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Webb RJ, Roberts AA, Rush C, Skerratt LF, Tizard ML, Berger L. Small Interfering RNA Mediated Messenger RNA Knockdown in the Amphibian Pathogen Batrachochytrium dendrobatidis. J Basic Microbiol 2024; 64:e2400081. [PMID: 39031701 DOI: 10.1002/jobm.202400081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 05/03/2024] [Accepted: 05/19/2024] [Indexed: 07/22/2024]
Abstract
RNA interference (RNAi) has not been tested in the pandemic amphibian pathogen, Batrachochytrium dendrobatidis, but developing this technology could be useful to elucidate virulence mechanisms, identify therapeutic targets, and may present a novel antifungal treatment option for chytridiomycosis. To manipulate and decipher gene function, rationally designed small interfering RNA (siRNA) can initiate the destruction of homologous messenger RNA (mRNA), resulting in the "knockdown" of target gene expression. Here, we investigate whether siRNA can be used to manipulate gene expression in B. dendrobatidis via RNAi using differing siRNA strategies to target genes involved in glutathione and ornithine synthesis. To determine the extent and duration of mRNA knockdown, target mRNA levels were monitored for 24-48 h after delivery of siRNA targeting glutamate-cysteine ligase, with a maximum of ~56% reduction in target transcripts occurring at 36 h. A second siRNA design targeting glutamate-cysteine ligase also resulted in ~53% knockdown at this time point. siRNA directed toward a different gene target, ornithine decarboxylase, achieved 17% reduction in target transcripts. Although no phenotypic effects were observed, these results suggest that RNAi is possible in B. dendrobatidis, and that gene expression can be manipulated in this pathogen. We outline ideas for further optimization steps to increase knockdown efficiency to better harness RNAi techniques for control of B. dendrobatidis.
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Affiliation(s)
- Rebecca J Webb
- One Health Research Group, Melbourne Veterinary School, University of Melbourne, Werribee, Victoria, Australia
- Australian Institute of Tropical Health and Medicine, James Cook Univiersity, Townsville, Queensland, Australia
| | - Alexandra A Roberts
- Australian Institute of Tropical Health and Medicine, James Cook Univiersity, Townsville, Queensland, Australia
| | - Catherine Rush
- Australian Institute of Tropical Health and Medicine, James Cook Univiersity, Townsville, Queensland, Australia
| | - Lee F Skerratt
- One Health Research Group, Melbourne Veterinary School, University of Melbourne, Werribee, Victoria, Australia
| | - Mark L Tizard
- Australian Centre for Disease Preparedness, CSIRO Health and Biosecurity, Geelong, Victoria, Australia
| | - Lee Berger
- One Health Research Group, Melbourne Veterinary School, University of Melbourne, Werribee, Victoria, Australia
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Webb RJ, Cuff C, Berger L. Glutathione-Mediated Metal Tolerance in an Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis). ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2024; 43:1583-1591. [PMID: 38726969 DOI: 10.1002/etc.5885] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Revised: 02/21/2024] [Accepted: 04/07/2024] [Indexed: 06/27/2024]
Abstract
The spread of the amphibian chytrid fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis, has resulted in amphibian declines and extinctions worldwide. Some susceptible amphibian species can persist in contaminated habitats, prompting the hypothesis that B. dendrobatidis might be sensitive to heavy metals. We tested a panel of 12 metals to rank their toxicity to B. dendrobatidis zoospores and zoosporangia during a 6-h exposure. To better understand the mechanism for metal detoxification, we also evaluated whether glutathione is required for metal tolerance by depleting cellular glutathione before metal exposure. In addition, we investigated whether prior exposure to low metal concentrations impacted tolerance of subsequent exposure, as well as identifying metal combinations that may act synergistically. Silver (Ag), cadmium (Cd), and copper (Cu) were particularly toxic to B. dendrobatidis, with zoospore minimum lethal concentration values of 0.01 mM (Ag), 0.025 mM (Cd), and 0.5 mM (Cu). These three metals along with zinc (Zn) were also inhibitory to