E is for Epibiotic/Epibiont

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As a part of the A-Z Photographic Glossary of Biological Terms challenge, today it is E for Epibiotic/Epibiont, as illustrated by the Eastern Red-backed Salamander (Plethodon cinereus), native to the mid-Atlantic region of the United States.

Red-backed salamanders come in two primary colour forms- lead-backed and red-backed and are very important indicator species for the health of the moist woodlands they inhabit- if the deciduous woodland habitats in which they are found are degraded or severely modified, these salamanders soon disappear.

However, what is unique with this species is that the skin of Red-backed salamanders has been found to contain Lysobacter gummosus, an epibiotic bacterium which produces a chemical that inhibits the growth of certain pathogenic fungi. An epibiotic organism (an epibiont) is one that lives on the surface of another organism and in this case, the bacterium that lives on the surface of this salamander produces the chemical 2,4-diacetylphloroglucinol.

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Importantly, the ability of this salamander to host Lysobacter gummosus and the chemical this epibiont produces, has started to show positive results in combatting the fungal pathogen Batrachochytrium dendrobatidis which causes amphibian mortality and is associated with population declines and extinctions throughout Central America and the rest of the world! It is now also being investigated as a possible biological control application for horticultural and agricultural use in controlling certain disease issues in plants including the dreaded Fusarium, as well as a strain of ‘leaf spot’ (Bipolaris sorokiniana), a ‘rust’ (Uromyces appendiculatus), as well as the soilborne disease known as ‘brown patch’ in grasses (Rhizoctonia solani) which is also responsible for ‘black scurf’ of potatoes, ‘bare patch’ of cereals, and ‘root rot’ of sugar beet.

An important study looking at how Lysobacter gummosus can help prevent amphibian population declines is Harris, Reid N; James, Timothy Y; Lauer, Antje; Simon, Mary Alice; and Patel, Amit (2006). “Amphibian Pathogen Batrachochytrium dendrobatidis Is Inhibited by the Cutaneous Bacteria of Amphibian Species”. EcoHealth 3, 53–56.

One study documenting the symbiosis between Lysobacter gummosus and the Red-backed salamander is Brucker, Robert M.; Baylor, Cambria M.; Walters, Robert L.; Lauer, Antje; Harris, Reid N.; Minbiole, Kevin P. C. (2008). “The Identification of 2,4-diacetylphloroglucinol as an Antifungal Metabolite Produced by Cutaneous Bacteria of the Salamander Plethodon cinereus”. Journal of Chemical Ecology 34 (1): 39–43.

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