School of BioSciences - Research Publications
Permanent URI for this collection
Search Results
1 - 10 of 13
-
ItemFluorescence lifetime imaging microscopy (FLIM): a non-traditional approach to study host-microbial symbioses(CSIRO PUBLISHING, 2022)Corals and their photosynthetic endosymbiotic algae (Symbiodiniaceae) produce a strong autofluorescent signal that spans the visible to near-infrared (NIR) spectrum. However, this broad-spectrum emission hinders the use of fluorescence in situ hybridisation (FISH) for the study of bacterial heterogeneity within the different niches of corals and Symbiodiniaceae, because FISH fluorophores also fluoresce within the visible to NIR spectrum. A solution to this impediment is to use fluorescence lifetime imaging microscopy (FLIM). The ‘lifetime’ property of fluorophores is a feature that enables sample (e.g. coral/Symbiodiniaceae) autofluorescence to be distinguished from FISH-labelled bacteria. In this manner, the location of bacteria around and within Symbiodiniaceae can be quantified along with their identity and spatial distribution. Furthermore, the ‘lifetime’ of the host and associated microbe cellular autofluorescence can be analysed in terms of endogenous fluorophore composition (e.g. metabolic co-factors, aromatic amino acids) and serves as information for symbiotic versus parasitic host-microbe association.
-
ItemExploring microbiome engineering as a strategy for improved thermal tolerance in Exaiptasia diaphana(OXFORD UNIV PRESS, 2022-04)AIMS: Fourteen percent of all living coral, equivalent to more than all the coral on the Great Barrier Reef, has died in the past decade as a result of climate change-driven bleaching. Inspired by the 'oxidative stress theory of coral bleaching', we investigated whether a bacterial consortium designed to scavenge free radicals could integrate into the host microbiome and improve thermal tolerance of the coral model, Exaiptasia diaphana. METHODS AND RESULTS: E. diaphana anemones were inoculated with a consortium of high free radical scavenging (FRS) bacteria, a consortium of congeneric low FRS bacteria, or sterile seawater as a control, then exposed to elevated temperature. Increases in the relative abundance of Labrenzia during the first 2 weeks following the last inoculation provided evidence for temporary inoculum integration into the E. diaphana microbiome. Initial uptake of other consortium members was inconsistent, and these bacteria did not persist either in E. diaphana's microbiome over time. Given their non-integration into the host microbiome, the ability of the FRS consortium to mitigate thermal stress could not be assessed. Importantly, there were no physiological impacts (negative or positive) of the bacterial inoculations on the holobiont. CONCLUSIONS: The introduced bacteria were not maintained in the anemone microbiome over time, thus, their protective effect is unknown. Achieving long-term integration of bacteria into cnidarian microbiomes remains a research priority. SIGNIFICANCE AND IMPACT OF THE STUDY: Microbiome engineering strategies to mitigate coral bleaching may assist coral reefs in their persistence until climate change has been curbed. This study provides insights that will inform microbiome manipulation approaches in coral bleaching mitigation research.
-
ItemLack of evidence for the oxidative stress theory of bleaching in the sea anemone, Exaiptasia diaphana, under elevated temperature(SPRINGER, 2022-08)Abstract To survive in nutrient-poor waters corals rely on a symbiotic association with intracellular microalgae. However, increased sea temperatures cause algal loss—known as coral bleaching—often followed by coral death. Some of the most compelling evidence in support of the ‘oxidative stress theory of coral bleaching’ comes from studies that exposed corals, cultures of their algal endosymbionts, or the coral modelExaiptasia diaphanato exogenous antioxidants during thermal stress. Here, we replicate these experiments usingE.diaphanawith the addition of the antioxidants ascorbate + catalase, catechin, or mannitol under ambient and elevated temperatures along with an antioxidant-free control. In the absence of exogenous antioxidants,E.diaphanaexposed to elevated temperatures bleached with no change in reactive oxygen species (ROS) levels associated with their microalgal cells. Ascorbate + catalase and mannitol treatments rescued the anemones from bleaching, although microalgal ROS levels increased in these antioxidant treatments under elevated temperature conditions. While bleaching was not associated with changes in net ROS for the intracellular algal symbionts, it is evident from our findings that excess ROS is connected to the bleaching phenotype as exogenous antioxidants were successful in mitigating the effects of thermal stress in cnidarians. This understanding may assist applied research that aims to reduce the impact of climate change on coral reefs.