zoosporangia, with minimum inhibitory concentration values of 0.005 mM (Ag), 0.04 mM (Cd), 0.075 mM (Cu), and 0.04 mM (Zn). The fungicidal effects of several metals was reduced when assays were conducted in nutrient medium compared with synthetic pond water, highlighting the need for careful in vitro assay design and interpretation. Glutathione depletion strongly influenced tolerance of Cd and Ag (85% and 75% less growth, respectively) and moderately influenced tolerance of Cu, Zn, and lead (37%, 18%, and 14% less growth, respectively), indicating the importance of glutathione for metal detoxification. In general, the minimum metal concentrations that inhibited growth of B. dendrobatidis far exceeded values detected in contaminated amphibian habitats in Australia, suggesting that metal contamination alone may not have a strong protective effect against chytridiomycosis. We discuss future research directions to futher understand the potential for dissolved metals to create chytrid refuges. Environ Toxicol Chem 2024;43:1583-1591. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
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Affiliation(s)
- Rebecca J Webb
- Melbourne Veterinary School, University of Melbourne, Werribee, Victoria, Australia
| | | | - Lee Berger
- Melbourne Veterinary School, University of Melbourne, Werribee, Victoria, Australia
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Mulder KP, Savage AE, Gratwicke B, Longcore JE, Bronikowski E, Evans M, Longo AV, Kurata NP, Walsh T, Pasmans F, McInerney N, Murray S, Martel A, Fleischer RC. Sequence capture identifies fastidious chytrid fungi directly from host tissue. Fungal Genet Biol 2024; 170:103858. [PMID: 38101696 DOI: 10.1016/j.fgb.2023.103858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Revised: 12/04/2023] [Accepted: 12/12/2023] [Indexed: 12/17/2023]
Abstract
The chytrid fungus Batrachochytrium dendrobatidis (Bd) was discovered in 1998 as the cause of chytridiomycosis, an emerging infectious disease causing mass declines in amphibian populations worldwide. The rapid population declines of the 1970s-1990s were likely caused by the spread of a highly virulent lineage belonging to the Bd-GPL clade that was introduced to naïve susceptible populations. Multiple genetically distinct and regional lineages of Bd have since been isolated and sequenced, greatly expanding the known biological diversity within this fungal pathogen. To date, most Bd research has been restricted to the limited number of samples that could be isolated using culturing techniques, potentially causing a selection bias for strains that can grow on media and missing other unculturable or fastidious strains that are also present on amphibians. We thus attempted to characterize potentially non-culturable genetic lineages of Bd from distinct amphibian taxa using sequence capture technology on DNA extracted from host tissue and swabs. We focused our efforts on host taxa from two different regions that likely harbored distinct Bd clades: (1) wild-caught leopard frogs (Rana) from North America, and (2) a Japanese Giant Salamander (Andrias japonicus) at the Smithsonian Institution's National Zoological Park that exhibited signs of disease and tested positive for Bd using qPCR, but multiple attempts failed to isolate and culture the strain for physiological and genetic characterization. We successfully enriched for and sequenced thousands of fungal genes from both host clades, and Bd load was positively associated with number of recovered Bd sequences. Phylogenetic reconstruction placed all the Rana-derived strains in the Bd-GPL clade. In contrast, the A. japonicus strain fell within the Bd-Asia3 clade, expanding the range of this clade and generating additional genomic data to confirm its placement. The retrieved ITS locus matched public barcoding data from wild A. japonicus and Bd infections found on other amphibians in India and China, suggesting that this uncultured clade is widespread across Asia. Our study underscores the importance of recognizing and characterizing the hidden diversity of fastidious strains in order to reconstruct the spatiotemporal and evolutionary history of Bd. The success of the sequence capture approach highlights the utility of directly sequencing pathogen DNA from host tissue to characterize cryptic diversity that is missed by culture-reliant approaches.
