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Endophytes – the chemical synthesizers inside plants - A Free Review

Posted on 24. February, 2015.

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Endophytes are microbial entities that live within living tissues of plants.
In most cases their relationship with the host plant is symbiotic and probably mutualistic. Many are capable of synthesizing bio-active compounds that can be used by the plant for defense against pathogenic fungi and bacteria. Some of these compounds have proven useful for novel drug discovery.

Virtually all plants are hosts to endophytic microbes (usually bacteria and fungi). Most people are probably aware that bacteria are ubiquitous; the human mouth, for example, is home to a huge number of different strains. However, fewer may be aware that bacteria and fungi can be found not only on the surface of plants (as epiphytes), but also as endophytes, colonizing the tissues between plant cells and possibly within plant cells. Endophytes may be defined as microbes that colonize living internal tissues of plants without causing any immediate, overt negative effects. This particular definition implies a symbiotic or mutualistic relationship between the host plant and the endophytic microbe. On the other hand, Stone et. al in their review, suggest that relationships other than mutualistic interactions in endophytes are recognized and should be anticipated. Similarly, Strobel and others suggest that the relationship can range from mutualistic to bordering on pathogenic. The most frequently encountered endophytes are fungi, and it has been estimated that there may be over a million different fungal species on this Earth, of which only a small fraction (ca 5%) has been identified. There are also many bacteria that exist as plant endophytes, and indeed in many instances they coexist with the endophytic fungi. 
By encouraging the endophytes to grow outside the plant in nutrient rich media, it is possible to harvest the bio-active compounds that they produce. However, much needs to be discovered and understood about the host/endophyte relationship before we can fully utilize endophytes in the discovery of medicinally important compounds.

Read the full article, for free, in Science Progress, Volume 87, Number 2, May 2004, pp. 79-99.

Authors: Noel L Owen and Nicholas Hundley

Keywords: endophytes, fungi, bacteria, bio-active compounds

Image: Taxol - an anti-cancer compound synthesized by the Pacific Yew tree and by a fungus associated with the tree.