-
ItemAntibiotics reduce bacterial load in Exaiptasia diaphana, but biofilms hinder its development as a gnotobiotic coral model.(Microbiology Society, 2022)Coral reefs are declining due to anthropogenic disturbances, including climate change. Therefore, improving our understanding of coral ecosystems is vital, and the influence of bacteria on coral health has attracted particular interest. However, a gnotobiotic coral model that could enhance studies of coral-bacteria interactions is absent. To address this gap, we tested the ability of treatment with seven antibiotics for 3 weeks to deplete bacteria in Exaiptasia diaphana, a sea anemone widely used as a coral model. Digital droplet PCR (ddPCR) targeting anemone Ef1-α and bacterial 16S rRNA genes was used to quantify bacterial load, which was found to decrease six-fold. However, metabarcoding of bacterial 16S rRNA genes showed that alpha and beta diversity of the anemone-associated bacterial communities increased significantly. Therefore, gnotobiotic E. diaphana with simplified, uniform bacterial communities were not generated, with biofilm formation in the culture vessels most likely impeding efforts to eliminate bacteria. Despite this outcome, our work will inform future efforts to create a much needed gnotobiotic coral model.
-
ItemIntracellular Bacterial Symbionts in Corals: Challenges and Future Directions(MDPI, 2021-11)Corals are the main primary producers of coral reefs and build the three-dimensional reef structure that provides habitat to more than 25% of all marine eukaryotes. They harbor a complex consortium of microorganisms, including bacteria, archaea, fungi, viruses, and protists, which they rely on for their survival. The symbiosis between corals and bacteria is poorly studied, and their symbiotic relationships with intracellular bacteria are only just beginning to be acknowledged. In this review, we emphasize the importance of characterizing intracellular bacteria associated with corals and explore how successful approaches used to study such microorganisms in other systems could be adapted for research on corals. We propose a framework for the description, identification, and functional characterization of coral-associated intracellular bacterial symbionts. Finally, we highlight the possible value of intracellular bacteria in microbiome manipulation and mitigating coral bleaching.
-
ItemDevelopment of a free radical scavenging bacterial consortium to mitigate oxidative stress in cnidarians(WILEY, 2021-09)Corals are colonized by symbiotic microorganisms that profoundly influence the animal's health. One noted symbiont is a single-celled alga (in the dinoflagellate family Symbiodiniaceae), which provides the coral with most of its fixed carbon. Thermal stress increases the production of reactive oxygen species (ROS) by Symbiodiniaceae during photosynthesis. ROS can both damage the algal symbiont's photosynthetic machinery and inhibit its repair, causing a positive feedback loop for the toxic accumulation of ROS. If not scavenged by the antioxidant network, excess ROS may trigger a signaling cascade ending with the coral host and algal symbiont disassociating in a process known as bleaching. We use Exaiptasia diaphana as a model for corals and constructed a consortium comprised of E. diaphana-associated bacteria capable of neutralizing ROS. We identified six strains with high free radical scavenging (FRS) ability belonging to the families Alteromonadaceae, Rhodobacteraceae, Flavobacteriaceae and Micrococcaceae. In parallel, we established a consortium of low FRS isolates consisting of genetically related strains. Bacterial whole genome sequences were used to identify key pathways that are known to influence ROS.
-
ItemMixed-mode bacterial transmission in the common brooding coral Pocillopora acuta(WILEY, 2020-01)Reef-building corals form associations with a huge diversity of microorganisms, which are essential for the survival and well-being of their host. While the acquisition patterns of Symbiodiniaceae microalgal endosymbionts are strongly linked to the coral's reproductive strategy, few studies have investigated the transmission mode of bacteria, especially in brooding species. Here, we relied on 16S rRNA gene and Internal Transcribed Spacer 2 marker metabarcoding in conjunction with fluorescence in situ hybridisation microscopy to describe the onset of microbial associations in the common brooding coral Pocillopora acuta. We analysed the bacterial and Symbiodiniaceae community composition in five adult colonies, their larvae, and 4-day old recruits. Larvae and recruits inherited Symbiodiniaceae, as well as a small number of bacterial strains, from their parents. Rhodobacteraceae and Endozoicomonas were among the most abundant taxa that were likely maternally transmitted to the offspring. The presence of bacterial aggregates in newly released larvae was observed with confocal microscopy, confirming the occurrence of vertical transmission of bacteria in P. acuta. We concluded that host factors, as well as the environmental bacterial pool influenced the microbiome of P. acuta.
