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Germ tube mediated invasion of Batrachochytrium dendrobatidis in amphibian skin is host dependent.

Van Rooij P, Martel A, D'Herde K, Brutyn M, Croubels S, Ducatelle R, Haesebrouck F, Pasmans F - PLoS ONE (2012)

Bottom Line: Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm.Only the superficial epidermis was affected.These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium. pascale.vanrooij@ugent.be

ABSTRACT
Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis, a fungal skin disease in amphibians and driver of worldwide amphibian declines.We focussed on the early stages of infection by Bd in 3 amphibian species with a differential susceptibility to chytridiomycosis. Skin explants of Alytes muletensis, Litoria caerulea and Xenopus leavis were exposed to Bd in an Ussing chamber for 3 to 5 days. Early interactions of Bd with amphibian skin were observed using light microscopy and transmission electron microscopy. To validate the observations in vitro, comparison was made with skin from experimentally infected frogs. Additional in vitro experiments were performed to elucidate the process of intracellular colonization in L. caerulea. Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm. Inoculation of A. muletensis and L. caerulea skin was followed within 24 h by endobiotic development, with sporangia located intracellularly in the skin. Evidence is provided of how intracellular colonization is established and how colonization by Bd proceeds to deeper skin layers. Older thalli develop rhizoid-like structures that spread to deeper skin layers, form a swelling inside the host cell to finally give rise to a new thallus. In X. laevis, interaction of Bd with skin was limited to an epibiotic state, with sporangia developing upon the skin. Only the superficial epidermis was affected. Epidermal cells seemed to be used as a nutrient source without development of intracellular thalli. The in vitro data agreed with the results obtained after experimental infection of the studied frog species. These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.

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Intracellular colonization of Litoria caerulea skin by Bd.(A–E): in vitro, (F): in vivo. (A) invasion of the stratum corneum by a germ tube (white arrow) at 2 hour post infection (hpi); (B) strong elongation of the germ tube (white arrow) into the stratum spinosum at 8 hpi; (C) development of intracellular chytrid thalli (white arrow) at the end of a germ tube at 24 hpi; rhizoid-like structures (black arrow) arise from newly developed chytrid thalli; (D) development of a new chytrid thallus at 24 hpi; a swelling is formed at the end of a rhizoid-like structure, a thin cell wall is formed and the cell content of the mother thallus (white arrow) is transferred into the new daughter thallus (white circle); a new thallus in a later developmental stage (black circle); (E) thalli connected by a rhizoid-like structure (white arrow); remnants of a germling, after having injected its cell content into a new intracellular thallus (black arrow); (F) mother thallus connected to a newly formed daughter thallus by a rhizoid-like structure (white arrow) at 14 days post infection. Gomori methenamine silver stain, scale bar = 10 µm.
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pone-0041481-g006: Intracellular colonization of Litoria caerulea skin by Bd.(A–E): in vitro, (F): in vivo. (A) invasion of the stratum corneum by a germ tube (white arrow) at 2 hour post infection (hpi); (B) strong elongation of the germ tube (white arrow) into the stratum spinosum at 8 hpi; (C) development of intracellular chytrid thalli (white arrow) at the end of a germ tube at 24 hpi; rhizoid-like structures (black arrow) arise from newly developed chytrid thalli; (D) development of a new chytrid thallus at 24 hpi; a swelling is formed at the end of a rhizoid-like structure, a thin cell wall is formed and the cell content of the mother thallus (white arrow) is transferred into the new daughter thallus (white circle); a new thallus in a later developmental stage (black circle); (E) thalli connected by a rhizoid-like structure (white arrow); remnants of a germling, after having injected its cell content into a new intracellular thallus (black arrow); (F) mother thallus connected to a newly formed daughter thallus by a rhizoid-like structure (white arrow) at 14 days post infection. Gomori methenamine silver stain, scale bar = 10 µm.

Mentions: A more detailed study of the invasion process in L. caerulea showed that at earliest, frog skin was invaded by germ tubes 2 hours after exposure to Bd (Fig. 6A,B). Eight, 16 and 24 hours of exposure to Bd were defined as most critical time-points to study intracellular colonization and were repeated in triplicate during additional in vitro assays. Chytrid thalli developing intracellularly were observed at 16 to 24 hours after exposure. In one out of the 3 repeats, intracellular colonization occurred 8 hours after exposure. In this experiment the stratum corneum had already detached from the stratum spinosum, probably rendering the epidermis more accessible.