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Affiliation(s)
- Kevin P Mulder
- Wildlife Health Ghent, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium; Center for Conservation Genomics, Smithsonian National Zoo and Conservation Biology Institute, Washington, DC, USA.
| | - Anna E Savage
- Department of Biology, University of Central Florida, Orlando, FL, USA
| | - Brian Gratwicke
- Smithsonian's National Zoo and Conservation Biology Institute, Washington, DC, USA
| | - Joyce E Longcore
- School of Biology and Ecology, University of Maine, Orono, ME, USA
| | - Ed Bronikowski
- Smithsonian's National Zoo and Conservation Biology Institute, Washington, DC, USA
| | - Matthew Evans
- Smithsonian's National Zoo and Conservation Biology Institute, Washington, DC, USA
| | - Ana V Longo
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Naoko P Kurata
- Center for Conservation Genomics, Smithsonian National Zoo and Conservation Biology Institute, Washington, DC, USA; Department of Natural Resources and the Environment, Cornell University, Ithaca, NY, USA; Department of Ichthyology, American Museum of Natural History, New York, NY, USA
| | - Tim Walsh
- Smithsonian's National Zoo and Conservation Biology Institute, Washington, DC, USA
| | - Frank Pasmans
- Wildlife Health Ghent, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Nancy McInerney
- Center for Conservation Genomics, Smithsonian National Zoo and Conservation Biology Institute, Washington, DC, USA
| | - Suzan Murray
- Smithsonian's National Zoo and Conservation Biology Institute, Washington, DC, USA
| | - An Martel
- Wildlife Health Ghent, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Robert C Fleischer
- Center for Conservation Genomics, Smithsonian National Zoo and Conservation Biology Institute, Washington, DC, USA
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Kalinka E, Brody SM, Swafford AJM, Medina EM, Fritz-Laylin LK. Genetic transformation of the frog-killing chytrid fungus Batrachochytrium dendrobatidis. Proc Natl Acad Sci U S A 2024; 121:e2317928121. [PMID: 38236738 PMCID: PMC10823177 DOI: 10.1073/pnas.2317928121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Accepted: 12/13/2023] [Indexed: 01/23/2024] Open
Abstract
Batrachochytrium dendrobatidis (Bd), a causative agent of chytridiomycosis, is decimating amphibian populations around the world. Bd belongs to the chytrid lineage, a group of early-diverging fungi that are widely used to study fungal evolution. Like all chytrids, Bd develops from a motile form into a sessile, growth form, a transition that involves drastic changes in its cytoskeletal architecture. Efforts to study Bd cell biology, development, and pathogenicity have been limited by the lack of genetic tools with which to test hypotheses about underlying molecular mechanisms. Here, we report the development of a transient genetic transformation system for Bd. We used electroporation to deliver exogenous DNA into Bd cells and detected transgene expression for up to three generations under both heterologous and native promoters. We also adapted the transformation protocol for selection using an antibiotic resistance marker. Finally, we used this system to express fluorescent protein fusions and, as a proof of concept, expressed a genetically encoded probe for the actin cytoskeleton. Using live-cell imaging, we visualized the distribution and dynamics of polymerized actin at each stage of the Bd life cycle, as well as during key developmental transitions. This transformation system enables direct testing of key hypotheses regarding mechanisms of Bd pathogenesis. This technology also paves the way for answering fundamental questions of chytrid cell, developmental, and evolutionary biology.
