RESUMEN

Among the greatest threats to coral reefs are coral epizootics, which are increasing in frequency and severity across many reef ecosystems. In particular, white band disease (WBD) has devastated Caribbean acroporid populations since its initial outbreak in 1979. However, despite its widespread and damaging effects, the aetiology of WBD remains largely unresolved. Here, we examine the role of quorum sensing within bacterial communities associated with WBD-infected Acropora cervicornis. Microbial communities isolated from WBD-infected corals were exposed to quorum sensing inhibitor (QSI) - a N-acyl homoserine lactone autoinducer antagonist - and then dosed onto healthy test corals. WBD-associated bacteria supplemented with QSI lost the ability to establish disease, while healthy corals exposed to uninhibited WBD bacterial communities became infected within two days. Microbial 16S rRNA metagenomic sequencing analyses were then used to identify shifts in bacterial communities due to QSI exposure on WBD-associated bacterial communities. Our results demonstrated that Vibrionaceae and Flavobacteriaceae abundances were strongly inhibited by the addition of QSI to WBD-infected corals, whereas putative coral symbiont Endozoicomonas and Halomonadaceae abundances decrease dramatically in diseased corals.

Asunto(s)

RESUMEN

Coral diseases are a leading factor contributing to the global decline of coral reefs, and yet mechanisms of disease transmission remain poorly understood. This study tested whether zooplankton can act as a vector for white band disease (WBD) in Acropora cervicornis. Natural zooplankton communities were collected from a coral reef in Bocas del Toro, Panama. Half of the zooplankton were treated with antibiotics for 24 h after which the antibiotic-treated and non-antibiotic-treated zooplankton were incubated with either seawater or tissue homogenates from corals exhibiting WBD-like symptoms. A total of 15 of the 30 asymptomatic A. cervicornis colonies exposed to zooplankton incubated in disease homogenate in tank-based experiments showed signs of WBD, regardless of prior antibiotic incubation. These results indicate that in our experimental conditions zooplankton were a vector for coral disease after exposure to disease-causing pathogens. Given the importance of heterotrophy on zooplankton to coral nutrition, this potential mode of disease transmission warrants further investigation.

RESUMEN

Coral reefs have entered a state of global decline party due to an increasing incidence of coral disease. However, the diversity and complexity of coral-associated bacterial communities has made identifying the mechanisms underlying disease transmission and progression extremely difficult. This study explores the effects of coral cell-free culture fluid (CFCF) and autoinducer (a quorum sensing signaling molecule) on coral-associated bacterial growth and on coral tissue loss respectively. All experiments were conducted using the endangered Caribbean coral Acropora cervicornis. Coral-associated microbes were grown on selective media infused with CFCF derived from healthy and white band disease-infected A. cervicornis. Exposure to diseased CFCF increased proliferation of Cytophaga-Flavobacterium spp. while exposure to healthy CFCF inhibited growth of this group. Exposure to either CFCF did not significantly affect Vibrio spp. growth. In order to test whether disease symptoms can be induced in healthy corals, A. cervicornis was exposed to bacterial assemblages supplemented with exogenous, purified autoinducer. Incubation with autoinducer resulted in complete tissue loss in all corals tested in less than one week. These findings indicate that white band disease in A. cervicornis may be caused by opportunistic pathogenesis of resident microbes.

Asunto(s)