Germ tube mediated invasion of Batrachochytrium dendrobatidis in amphibian skin is host dependent.

Van Rooij P, Martel A, D'Herde K, Brutyn M, Croubels S, Ducatelle R, Haesebrouck F, Pasmans F - PLoS ONE (2012)

Intracellular colonization of Litoria caerulea skin by Bd.(A–E): in vitro, (F): in vivo. (A) invasion of the stratum corneum by a germ tube (white arrow) at 2 hour post infection (hpi); (B) strong elongation of the germ tube (white arrow) into the stratum spinosum at 8 hpi; (C) development of intracellular chytrid thalli (white arrow) at the end of a germ tube at 24 hpi; rhizoid-like structures (black arrow) arise from newly developed chytrid thalli; (D) development of a new chytrid thallus at 24 hpi; a swelling is formed at the end of a rhizoid-like structure, a thin cell wall is formed and the cell content of the mother thallus (white arrow) is transferred into the new daughter thallus (white circle); a new thallus in a later developmental stage (black circle); (E) thalli connected by a rhizoid-like structure (white arrow); remnants of a germling, after having injected its cell content into a new intracellular thallus (black arrow); (F) mother thallus connected to a newly formed daughter thallus by a rhizoid-like structure (white arrow) at 14 days post infection. Gomori methenamine silver stain, scale bar = 10 µm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3401113&req=5

pone-0041481-g006: Intracellular colonization of Litoria caerulea skin by Bd.(A–E): in vitro, (F): in vivo. (A) invasion of the stratum corneum by a germ tube (white arrow) at 2 hour post infection (hpi); (B) strong elongation of the germ tube (white arrow) into the stratum spinosum at 8 hpi; (C) development of intracellular chytrid thalli (white arrow) at the end of a germ tube at 24 hpi; rhizoid-like structures (black arrow) arise from newly developed chytrid thalli; (D) development of a new chytrid thallus at 24 hpi; a swelling is formed at the end of a rhizoid-like structure, a thin cell wall is formed and the cell content of the mother thallus (white arrow) is transferred into the new daughter thallus (white circle); a new thallus in a later developmental stage (black circle); (E) thalli connected by a rhizoid-like structure (white arrow); remnants of a germling, after having injected its cell content into a new intracellular thallus (black arrow); (F) mother thallus connected to a newly formed daughter thallus by a rhizoid-like structure (white arrow) at 14 days post infection. Gomori methenamine silver stain, scale bar = 10 µm.
Mentions: A more detailed study of the invasion process in L. caerulea showed that at earliest, frog skin was invaded by germ tubes 2 hours after exposure to Bd (Fig. 6A,B). Eight, 16 and 24 hours of exposure to Bd were defined as most critical time-points to study intracellular colonization and were repeated in triplicate during additional in vitro assays. Chytrid thalli developing intracellularly were observed at 16 to 24 hours after exposure. In one out of the 3 repeats, intracellular colonization occurred 8 hours after exposure. In this experiment the stratum corneum had already detached from the stratum spinosum, probably rendering the epidermis more accessible.

Bottom Line: Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm.Only the superficial epidermis was affected.These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium. pascale.vanrooij@ugent.be

ABSTRACT
Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis, a fungal skin disease in amphibians and driver of worldwide amphibian declines.We focussed on the early stages of infection by Bd in 3 amphibian species with a differential susceptibility to chytridiomycosis. Skin explants of Alytes muletensis, Litoria caerulea and Xenopus leavis were exposed to Bd in an Ussing chamber for 3 to 5 days. Early interactions of Bd with amphibian skin were observed using light microscopy and transmission electron microscopy. To validate the observations in vitro, comparison was made with skin from experimentally infected frogs. Additional in vitro experiments were performed to elucidate the process of intracellular colonization in L. caerulea. Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm. Inoculation of A. muletensis and L. caerulea skin was followed within 24 h by endobiotic development, with sporangia located intracellularly in the skin. Evidence is provided of how intracellular colonization is established and how colonization by Bd proceeds to deeper skin layers. Older thalli develop rhizoid-like structures that spread to deeper skin layers, form a swelling inside the host cell to finally give rise to a new thallus. In X. laevis, interaction of Bd with skin was limited to an epibiotic state, with sporangia developing upon the skin. Only the superficial epidermis was affected. Epidermal cells seemed to be used as a nutrient source without development of intracellular thalli. The in vitro data agreed with the results obtained after experimental infection of the studied frog species. These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.

Show MeSH
Related in: MedlinePlus