Stony coral tissue loss disease intervention with amoxicillin leads to a reversal of disease‐modulated gene expression pathways

Abstract

Stony coral tissue loss disease (SCTLD) remains an unprecedented disease outbreak due to its high mortality rate and rapid spread throughout Florida's Coral Reef and wider Caribbean. A collaborative effort is underway to evaluate strategies that mitigate the spread of SCTLD across coral colonies and reefs, including restoration of disease‐resistant genotypes, genetic rescue, and disease intervention with therapeutics. We conducted an in‐situ experiment in Southeast Florida to assess molecular responses among SCTLD‐affected Montastraea cavernosa pre‐ and post‐application of the most widely used intervention method, CoreRx Base 2B with amoxicillin. Through Tag‐Seq gene expression profiling of apparently healthy, diseased, and treated corals, we identified modulation of metabolomic and immune gene pathways following antibiotic treatment. In a complementary ex‐situ disease challenge experiment, we exposed nursery‐cultured M. cavernosa and Orbicella faveolata fragments to SCTLD‐affected donor corals to compare transcriptomic profiles among clonal individuals from unexposed controls, those exposed and displaying disease signs, and corals exposed and not displaying disease signs. Suppression of metabolic functional groups and activation of stress gene pathways as a result of SCTLD exposure were apparent in both species. Amoxicillin treatment led to a ‘reversal’ of the majority of gene pathways implicated in disease response, suggesting potential recovery of corals following antibiotic application. In addition to increasing our understanding of molecular responses to SCTLD, we provide resource managers with transcriptomic evidence that disease intervention with antibiotics appears to be successful and may help to modulate coral immune responses to SCTLD. These results contribute to feasibility assessments of intervention efforts following disease outbreaks and improved predictions of coral reef health across the wider Caribbean.

Stony coral tissue loss disease: a review of emergence, impacts, etiology, diagnostics, and intervention

“…The family is comprised of seven genera: Symbiodinium (formerly clade A), Breviolum (formerly clade B), Cladocopium (formerly clade C), Durusdinium (formerly clade D), Effrenium (formerly clade E), Fugacium (formerly clade F), and Gerakladium (formerly clade G), each comprised of species and subspecies (Baker, 2003;LaJeunesse and Thornhill, 2011;LaJeunesse et al, 2018;Davies et al, 2023), though Caribbean corals typically only associate with Symbiodinium, Breviolum, Cladocopium, and Durusdinium (Baker, 2003;Van Oppen and Burghardt, 2009). Field observations, histopathology, and laboratory-based and molecular-based studies provide strong evidence of coral-Symbiodiniaceae dysbiosis in response to SCTLD (Landsberg et al, 2020;Deutsch et al, 2021;Meiling et al, 2021;Work et al, 2021;Studivan et al, 2022b;Williamson et al, 2022;Beavers et al, 2023;Studivan et al, 2023).…”

“…Treatment experiments in the British Virgin Islands had a positive effect on the coral community compared to untreated reefs (Forrester et al, 2022), suggesting that treatment might slow the spread of SCTLD across a reef (Neely et al, 2021c;Forrester et al, 2022). Transcriptomic analysis likewise demonstrated that amoxicillin treatments resulted in the reversal of gene expression pathways to a pre-diseased state, possibly benefiting the coral immune response (Studivan et al, 2023).…”

Novel metagenomics analysis of stony coral tissue loss disease

“…Multiple studies have explored viruses that may infect stony coral symbionts, notably Symbiodiniaceae, but no causative relationships have been detected (Work et al 2021;Veglia et al 2022;Beavers et al 2023;Howe-Kerr et al 2023). Bacterial species are particularly under scrutiny for their potential involvement in SCTLD, due to the effectiveness of antibiotics in halting lesion progression in multiple affected coral species (Aeby et al 2019, Neely et al 2020Shilling et al 2021;Studivan et al 2023). Consequently, SCTLD studies have predominantly focused on understanding changes in the bacterial community between apparently healthy and SCTLDaffected corals.…”