Biology subjects

Dungan, A. M.

Publications and source records attributed to Dungan, A. M..

6 recordsLinked to original sources

bioRxiv2025

Genomic prediction of symbiotic interactions between two Endozoicomonas clades and their coral host, Acropora loripes

BackgroundThe bacterial genus Endozoicomonas is a predominant member of the coral microbiome, widely recognised for its ubiquity and ability to form high-density aggregates within coral tissues. Hence, investigating its metabolic interplay with coral hosts offers critical insights into its ecological roles and contributions to coral health and resilience. ResultsUsing long- and short-read whole-genome sequencing of 11 Endozoicomonas strains from Acropora loripes, genome sizes were found to range between 5.8 and 7.1 Mbp. Phylogenomic analysis identified two distinct clades within the family Endozoicomonadaceae. Metabolic reconstruction uncovered clade-specific pathways, including the degradation of holobiont-derived carbon and lipids (e.g., galactose, starch, triacylglycerol, D-glucuronate), latter of suggest involvement of Endozoicomonas in host sex-type steroid hormone metabolism. A clade-specific type 6 Secretion System (T6SS) and predicted effector molecules were identified, potentially facilitating coral-bacterium symbiosis. Additionally, genomic analyses revealed diverse phosphorus acquisition strategies, implicating Endozoicomonas in holobiont phosphorus cycling and stress responses. ConclusionsThis study reveals clade-specific genomic signatures of Endozoicomonas supporting its mutualistic lifestyle within corals. Findings suggests possible roles in nutrient cycling, reproductive health, and stress resilience, offering novel insights into coral holobiont functioning and potential strategies for reef restoration.

genomics↗

bioRxiv2024

Differential aggregation patterns of Endozoicomonas within tissues of the coral Acropora loripes

Bacteria in the genus Endozoicomonas are well-known coral symbionts commonly found as clusters within tissues of several coral species. Mapping the spatial distribution of these microbial communities is critical to gaining a holistic understanding of the potential role they may play within the coral host. This study focuses on characterising bacterial aggregates associated with the common reef-building coral, Acropora loripes, from the central Great Barrier Reef, Australia. A conventional cultivation-based method was employed to establish a pure culture collection of 11 undescribed Endozoicomonas strains isolated from A. loripes. Subsequent 16S rRNA gene sequence analysis revealed their classification into two distinct phylogenetic clades. To resolve their spatial distribution in hospite, clade-specific fluorescence in situ hybridisation probes were designed. Aggregates were consistently observed in the gastrodermal tissue layers surrounding the upper and lower gastrovascular cavity and were predominantly formed by cells from the same phylogenetic clade, with a minor proportion of aggregates formed by Endozoicomonas from both targeted clades. Furthermore, a clear distinction in aggregation pattern was observed; one clade exhibited clusters with regular and contained growth patterns, whereas the other formed clusters lacking clear boundaries and having irregular shapes. Scanning electron microscopy revealed the presence of a membrane of unknown origin associated with bacterial aggregates in two instances, suggesting potential structural or functional differences in these aggregates. These contrasting morphological features underscore the need for comprehensive investigations into the underlying mechanisms governing bacterial aggregate formation in corals.

ecology↗

bioRxiv2023

Fecal bacterial communities of the platypus (Ornithorhynchus anatinus) reflect captivity status: implications for conservation and management

The duck-billed platypus (Ornithorhynchus anatinus) is currently listed as Near-Threatened under the International Union for Conservation of Nature (IUCN) Red List based on observed population declines and local extinctions. A key part of the conservation strategy for this species is its captive maintenance; however, captive animals often undergo significant changes in their gut microbiome. The study of the gut microbiome in threatened wildlife species has enormous potential to improve conservation efforts and gain insights into host-microbe coevolution. Here, for the first time, we characterize the gut microbiome of wild platypus via fecal samples using high-throughput sequencing of the bacterial 16S rRNA gene and identify microbial biomarkers of captivity in this species. At the phylum level, Firmicutes (50.4%) predominated among all platypuses, followed by Proteobacteria (28.7%), Fusobacteria (13.4%), and Bacteroidota (6.9%), with twenty-one core bacteria identified. Captive individuals did not differ in their microbial -diversity compared to wild platypus but had significantly different community composition ({beta}-diversity) and exhibited higher abundances of Enterococcus, which are potential pathogenic bacteria. Four taxa were identified as biomarkers of wild platypus, including Rickettsiella, Epulopiscium, Clostridium, and Cetobacterium. This contrast in gut microbiome composition between wild and captive platypus is an essential insight for guiding conservation management as the rewilding of captive animal microbiomes is a new and emerging tool to improve captive animal health, maximize captive breeding efforts, and give reintroduced or translocated animals the best chance of survival.

microbiology↗

bioRxiv2023

DNA from non-viable bacteria biases diversity estimates in the corals Acropora loripes and Pocillopora acuta

