| Arthrobotrys oligospora | |
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| Species: | A. oligospora
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| Arthrobotrys oligospora Georg Fresenius (1850)
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Arthrobotrys oligospora was discovered in Europe in 1850 by Georg Fresenius.[1][2] 'A. oligospora' is the model organism for interactions between fungi and nematodes.[2] It is the most common nematode capturing fungus,[3][4][5] and most widespread nematode capturing fungus.[2][6] It was the first species of fungi that was identified as a nematode trapping fungus.[6][2] The species name, oligospora, derives from the greek words ολιγο 'oligo' meaning few and σπορά 'spora' meaning spore.
Growth and morphology
editThis fungus undergoes reproduction using 2 cell pear-shaped conidia, of unequal size, [7][4] on conidiophores.[7] The germ tube erupts from the smaller cell.[7] In environments rich with nematodes, the spores range from 22-32 by 12-20 micrometers,[7][4] though the spores are smaller in environments devoid of nematodes.[7][4] Conidium germination has a success rate of 100% but the formation of trapping organs are not always observed.[6] Conidia have been found to disintegrate both in the air and on impact with an agar plate.[8] Condiophores and conidia grow from hyphae sprouted outside of a trapped dead nematode,[2] and condiophores have been found to change and grow into art of the adhesive net.[2] A fungal colony can grow as large as 3.8-6.5cm in diameter,[6] and appear to be transparent, pale pink or yellow in color.[6] The optimal growth temperature for the fungus in a nematode free environment and a nematode infested environment is 20 °C (68 °F) and 25 °C (77 °F), respectively.[6] Growth was found to be less continuous in darkness than in light.[6]
Physiology
editA. oligospora is considered a saprobe and is more saprotrophic than other nematode capturing fungi.[6][2] At first the fungus was considered largely saprophytic in nature but this was later determined to be untrue.[4] Saprophytic growth uses D-xylose, D-mannose, and cellobiose.[6] The fungus uses nitrite, nitrate, and ammonium for its nitrogen sources and uses pectin, cellulose, and chitin for its carbon sources.[6] When predating on nematodes, the fungus uses cellobiose, L-asparagine, L-arginine, DL glutamic acid for its carbon and nitrogen sources.[6]
Nematode capturing
editPredation of nematodes occurs in low nitrogen environments,[9] as the nematode becomes the main nitrogen source for the fungi.[2] It has been found that the presence of ammonium causes a higher decrease of predation when compared to presence of nitrate or nitrite.[3] Adding green manure or carbohydrates has been found to increase nematode trapping behaviors.[6] A complex 3 dimensional net of hyphae is formed to trap the nematodes in a pH 4.9-8.1 and temperature less than 37 °C (99 °F).[6][9][8][5] Nematodes and nemin (nematode extract) were found to stimulate net formation.[6][2] Nematodes are not as attracted to A. oligospora without traps as A. Oligospora with traps indicating nematode attracting pheromones were likely used.[9][10]
A full net is not needed to catch nematodes as smaller nematodes can be caught with a single loop.[2] Lectins are used in attaching nematode to fungi[9] The entire surface of net is covered in adhesive material.[8][2] Strong adhesion keeps the nematode trapped and when the nematode struggles, it often results in multiple points of adhesion of the nematode to the net.[10][8] It was even found that the adhesion of the nematode to the fungus remained under washing of agar plate with water.[8] The net is flexible which results in 'hyphal drag' tiring the nematode.[8] Multiple points of adhesion and 'hyphal drag' allow the net to be capable of catching both large and small nematodes easily.[8] In vitro, bait nematodes are consumed often leaving Bunonema nematodes.[8]
A substance found in paralyzed nematodes was found to be capable of paralyzing healthy nematodes,[6][8] and it was later determined that a paralyzing substance, Subtilisin (A serine protease),[11] is excreted into nematode.[8][2] An unstable toxin was thought to be made by the fungus,[6][8] and it was later found that toxic levels of linoleic acid for nematodes (lethal dose of linoleic acid for C. elegans is 5–10 μg/ml)[12] were found in the fungus.[12][5] Enzymatic hyphal invasion, likely using collagenases which are found in 'Arthrobotrys',[2] of a trapped nematode is followed by the digestion of contents of the nematode.[9][8] Shortly after hyphal invasion, a hyphal bulb appears where hyphae grow outwards from the bulb along the entire body of the nematode.[8]
Not all nematodes are caught by the net as the nematode needs to be in contact with the net for a short period of time in order for adhesion to occur.[8] Nematodes were found to quickly move away from any net followed by curling if instantaneous contact occurs.[8] [13] The nematode then proceeds to move forward until out of the area of the net and unless prolonged contact is made the nematode is safe.[8] This means one or several instantaneous contacts are not enough for adhesion between the nematode and net to occur.[8]
