Batrachochytrium dendrobatidis

Introduction

Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.

Fungal disease has emerged as an increasing threat to a number of different organisms, especially amphibian species. Batrachochytrium dendrobatidis, a chytrid fungus that causes the infectious disease chytridiomycosis has been found to be the major cause of amphibian death caused by fungal infection. B. dendrobatidis infects the superficial, keratin-containing layers of amphibian skin. The infection then spreads across the skin, causing it to thicken and slough off. This thickening interferes with osmoregulation and eventually leads to death¹.It has been found to affect at least 93 amphibian species in frogs, toads (Anura) and salamanders (Caudata)². Evidence of B. dendrobatidis has been found worldwide and is believed to have originated in Africa and spread through the trade of Xenopus laevis³. B. dendrobatidis has been responsible for the epidemic illness and death of amphibian populations in Australia, New Zealand, Europe, Central America, and the United States⁴.

Batrachochytrium dendrobatidis

Physiology
Temperature has an effect on mortality rates associated with B. dendrobatidis. B. dendrobatidis can grows in 4-25 oC, but grows optimally in 17-25 ^oC. Nitrogen has a strong effect on the growth of B. dendrobatidis. It is possible that B. dendrobatidis grow in keratinized epidermal cells because they are dead and easier to invade ⁵.

Morphology
B. dendrobatidis is identified by its intracellular flask-shaped sporangia (spore containing bodies) and septate thalli. The fungus produces smooth-walled zoosporangia (zoospore containing bodies), which are generally spherical in shape. Each zoosporangium (5.2 ± 0.72 μm⁶) produces a single discharge tube, which penetrates the skin and releases mature zoospores. The zoospores (3-5 μm in diameter) are oval shaped and have a single posterior flagellum (19–20 μm in length), which allows it to move in water. There is little morphological difference in B. dendrobatidis strains^4,7

Life Cycle
B. dendrobatidis progresses from a zoospore to a thallus (growing organism), which then produces a single zoosporangium (container for zoospores). The sporangium (contents of the zoosporangium) divides into new zoospores that exit the sporangium through one or more papillae. B. dendrobatidis has not been shown to reproduce sexually. The duration of the life cycle in vitro is 4 to 5 d at 22°C and due to the similarity in life cycles in vivo and in vitro, duration is assumed to be the same in both. B. dendrobatidis infects the superficial epidermis (stratum granulosum and stratum corneum) in amphibians. Immature sporangia are found in deeper cells, while mature zoosporangia and empty sporangia are found in the outer keratinized layers of the skin. Zoospores are released into the environment by discharge tubes that project out of the skin surface⁸.

Section 2

Include some current research in each topic, with at least one figure showing data.

Section 3

Include some current research in each topic, with at least one figure showing data.

Conclusion

Overall paper length should be 3,000 words, with at least 3 figures.

References

1. Berger, Lee, et al. "Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America." Proceedings of the National Academy of Sciences 95.15 (1998): 9031-9036

2. Parris, Matthew J., and Joseph G. Beaudoin. "Chytridiomycosis impacts predator-prey interactions in larval amphibian communities." Oecologia 140.4 (2004): 626-632.

3. Berger, Lee, et al. "Virulence of the amphibian chytrid fungus Batrachochytrium dendrobatidis varies with the strain." Diseases of Aquatic Organisms 68.1 (2005): 47.

4. Johnson, Megan L., and Richard Speare. "Survival of Batrachochytrium dendrobatidis in water: quarantine and disease control implications." Emerging Infectious Diseases 9.8 (2003): 922.

5. Piotrowski, Jeffrey S., Seanna L. Annis, and Joyce E. Longcore. "Physiology of Batrachochytrium dendrobatidis, a chytrid pathogen of amphibians." Mycologia 96.1 (2004): 9-15.

6. Weldon, Ché, et al. "Origin of the amphibian chytrid fungus." Emerging infectious diseases 10.12 (2004): 2100.

7. Longcore, Joyce E., Allan P. Pessier, and Donald K. Nichols. "Batrachochytrium dendrobatidis gen. et sp. nov., a chytrid pathogenic to amphibians." Mycologia (1999): 219-227.

8. Berger, Lee, et al. "Life cycle stages of the amphibian chytrid Batrachochytrium dendrobatidis." Diseases of aquatic organisms 68 (2005): 51-63

9. Johnson, Megan L., and Richard Speare. "Survival of Batrachochytrium dendrobatidis in water: quarantine and disease control implications." Emerging Infectious Diseases 9.8 (2003): 922.

10. Piotrowski, Jeffrey S., Seanna L. Annis, and Joyce E. Longcore. "Physiology of Batrachochytrium dendrobatidis, a chytrid pathogen of amphibians." Mycologia 96.1 (2004): 9-15.

Edited by student of Joan Slonczewski for BIOL 238 Microbiology, 2009, Kenyon College.