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| The next great discovery in predacious fungi did not occur until 1933, when Drechsler, over the course of several publications, described the discovery of never before seen predatory activity associated with nematode and amoeboid digestion. Further publications describe Zoopagaceae, a family of predatory fungi, feeding mainly on amoebae and decaying organic matter. In 1937, Drechsler's research resulted in the detailed activity of ''A. oligospora'', ''A. superba'', ''D. candida'' and ''D. ellipsospora''. | The next great discovery in predacious fungi did not occur until 1933, when Drechsler, over the course of several publications, described the discovery of never before seen predatory activity associated with nematode and amoeboid digestion. Further publications describe Zoopagaceae, a family of predatory fungi, feeding mainly on amoebae and decaying organic matter. In 1937, Drechsler's research resulted in the detailed activity of ''A. oligospora'', ''A. superba'', ''D. candida'' and ''D. ellipsospora''. | ||
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| ==Common Environments== | ==Common Environments== | ||
Revision as of 10:05, 20 March 2013
Contents |
'Predatory' fungi
Fungi can act as parasites and pathogens in a host of species from plants to animals however their relationship with soil nematodes is unique. Over 200 species have been identified that have mechanisms facilitating identification, luring and ambush of prey (yang et al).
Definitions
- Predatory fungi
- Definition
- Endoparasitic fungi
- Definition
History
The earliest known record of predatory fungi occurs in classical reports describing the observation of the capture and digestion of nematodes by the fungi Arthrobotrys oligospora, one of the most common predacious fungi. The A. oligospora was originally classified as a saprophyte in 1852, however, 20 years after its discovery, germinating spores were observed producing mycelium with curving hyphae forming a system of loops, the significance of which remained unknown at the time. It was not until research preformed in 1888 by Dr. Wilhelm Zopf was the purpose of these loops discovered. Zopf grew cultures of A. oligospora, in the presence of nematodes and demonstrated that the nematode eelworms were caught by the loops, where the nematode remained until its death. He then observed how the fungi introduced absorptive hyphae into the body of the nematode and consume its carcass.
The discovery of predatory A. oligospora occurred at a time similar to that of another fungi of intrest, Dactylella ellipsospora. This fungi was first described in 1851 under the genus Menispora; it was later given the title Dactylella upon being discovered on decaying wood. The predatory effect of D. ellipsospora wasn't discovered until 1937 by Dr. Charles Drechsler. Publications by Drechsler describe D. ellipsospora and the formation of adhesive knobs along its hyphae used in the capture and digestion of nematodes.
The next great discovery in predacious fungi did not occur until 1933, when Drechsler, over the course of several publications, described the discovery of never before seen predatory activity associated with nematode and amoeboid digestion. Further publications describe Zoopagaceae, a family of predatory fungi, feeding mainly on amoebae and decaying organic matter. In 1937, Drechsler's research resulted in the detailed activity of A. oligospora, A. superba, D. candida and D. ellipsospora.
Common Environments
Environmental niches which favour successful growth of amoebae and nematode worms are typically areas where predatory fungi are most abundant. However, high host count in an area does not necessarily guarantee the presence of predatory fungi.
A few principal terrestrial habitats have been identified through various literature. These environments include leaf mould, decaying wood, partly decayed plant remains, dung, and living bryophytes- all of which are found in soil.
- Leaf mould
Many fungi thrive in this environment, however it not the most prevalent condition for predatory fungi specifically, though some may still be found in such areas.
- Decaying wood
Decaying wood is one of the most dominant habitats for predatory fungi. Wood in advanced stages of the decaying process, is often rich in nematode species, thus substantially resonating with the life of predatory fungi and providing ideal host trapping conditions.
- Plant remains
Decaying plant remains, especially those leaves and stems significantly softened by the early stages of decay, are also often rich in predatory fungi
- Dung
Dung is also a typical environment in which predatory fungi thrive. It is important to note that as the dung ages, the organisms colonized within it change, and the oldest material usually contains the most variance in predatory fungi species.
- Living Bryophytes
Bryophytes appear to be the most prevalent and successful predatory fungi habitat. Mosses, especially when moist, are an optimal environment for large nematode worms and thus provide extremely favourable host trapping environments.
Interestingly, some predatory fungi species can be obtained from aquatic habitats, though they are regarded as terrestrial. True aquatic forms such as Zoophagus insidians do exist however.
Mechanisms of Predation
With the definition of predacious fungi a few food sources are available to this classification of fungi. Predacious fungi have been observed feeding on nematodes amoebae, and collembola.
Nematode Trapping
Nematophagous or nematode-killing fungi have evolved traps along their hyphae which can secrete nematode-attracting chemicals and are activated when prey is detected. Specific species like Arthrobotrys oligospora can even increase or decrease the number of traps expressed on their hyphae when nematodes or chemicals secreted by them are detected. (textbook)
Types of traps:
Adhesive Traps
These multicellular traps contain electron dense bodies and adhesive surface polymers. This means the tight binding of fungus and nematode is caused by interaction between sugars and other charged molecules on the cell surfaces. Trapping occurs when the nematode makes contact with the trap’s surface. (Yang et al)
Subtypes:
- Adhesive network- Amongst the most common fungal traps. Hypha branches form loops and these loops form a three-dimensional network for which attract and entangle approaching nematodes. These loops typically have a diameter of 20um.