No competing fungi or bacteria are found in nematodes which are being consumed by the fungus which means it is possible an antibiotic is released inside the nematode.[8] In 1993, secondary metabolites (oligosporon, oligosporol A, and oligosporal B) which can act as antibiotics were found in the fungus.[2][12] Oligosporon, oligosporol A, oligosporal B have hemolytic effects and are cytotoxic to nematodes, however they are not toxic to the C. elegans.[12] Other oligosporon-type secondary metabolites also found in A. oligospora include (4S,5R,6R)-4′,5′- dihydrooligosporon, (4S,5R,6R)-hydroxyoligosporon, and (4S,5R,6R)-10′11 ′-epoxyoligosporon.[12]
Net formation
editA branch of hyphae grows out of a vegetative hyphae eventually arching back to the parent hyphae and fuses with it to make a loop.[8][7][3] This process repeats from any hyphae along any existing branches or a new parent hyphae.[8][3] The nets are immediately adhesive[8], and hyphae in the loop have different organelles to trap nematodes which are not found in vegetative cells.[2]
Habitat and ecology
editA. oligospora has been found in many different geographical regions which include Asia, Africa, North America & South America and Australasia.[2] Some countries it has been found in include Turkmenistan, Azerbaijan, Poland, Canada, New Zealand, and India.[6] The presence of insects infected by nematodes increased presence of A. oligospora but not other nematode capturing fungi.[2]
The fungus can be found in soil in grassland, shrubland, plantations, sheep and cattle yards,[6] and domesticated and non-domesticated animal feces[2]. It colonizes forest steppe soil, mixed forest soil, and Mediterranean brown soil (pH 6.9-8.0) where the pH can be as low as 4.5, but is typically above 5.5.[6] The fungus has also been found in aquatic environments,[2] and heavily polluted areas, specifically heavy metal poisoned mines, fungicide, or nematicide infested soil,[2][5] decayed plant material, leaves, roots, moss,[6] and in the rhizosphere of various bean plants, barley,[6][2] and the tomato plant.[2] Larger populations of the fungus can be found in late spring and summer.[5]
Industrial uses
editThe fungus is a biological indicator of nematodes.[2] The annual global cost of plant-parasitic nematodes is approximately 100 billion USD.[12] Nematode capturing fungi such as the A. oligospora can be used to control growth of nematodes.[6][5] This means that they can be potentially used as a bio-control agent to protect crops against nematode infestations.[2] This may not be feasible since the nematodes occasionally eat the fungi.[6]
References
edit- ^ Fresenius, Georg (1850). Beiträge zur mykologie.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x Niu, Xue-Mei; Zhang, Ke-Qin (2011). "Arthrobotrys oligospora a model organism for understanding the interaction between fungi and nematodes". Mycology. 2 (2): 59–78.
- ^ a b c d Duddington, C; Wyborn, C (1972). "Recent Research on the Nematophagous Hyphomycetes". Botanical Review. 38: 545–562.
- ^ a b c d e Dreschler, Charles (1937). "Some Hyphomycetes That Prey on Free-Living Terricolous Nematodes". Mycologia. 29 (4): 447–552.
- ^ a b c d e f Zhang, Ke-Qin; Hyde, Kevin; Zhang, Ying; Yang, Jinkui; Li, Guo-Hang (2014). Nematode-trapping Fungi. New York: Dordrecht: Springer. pp. 213, 215, 222, 316, .
{{cite book}}: CS1 maint: extra punctuation (link) - ^ a b c d e f g h i j k l m n o p q r s t u v w Dosch, Klaus; Gams, Walter; Traute-Heidi, Anderson (1980). Compednium of soil fungi. New York: Academic Press (London) LTD. pp. 60–63.
- ^ a b c d e f Duddington, C (1955). "Fungi That Attack Microscopic Animals". Botanical Review. 21 (7): 377–439.
- ^ a b c d e f g h i j k l m n o p q r s t u Barron, George (1977). The Nematode-Destroying Fungi. Guelph: Canadian Biological Publications Ltd. pp. 27–37, 93–95, 106, 111.
- ^ a b c d e Alexopoulos, Constantine; Mims, Charles; Blackwell, Meredith (1996). Introductory Mycology (4th edition ed.). Toronto: John Wiley & Sons, Inc. p. 235.
{{cite book}}:|edition=has extra text (help) - ^ a b Nordbring-Hertz, Birgit; Jansson, Hans‐Börje; Stålhammar-Carlemalm, Margaretha (1977). "Interactions Between Nematophagous Fungi and Nematodes". Ecological Bulletins. 25: 483–484.
- ^ Nordbring-Hertz, Birgit (2004). "Morphogenesis in the nematode-trapping fungus Arthrobotrys oligospora – an extensive plasticity of infection structures". Mycologist. 18: 125–133.
- ^ a b c d e f Degenkolb, Thomas; Vilcinskas, Andreas (2016). "Metabolites from nematophagus fungi and nematicidal natural products from fungi as an alternative for biological control. Part 1: metabolites from nematophagous ascomycetes". Applied Microbiology and Biotechnology. 100: 3799–3812.
- ^ Dreschler, Charles (1934). "Organs of Capture in Some Fungi Preying on Nematodes". Mycologia. 26: 140.