Abstract
Australian Subtropical White Syndrome (ASWS) is an infectious, temperature dependent disease of the subtropical coral Turbinaria mesenterina involving a hitherto unknown transmissible causative agent. This report describes significant changes in the coral associated bacterial community as the disease progresses from the apparently healthy tissue of ASWS affected coral colonies, to areas of the colony affected by ASWS lesions, to the dead coral skeleton exposed by ASWS. In an effort to better understand the potential roles of bacteria in the formation of disease lesions, the effect of antibacterials on the rate of lesion progression was tested, and both culture based and culture independent techniques were used to investigate the bacterial communities associated with colonies of T. mesenterina. Culture-independent analysis was performed using the Oligonucleotide Fingerprinting of Ribosomal Genes (OFRG) technique, which allowed a library of 8094 cloned bacterial 16S ribosomal genes to be analysed. Interestingly, the bacterial communities associated with both healthy and disease affected corals were very diverse and ASWS associated communities were not characterized by a single dominant organism. Treatment with antibacterials had a significant effect on the rate of progress of disease lesions (p = 0.006), suggesting that bacteria may play direct roles as the causative agents of ASWS. A number of potential aetiological agents of ASWS were identified in both the culture-based and culture-independent studies. In the culture-independent study an Alphaproteobacterium closely related to Roseovarius crassostreae, the apparent aetiological agent of juvenile oyster disease, was found to be significantly associated with disease lesions. In the culture-based study Vibrio harveyi was consistently associated with ASWS affected coral colonies and was not isolated from any healthy colonies. The differing results of the culture based and culture-independent studies highlight the importance of using both approaches in the investigation of microbial communities.
Highlights
The incidence of diseases of scleractinian corals and other reef organisms has increased over the past 20 years, resulting in drastic changes to some reef ecosystems, including total loss of coral cover in some locations [1,2]
Turbinaria mesenterina is an ecologically important scleractinian coral that is abundant on shallow rocky reefs in subtropical eastern Australia, where it comprises a large proportion of the benthic cover [7,8]
Four serial dilutions of 1021 to 1024 of the resulting slurry were prepared in sterile filtered seawater (FSW). 10 mL aliquots of syringe samples were diluted with sterile FSW. 100 ml aliquots of each dilution were spread on agar plates containing a non-selective marine heterotrophic growth medium (Salt Luria Broth SLB agar [32]), which were incubated at 30uC for up to five days. 30uC was chosen as the incubation temperature for bacterial cultures because this temperature resulted in relatively rapid growth of most bacterial strains, and the aim of this work was to isolate as many strains as possible as quickly as possible
Summary
The incidence of diseases of scleractinian (reef building) corals and other reef organisms has increased over the past 20 years, resulting in drastic changes to some reef ecosystems, including total loss of coral cover in some locations [1,2]. In 2000, a newly observed syndrome was reported affecting T. mesenterina and other coral species in the Solitary Islands Marine Park (SIMP), NSW, Australia. This syndrome presents as a typical ‘white syndrome’ with gradual loss of living tissue which may begin at any point on the coral colony as a small patch of missing tissue, before spreading outwards, forming a lesion of exposed white skeleton [9]. Dalton et al [10] used field and aquarium experiments to demonstrate that the syndrome is a temperature-dependant, infectious disease, which can be transmitted by direct contact between coral colonies, and possibly via a predatory vector [11]
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