Biology subjects

Walker, B. K.

Publications and source records attributed to Walker, B. K..

4 recordsLinked to original sources

bioRxiv2025

Markers of resilience to stony coral tissue loss disease and probiotic potential in the microbiome of the threatened coral, Orbicella faveolata

Stony coral tissue loss disease (SCTLD) is widespread within the Caribbean and affects at least 22 species of reef-building coral. Bacteria have been implicated in the etiology of SCTLD, but the community of bacteria and archaea may also contribute to SCTLD resistance. To identify potential mechanisms through which microbes contribute to SCTLD resistance, we sequenced metagenomes from 41 colonies of the threatened coral, Orbicella faveolata, in the lower Florida Keys. All colonies were fate-tracked for three to five years and disease lesions were treated with amoxicillin. By 2024, 20% were never diseased, 10% had lesions before sampling but recovered, 22% were apparently healthy but were eventually susceptible to infection, and 49% had regular repeated infections. Within the coral microbiome, diseased and yet-to-be diseased colonies exhibited higher variability in functional genes. In contrast, corals that remained unaffected or recovered had less variable microbiomes with greater abundances of vitamin and antibiotic biosynthesis, secretion system, and quorum sensing genes that may support host health and resilience to pathogens. Though on some colonies antibiotic treatments were applied repeatedly, there was no effect on the diversity of beta-lactamases, antibiotic resistance genes that may confer amoxicillin resistance. Additional potentially probiotic gene clusters for the production of antimicrobial and bioactive compounds were present in many colonies regardless of fate. Taken together, we find significant probiotic potential in the coral microbiome to armor host O. faveolata corals against SCTLD infection, which may underpin intraspecific variation in stony coral tissue loss disease resilience and susceptibility.

microbiology↗

bioRxiv2025

Status of Florida's pillar coral population: in situ declines and ex situ successes

The population of the pillar coral, Dendrogyra cylindrus, in Florida was decimated from 2013-2020, primarily by the emergence of stony coral tissue loss disease (SCTLD). Monitoring of survivors from 2021 - early 2025 showed that the population underwent an additional 96% decline in live tissue, 78% loss in living colonies, and 57% loss of genotypes. SCTLD continued to be the primary cause of these losses. Though some surviving tissue isolates exhibited small amounts of growth, the population remains extremely small, with only an estimated 9.6 square meters of tissue remaining on 23 colonies (15 genotypes). Additionally, colonies are far too dispersed to successfully fertilize spawned gametes. The further declines in the population since 2020 highlight the instability of the remnant population, as well as the value of the pillar coral rescue program and ongoing propagation efforts. As of February 2025, eight different in situ and ex situ facilities were caring for rescued D. cylindrus. Experimental fragmentation at one in situ nursery identified variable, but continually increasing, growth rates across multiple fragmentation events. Sexual propagation efforts at an ex situ nursery documented 105 different rescue fragments spawning across five years. The smallest fragment was 9 x 7 x 9 cm, establishing a potential "minimum colony size" for reproductive capacity for this species. From these spawning events, 82 juveniles were being raised ex situ in early 2025. Two of these sexually propagated juveniles spawned six years after settlement, thus establishing a potential minimum age for reproduction.

ecology↗

bioRxiv2024

Metabolomic profiles of stony coral species from the Dry Tortugas National Park display inter- and intraspecies variation

Coral reefs are experiencing unprecedented loss in coral cover due to increased incidence of disease and bleaching events. Thus, understanding mechanisms of disease susceptibility and resilience, which vary by species, is important. In this regard, untargeted metabolomics serves as an important hypothesis-building tool enabling delineation of molecular factors underlying disease susceptibility or resilience. In this study, we characterize metabolomes of four species of visually healthy stony corals, including Meandrina meandrites, Orbicella faveolata, Colpophyllia natans, and Montastraea cavernosa, collected at least a year before stony coral tissue loss disease reached the Dry Tortugas, Florida and demonstrate that both symbiont and host-derived biochemical pathways vary by species. Metabolomes of Meandrina meandrites displayed minimal intraspecies variability and highest biological activity against coral pathogens when compared to other species in this study. Application of advanced metabolite annotation methods enabled delineation of several pathways underlying interspecies variability. Specifically, endosymbiont-derived vitamin E family compounds, betaine lipids, and host-derived acylcarnitines were among the top predictors of interspecies variability. Since several metabolite features that contributed to inter- and intraspecies variation are synthesized by the endosymbiotic Symbiodiniaceae, which could be a major source of these compounds in corals, our data will guide further investigations into these Symbiodiniaceae-derived pathways. Importance.Previous research profiling gene expression, proteins, and metabolites produced during thermal stress has reported the importance of endosymbiont-derived pathways in coral bleaching resistance. However, our understanding of interspecies variation in these pathways among healthy corals and their role in diseases is limited. We surveyed the metabolomes of four species of healthy corals with differing susceptibilities to the devastating stony coral tissue loss disease and applied advanced annotation approaches in untargeted metabolomics to determine the interspecies variation in host and endosymbiont-derived pathways. Using this approach, we propose the survey of immune markers such as vitamin E family compounds, acylcarnitines, and other metabolites to infer their role in resilience to coral diseases. As time-resolved multi-omics datasets are generated for disease-impacted corals, our approach and findings will be valuable in providing insight into the mechanisms of disease resistance.

systems biology↗

bioRxiv2021

Metabolomics of healthy and stony coral tissue loss disease affected Montastraea cavernosa corals

Stony coral tissue loss disease, first observed in Florida in 2014, has now spread along the entire Florida Reef Tract and on reefs in many Caribbean countries. The disease affects a variety of coral species with differential outcomes, and in many instances results in whole-colony mortality. We employed untargeted metabolomic profiling of Montastraea cavernosa corals affected by stony coral tissue loss disease to identify metabolic markers of disease. Herein, extracts from apparently healthy, diseased, and recovered corals, Montastraea cavernosa, collected at a reef site near Ft. Lauderdale, Florida were subjected to liquid-chromatography mass spectrometry-based metabolomics. Unsupervised principal component analysis reveals wide variation in metabolomic profiles of healthy corals of the same species, which differ from diseased corals. Using a combination of supervised and unsupervised data analyses tools, we describe metabolite features that explain variation between the apparently healthy corals, between diseased corals, and between the healthy and the diseased corals. By employing a culture-based approach, we assign sources of a subset of these molecules to the endosymbiotic dinoflagellates, Symbiodiniaceae. Specifically, we identify various endosymbiont-specific lipid classes, such as betaine lipids, glycolipids, and tocopherols, which differentiate samples taken from apparently healthy corals and diseased corals. Given the variation observed in metabolite fingerprints of corals, our data suggests that metabolomics is a viable approach to link metabolite profiles of different coral species with their susceptibility and resilience to numerous coral diseases spreading through reefs worldwide.

systems biology↗