxicillin Treatment on the Microbiome of Orbicella faveolata with Caribbean Yellow Band Disease

Host microbiomes play a key role in coral disease dynamics, thus it is essential to characterize microbial communities of diseased tissues and identify how they are altered by potential treatments, especially as coral reefs continue to decline globally. The abundance of Orbicella faveolata, a major reef-building Caribbean coral species, has significantly declined due to several stressors including infectious disease. Caribbean yellow band disease (CYBD) often results in complete colony mortality. We applied an amoxicillin-laced Base2B ointment to CYBD lesion areas on O. faveolata within Buck Island Reef National Monument, St. Croix, USVI, trying to halt disease progression. Another CYBD lesion area on the same colony served as a paired untreated control. Microbiomes of the apparently healthy tissue adjacent to the treatment were characterized pre-treatment and two days post-treatment, along with the paired untreated CYBD controls and nearby healthy colonies. Both microbiomes of untreated CYBD lesions and apparently healthy tissue on CYBD colonies had significantly higher alpha diversity and significantly differed from those of nearby healthy colonies, suggesting potential systemic effects of CYBD. Amoxicillin treatment significantly changed the microbial community composition of tissue adjacent to the treatment. The bacterial family Vibrionaceae, a putative pathogen for CYBD and often associated with other coral diseases, was enriched post-treatment. However, the lesion progression rates of treated and untreated lesion areas were similar. Our results suggest that amoxicillin may disrupt the microbiome of adjacent tissue on O. faveolata, allowing for opportunistic Vibrio sp. bacteria to colonize and may not be an effective treatment for CYBD.