Rhodobacterales and Rhizobiales Are Associated With Stony Coral Tissue Loss Disease and Its Suspected Sources of Transmission

Abstract

In 2014, Stony Coral Tissue Loss Disease (SCTLD) was first detected off the coast of Miami, FL, United States, and continues to persist and spread along the Florida Reef Tractr (FRT) and into the Caribbean. SCTLD can have up to a 61% prevalence in reefs and has affected at least 23 species of scleractinian corals. This has contributed to the regional near-extinction of at least one coral species, Dendrogyra cylindrus. Initial studies of SCTLD indicate microbial community shifts and cessation of lesion progression in response to antibiotics on some colonies. However, the etiology and abiotic sources of SCTLD transmission are unknown. To characterize SCTLD microbial signatures, we collected tissue samples from four affected coral species: Stephanocoenia intersepta, Diploria labyrinthiformis, Dichocoenia stokesii, and Meandrina meandrites. Tissue samples were from apparently healthy (AH) corals, and unaffected tissue (DU) and lesion tissue (DL) on diseased corals. Samples were collected in June 2018 from three zones: (1) vulnerable (ahead of the SCTLD disease boundary in the Lower Florida Keys), (2) endemic (post-outbreak in the Upper Florida Keys), and (3) epidemic (SCTLD was active and prevalent in the Middle Florida Keys). From each zone, sediment and water samples were also collected to identify whether they may serve as potential sources of transmission for SCTLD-associated microbes. We used 16S rRNA gene amplicon highthroughput sequencing methods to characterize the microbiomes of the coral, water, and sediment samples. We identified a relatively higher abundance of the bacteria orders Rhodobacterales and Rhizobiales in DL tissue compared to AH and DU tissue. Also, our results showed relatively higher abundances of Rhodobacterales in water from the endemic and epidemic zones compared to the vulnerable zone. Rhodobacterales and Rhizobiales identified at higher relative abundances in DL samples were also detected in sediment samples, but not in water samples. Our data indicate that Rhodobacterales and Rhizobiales may play a role in SCTLD and that sediment may be a source of transmission for Rhodobacterales and Rhizobiales associated with SCTLD lesions.

Disease Diagnostics and Potential Coinfections by Vibrio coralliilyticus During an Ongoing Coral Disease Outbreak in Florida

“…Subsequently, various bacteria were identified that sometime elicited disease lesions when inoculated onto apparently healthy corals. These isolates belonged to the bacterial families Alteromonadaceae, Rhodobacteraceae, and Vibrionaceae, which, in a previous study, are families enriched for in SCTLD lesions (Meyer et al, 2019;Rosales et al, 2020). However, these isolates do not appear to be the primary cause of SCTLD as they do not consistently elicit disease during controlled experiments.…”

“…Additionally, microbial community analysis has identified various sequences belonging to the bacterial orders Flavobacteriales, Clostridiales, Rhodobacterales, Alteromonadales, and Vibrionales enriched at the disease lesions compared to the apparently heathy areas of the same colonies or healthy neighboring colonies (Meyer et al, 2019). A similar study identified sequences belonging to Rhodobacterales and Rhizobiales in disease tissue that matched those in the surrounding sediment, suggesting an environmental reservoir for at least some of these lesion-associated bacteria (Rosales et al, 2020). For both studies, the disease-associated sequences were not found in every disease lesion, and it is still unknown if a single etiological agent is responsible for SCTLD.…”

Effectiveness of topical antibiotics in treating corals affected by Stony Coral Tissue Loss Disease

“…However, efforts to identify the cause of the epidemic are ongoing and have identified differences in bacterial communities between healthy and diseased corals (Meyer et al, 2019;Rosales et al, 2020). Additionally, early laboratory work noted that water dosing with antibiotics resulted in disease cessation (O'Neil, Neely & Patterson, 2018;Aeby et al, 2019), suggesting a bacterial component.…”

Deciphering Coral Disease Dynamics: Integrating Host, Microbiome, and the Changing Environment

“…The pathobiont concept was developed based on evidence that gastrointestinal inflammatory diseases are often caused by bacterial species found in healthy hosts, including Clostridium difficile and Heliobacter pylori (Chow et al, 2011). Similarly, the Rhodobacteraceae increased fourfold in coral white syndrome lesions compared to healthy tissues (Pollock et al, 2017;Rosales et al, 2020) and are implicated in Stony Coral Tissue Loss Disease that is currently devastating Caribbean reefs. Therefore, it is possible that some coral diseases are caused by pathobionts rather than environmentally acquired pathogenic agents.…”