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Affiliation(s)
- Erik Kalinka
- Department of Biology, University of Massachusetts, Amherst, MA01003
| | | | | | - Edgar M. Medina
- Department of Biology, University of Massachusetts, Amherst, MA01003
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De Jesús Andino F, Davydenko A, Webb RJ, Robert J. The Binding, Infection, and Promoted Growth of Batrachochytrium dendrobatidis by the Ranavirus FV3. Viruses 2024; 16:154. [PMID: 38275964 PMCID: PMC10818972 DOI: 10.3390/v16010154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/12/2024] [Accepted: 01/18/2024] [Indexed: 01/27/2024] Open
Abstract
Increasing reports suggest the occurrence of co-infection between Ranaviruses such as Frog Virus 3 (FV3) and the chytrid fungus Batrachochytrium dendrobatidis (Bd) in various amphibian species. However, the potential direct interaction of these two pathogens has not been examined to date. In this study, we investigated whether FV3 can interact with Bd in vitro using qPCR, conventional microscopy, and immunofluorescent microscopy. Our results reveal the unexpected ability of FV3 to bind, promote aggregation, productively infect, and significantly increase Bd growth in vitro. To extend these results in vivo, we assessed the impact of FV3 on Xenopus tropicalis frogs previously infected with Bd. Consistent with in vitro results, FV3 exposure to previously Bd-infected X. tropicalis significantly increased Bd loads and decreased the host's survival.
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Affiliation(s)
- Francisco De Jesús Andino
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY 14642, USA; (F.D.J.A.); (A.D.)
| | - Anton Davydenko
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY 14642, USA; (F.D.J.A.); (A.D.)
| | - Rebecca J. Webb
- Veterinary Biosciences, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia;
| | - Jacques Robert
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY 14642, USA; (F.D.J.A.); (A.D.)
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Webb RJ, Rush C, Berger L, Skerratt LF, Roberts AA. Glutathione is required for growth and cadmium tolerance in the amphibian chytrid fungus, Batrachochytrium dendrobatidis. Biochimie 2023; 220:22-30. [PMID: 38104714 DOI: 10.1016/j.biochi.2023.12.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Revised: 11/24/2023] [Accepted: 12/12/2023] [Indexed: 12/19/2023]
Abstract
Batrachochytrium dendrobatidis (Bd) is a lethal amphibian pathogen, partly due to its ability to evade the immune system of susceptible frog species. In many pathogenic fungi, the antioxidant glutathione is a virulence factor that helps neutralise oxidative stressors generated from host immune cells, as well as other environmental stressors such as heavy metals. The role of glutathione in stress tolerance in Bd has not been investigated. Here, we examine the changes in the glutathione pool after stress exposure and quantify the effect of glutathione depletion on cell growth and stress tolerance. Depletion of glutathione repressed growth and release of zoospores, suggesting that glutathione is essential for life cycle completion in Bd. Supplementation with <2 mM exogenous glutathione accelerated zoospore development, but concentrations >2 mM were strongly inhibitory to Bd cells. While hydrogen peroxide exposure lowered the total cellular glutathione levels by 42 %, glutathione depletion did not increase the sensitivity to hydrogen peroxide. Exposure to cadmium increased total cellular glutathione levels by 93 %. Glutathione-depleted cells were more sensitive to cadmium, and this effect was attenuated by glutathione supplementation, suggesting that glutathione plays an important role in cadmium tolerance. The effects of heat and salt were exacerbated by the addition of exogenous glutathione. The impact of glutathione levels on Bd stress sensitivity may help explain differences in host susceptibility to chytridiomycosis and may provide opportunities for synergistic therapeutics.
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Affiliation(s)
- Rebecca J Webb
- James Cook University, Townsville, QLD, 4811, Australia; Melbourne Veterinary School, University of Melbourne, Werribee, VIC, 3030, Australia.
| | | | - Lee Berger
- Melbourne Veterinary School, University of Melbourne, Werribee, VIC, 3030, Australia
| | - Lee F Skerratt
- Melbourne Veterinary School, University of Melbourne, Werribee, VIC, 3030, Australia
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Robinson KA, Prostak SM, Campbell Grant EH, Fritz-Laylin LK. Amphibian mucus triggers a developmental transition in the frog-killing chytrid fungus. Curr Biol 2022; 32:2765-2771.e4. [DOI: 10.1016/j.cub.2022.04.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 03/25/2022] [Accepted: 04/04/2022] [Indexed: 12/20/2022]
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