-
ItemMicrobiome characterization of defensive tissues in the model anemone Exaiptasia diaphana(BMC, 2021-05-21)BACKGROUND: Coral reefs are among the most diverse and productive ecosystems on Earth. This success relies on the coral's association with a wide range of microorganisms, including dinoflagellates of the family Symbiodiniaceae that provide coral hosts with most of their organic carbon requirements. While bacterial associates have long been overlooked, research on these microorganisms is gaining traction, and deciphering bacterial identity and function is greatly enhancing our understanding of cnidarian biology. Here, we investigated bacterial communities in defensive tissues (acontia) of the coral model, the sea anemone Exaiptasia diaphana. Acontia are internal filaments that are ejected upon detection of an external threat and release toxins to repel predators. RESULTS: Using culturing techniques and 16S rRNA gene metabarcoding we identified bacterial communities associated with acontia of four Great Barrier Reef-sourced E. diaphana genotypes. We show that bacterial communities are similar across genotypes, and dominated by Alteromonadaceae, Vibrionaceae, Rhodobacteraceae, and Saprospiraceae. By analyzing abundant amplicon sequence variants (ASVs) from metabarcoding data from acontia and comparing these to data from whole anemones, we identified five potentially important bacterial genera of the acontia microbiome: Vibrio, Sulfitobacter, Marivita, Alteromonas, and Lewinella. The role of these bacteria within the acontia remains uninvestigated but could entail assistance in defense processes such as toxin production. CONCLUSIONS: This study provides insight into potential bacterial involvement in cnidarian defense tissues and highlights the need to study bacterial communities in individual compartments within a holobiont.
-
ItemMicrobiota characterization of Exaiptasia diaphana from the Great Barrier Reef.(bmc springer nature, 2020-04-05)BACKGROUND: Coral reefs have sustained damage of increasing scale and frequency due to climate change, thereby intensifying the need to elucidate corals' biological characteristics, including their thermal tolerance and microbial symbioses. The sea anemone, Exaiptasia diaphana, has proven an ideal coral model for many studies due to its close phylogenetic relationship and shared traits, such as symbiosis with algae of the family Symbiodiniaceae. However, established E. diaphana clonal lines are not available in Australia thus limiting the ability of Australian scientists to conduct research with this model. To help address this, the bacterial and Symbiodiniaceae associates of four Great Barrier Reef (GBR)-sourced E. diaphana genotypes established in laboratory aquaria and designated AIMS1-4, and from proxies of wild GBR E. diaphana were identified by metabarcoding of the bacterial 16S rRNA gene and eukaryotic rRNA gene ITS2 region. The relationship between AIMS1-4 and their bacterial associates was investigated, as was bacterial community phenotypic potential. Existing data from two existing anemone clonal lines, CC7 and H2, were included for comparison. RESULTS: Overall, 2238 bacterial amplicon sequence variants (ASVs) were observed in the AIMS1-4 bacterial communities, which were dominated by Proteobacteria and Bacteroidetes, together comprising > 90% relative abundance. Although many low abundance bacterial taxa varied between the anemone genotypes, the AIMS1-4 communities did not differ significantly. A significant tank effect was identified, indicating an environmental effect on the microbial communities. Bacterial community richness was lower in all lab-maintained E. diaphana compared to the wild proxies, suggesting a reduction in bacterial diversity and community phenotypic potential due to culturing. Seventeen ASVs were common to every GBR lab-cultured anemone, however five were associated with the Artemia feedstock, making their specific association to E. diaphana uncertain. The dominant Symbiodiniaceae symbiont in all GBR anemones was Breviolum minutum. CONCLUSION: Despite differences in the presence and abundance of low abundance taxa, the bacterial communities of GBR-sourced lab-cultured E. diaphana are generally uniform and comparable to communities reported for other lab-cultured E. diaphana. The data presented here add to the global E. diaphana knowledge base and make an important contribution to the establishment of a GBR-sourced coral model organism.
-
ItemIntracellular bacteria are common and taxonomically diverse in cultured and in hospite algal endosymbionts of coral reefs(SPRINGERNATURE, 2021-07)Corals house a variety of microorganisms which they depend on for their survival, including endosymbiotic dinoflagellates (Symbiodiniaceae) and bacteria. While cnidarian-microorganism interactions are widely studied, Symbiodiniaceae-bacteria interactions are only just beginning to receive attention. Here, we describe the localization and composition of the bacterial communities associated with cultures of 11 Symbiodiniaceae strains from nine species and six genera. Three-dimensional confocal laser scanning and electron microscopy revealed bacteria are present inside the Symbiodiniaceae cells as well as closely associated with their external cell surface. Bacterial pure cultures and 16S rRNA gene metabarcoding from Symbiodiniaceae cultures highlighted distinct and highly diverse bacterial communities occur intracellularly, closely associated with the Symbiodiniaceae outer cell surface and loosely associated (i.e., in the surrounding culture media). The intracellular bacteria are highly conserved across Symbiodiniaceae species, suggesting they may be involved in Symbiodiniaceae physiology. Our findings provide unique new insights into the biology of Symbiodiniaceae.