BackgroundNucleic acid-based analytical methods have greatly expanded our understanding of global prokaryotic diversity, yet standard metabarcoding methods provide no information on the most fundamental physiological state of bacteria, viability. Scleractinian corals harbour a complex microbiome in which bacterial symbionts play critical roles in maintaining health and functioning of the holobiont. However, the coral holobiont contains both dead and living bacteria. The former can be the result of corals feeding on bacteria, rapid swings from hyper- to hypoxic conditions in the coral tissue, the presence of antimicrobial compounds in coral mucus, and an abundance of lytic bacteriophages. ResultsBy combining propidium monoazide (PMA) treatment with high-throughput sequencing on six coral species (Acropora loripes, A. millepora, A. kenti, Platygyra daedalea, Pocillopora acuta, and Porites lutea) we were able to obtain information on bacterial communities with little noise from non-viable microbial DNA. Metabarcoding of the 16S rRNA gene showed significantly higher community evenness (85%) and species diversity (31%) in untreated compared with PMA-treated tissue for A. loripes only. While PMA-treated coral did not differ significantly from untreated samples in terms of observed number of ASVs, >30% of ASVs were identified in untreated samples only, suggesting that they originated from cell-free/non-viable DNA. Further, the bacterial community structure was significantly different between PMA-treated and untreated samples for A. loripes and P. acuta indicating that DNA from non-viable microbes can bias community composition data in coral species with low bacterial diversity. ConclusionsOur study is highly relevant to microbiome studies on coral and other host organisms as it delivers a solution to excluding non-viable DNA in a complex community. These results provide novel insights into the dynamic nature of host-associated microbiomes and underline the importance of applying versatile tools in the analysis of metabarcoding or next-generation sequencing data sets.

microbiology↗

bioRxiv2020

Development of a free radical scavenging probiotic to mitigate coral bleaching

Corals are colonized by symbiotic microorganisms that exert a profound influence on the animals health. One noted symbiont is a single-celled alga (from the family Symbiodiniaceae), which provides the coral with most of its fixed carbon. During thermal stress, hyperactivity of photosynthesis results in a toxic accumulation of reactive oxygen species (ROS). If not scavenged by the antioxidant network, ROS may trigger a signaling cascade ending with the coral host and algal symbiont disassociating; this process is known as bleaching. Our goal was to construct a probiotic comprised of host-associated bacteria able to neutralize free radicals such as ROS. Using the coral model, the anemone Exaiptasia diaphana, and pure bacterial cultures isolated from the model animal, we identified six strains with high free radical scavenging ability belonging to the families Alteromonadaceae, Rhodobacteraceae, Flavobacteriaceae, and Micrococcaceae. In parallel, we established a "negative" probiotic consisting of genetically related strains with poor free radical scavenging capacities. From their whole genome sequences, we explored genes of interest that may contribute to their potential beneficial roles, which may help facilitate the therapeutic application of a bacterial probiotic. In particular, the occurrence of key pathways that are known to influence ROS in each of the strains has been inferred from the genomes sequences and are reported here. IMPORTANCECoral bleaching is tightly linked to the production of reactive oxygen species (ROS), which accumulates to a toxic level in algae-harboring host cells leading to coral-algal dissociation. Interventions targeting ROS accumulation, such as the application of exogenous antioxidants, have shown promise for maintaining the coral-algal partnership. With the feasibility of administering antioxidants directly to corals being low, we aim to develop a probiotic to neutralize toxic ROS during a thermal stress event. This probiotic can be tested with corals or a coral model to assess its efficacy in improving coral resistance to environmental stress.

bioengineering↗

bioRxiv2019

Exaiptasia diaphana from the Great Barrier Reef: a valuable resource for coral symbiosis research

The sea anemone, Exaiptasia diaphana, commonly known as Exaiptasia pallida or Aiptasia pallida, has become increasingly popular as a model for cnidarian-microbiome symbiosis studies due to its relatively rapid growth, ability to reproduce sexually and asexually, and symbiosis with diverse prokaryotes and the same microalgal symbionts (family Symbiodiniaceae) as its coral relatives. Clonal E. diaphana strains from Hawaii, the Atlantic Ocean, and Red Sea are now established for use in research. Here, we introduce Great Barrier Reef (GBR)-sourced E. diaphana strains as additions to the model repertoire. Sequencing of the 18S rRNA gene confirmed the anemones to be E. diaphana while genome-wide single nucleotide polymorphism analysis revealed four distinct genotypes. Based on Exaiptasia-specific inter-simple sequence repeat (ISSR)-derived sequence characterized amplified region (SCAR) marker and gene loci data, these four E. diaphana genotypes are distributed across several divergent phylogenetic clades with no clear phylogeographical pattern. The GBR E. diaphana genotypes comprised three females and one male, which all host Breviolum minutum as their homologous Symbiodiniaceae endosymbiont. When acclimating to an increase in light levels from 12 to 28 mol photons m-2 s-1, the genotypes exhibited significant variation in maximum quantum yield of Symbiodiniaceae photosystem II and Symbiodiniaceae cell density. The comparatively high levels of physiological and genetic variability among GBR anemone genotypes makes these animals representative of global E. diaphana diversity and thus excellent model organisms. The addition of these GBR strains to the worldwide E. diaphana collection will contribute to cnidarian symbiosis research, particularly in relation to the climate resilience of coral reefs.

zoology↗