- Adhesive knob- It is hypothesized that ring and network traps evolved from adhesive knobs in orbiliaceous fungi (those belonging to the order Orbiliales). These traps are composed of a bulbous cell attached at the terminal end of a hyphal stalk. They are usually closely spaced along the hypha to maximize the chances of successfully trapping the nematode.
- Non-constricting ring- Always accompany adhesive knobs. These form from lateral branches which loop around forming three-celled rings that attach to a stalk.
- Adhesive column- A hyphal branch composed of a few inflated cells.
Constricting Rings
Similar to the non-constricting ring, this is a three-celled trap attracts nematodes searching for food through the ring. The unique feature of the constricting ring is that it actively captures the prey. When the nematode is sensed chemically or physically, the ring cells will inflate within seconds thus trapping the nematode along its length. This is the most sophisticated trapping mechanism. (Yang et al)
Post-trapping Digestion
When the nematode has become sufficiently bound to the adhesive layer or crushed by the constrictive ring, hypha produce a penetration peg which punctures the outer layer of the nematode. Infection bulbs full of digestive enzymes inflate within the nematode and erupt initiating absorptive nutrition. Absorptive nutrition involves the digestion of nutrients outside of the fungal cell followed by absorption of the products. These products fuel further hyphal growth and hypha can even begin to grow out of the dead nematode.(txt)
Some Species of Fungi and Their Use of Various Entrapments
Listed below are some Nematophagus fungi and their methods of entrapment. Some fungi are capable of using multiple methods in order to ensnare their prey, while others are fairly specific in their approach. In almost all instances, the fungi will utilize an attraction mechanism in order to lure in their prey.
Three Dimensional Web (Arthrobotrys oligospora)
One of the most common Predatory fungi, Arthrobotrys utilizies a three dimensional web in order to capture its prey(4) see figure 1.
Adhesive Knobs and Non Constricting Rings (Dactylaria candida)
This species of fungi utilizes adhesive knobs paired with non constricting rings. The formation of this dual structure for entrapment involves the formation of an inflated cell along the route of the hyphae (Knob)(6) and the production of a three membered ring which has no inflation upon nematode presence. This type of trapping device is paired with an attraction molecule for the fungi along with lectins on the adhesive cell surface.
Contractile Rings (Arthrobotyrys dactyloides)
The contractile ring is formed via a three cell protrusion from the mycelium which loops around in order to form the termed ring. Arthroboytrys dactyloides will produce nematode attraction compounds, one of which have been identified as carbon dioxide (3). Once the nematode has been lured to the constricting ring, A. dactyloides mechanically traps the Nematode by expansion of the cells in the ring, and is digested by release of ammonia (3). Notes on Predacity
It has been shown that the most effective fungi are the ones with the most motility in their environment, as predator prey interaction depends on frequency of interaction (2). With that being said, density of the fungi and density of the prey are very important factors in affecting the effectiveness as highly dense redatores can limit the population in an area of the prey, and large populations of prey, limit substrate for fungi to grow (1).
Food Sources and Methods of Entrapment
Zoophagus produces in what was described by Howard Whistler from the University of Washington as “lethal lollipops.” The swollen ends of the fungi have a ball at the end (lollipop) in which attracts rotifers. These microscopic animals attach to the ends by their mouths and try to swallow the “lollipop” but, end up getting stuck. Once they become attached, the tip of the hyphae sprouts and colonizes the organism [2].
Like many organisms, fungi also must obtain their source of protein. Fungi and plants obtain their share of proteins through nitrogen. Wood-decaying fungi have the challenge of obtaining their source of fungi by living in nitrogen poor environments. They face the carbon/nitrogen ration of 500:1. There are known to be a substantial amount of fungi in which exhibit a Jekyll-Hyde type characteristic in which they can switch between being herbivorous and carnivorous as it pertains to their needs.
The oyster mushroom (Pleurotus ostreatus) and the wood blewit (Lepista nuda) have been found to exhibit this sort of behavior (ref). The oyster mushroom produces secretory cells that in which contain a droplet of fluid. Once the nematode comes in contact with the fluid, the toxins within the fluid cause structural damage and immobilizes is it. Once the nematode has become completely paralyzed, the hypha of the fungus will grow into the nematode’s mouth and begin to digest the remaining living tissue[3].
Benefits and Practical Applications
Ecological
Notes and References
Barron, George (1992). Jekyll-Hyde mushrooms. Natural History. Vol. 101, Issue 3
Duddington, C. L. (1951). The ecology of predacious fungi: I. Preliminary survey. Transactions of the British Mycological Society, 34(3), 322-331.
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