Pilobolus crystallinus

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Pilobolus crystallinus
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Scientific classification
Kingdom: Fungi Phylum: Zygomycota Class: Zygomycetes Order: Mucorales Family: Pilobolaceae Genus: Pilobolus Species: P. crystallinus
Binomial name
Pilobolus crystallinus var. crystallinus (F.H. Wigg.)Tode(1784)

Description and significance

The species Pilobolus crystallinus is a type of spore forming fungus that falls into the order of a mucor. According to Wikipedia two other common names for this fungus are the “Dung Cannon” or the “Hat Thrower”. This fungus begins its life cycle in the form of a sporangium that has been discharged onto some grass. Herbivorous animals which are animals that eat grass such as cows, horses, deer’s, etc. comes along and eat the grass with the sporangium sitting on it. The sporangium passes through the digestive tract of the animal without causing any harm to the animal and without germinating. It is excreted outside the host in the feces of the animal where it begins germination growing as mycelium. They grow 2-4 centimeters tall under surfaces where oxygen concentration is low because oxygen prevents radial growth of it hyphae. The pilobolus decays the feces of the animal using the nitrogen, water etc. found in the feces as its source of food. Once the nutrients in the feces are depleted the pilobolus shoots it sporangium away from the feces into a new set of grass where it will sit waiting again to be eaten by herbivorous animals so it can repeat the lifecycle. McVickar in 1942 and later Ootaki et al. in 1993 categorized the development of pilobolus crystallinus into six stages. In the first stage there is elongation of the sporangiophore at the apex without rotation. The second stage a sporangiophore develops into a sporangium. In the third stage no growth occurs and in the fourth stage a subsporangial vesice starts expanding under the sporangium. Stage five spore maturation occurs and the hypha region below the subsporangial vesicle elongates and in the last stage, stage six the subsporangial vesicle bursts open and the sporangium are releases into the air.

This is a time lapse video pilobolus crystallinus development which was documented by Dave Kalb and Kent Loeffler from Cornell University

[1]

Cell structure and metabolism

• Scanning and transmission electron microscope has been used in studying the structure of pilobolus crystallinus. The stalk which is a structure that resembles a plant stem is transparent and it rises above the feces. The stalk is always oriented towards the sunlight which increases the chances that the sporangium will land on a new set of grass once they have been dispersed. The subsporangial vesicle is a balloon like structure found at the end of the stalk. This vesicle fills with fluid and builds up a pressure called turgor pressure. Turgor pressure is the force that keeps the pilobolus upright and once the pressure builds up to 7 ATM or greater the pilobolus is able shoot its sporangium to a fresh set of grass up to 2 meters away which is 6 feet reaching speed of 0-45 mph during the first millimeter of travel. The subsporangial vesicle also serves the function as a lens focusing light towards the base of the vesicle through the carotenoid pigments. On top of the subsporangial vesicle there is one black sporangium which is the structure that produces and contains the spores. The spores within the sporangium are called sporangiospores and the sporangiospore is an asexual fruiting structure found in the pilobolus species of fungus. There are two different sizes of calcium oxalate crystals, some large and some small covering the surface of the sporangium. These crystals are hydrophobic so when the spores of the pilobolus are shot into the air the hydrophobic part is repelled by the dew on the grass causing the sporangium to flip over so that they land on their bottom which is sticky. The large crystals surround the spines with a central pore which serves as protection. The vesicle contains a mucus like substance which enables the spores that stick to grass it lands on. It travels through the digestive systems of animals and begins it growth in their feces.

Ecology

Pilobolus crystallinus is a corprophilous or dung loving fungi. It is a heterotrophic organism meaning it is not able to produce its own food and depends on the nutrients in the feces of herbivorous animals as its food source. The feces of herbivorous animals contains many nutrients which include undigested plant remains, large quantities of mostly dead bacteria, water soluble vitamins, growth factors, carbohydrates and mineral ions such as corpogens It has a high nitrogen content, high water content, broken down red blood cells and bile pigment. Pilobolus crystallinus produces exoenzymes to digest its food outside its body and then it absorbs the nutrients and although it does not utilize all these nutrients in the animal feces it is dependent on the nitrogen source found in the dung of animals as it food source. It also needs the water found in the feces of animals in order to disperse its spores. Pilobolus uses the corpogen in the feces for its growth and reproduction. Pilobolus crystallinus has some unique features to enhance its chances for survival. They have the ability to disperse their spores up to six feet away to a new food source since herbivorous animals do not eat near their feces. It has phototropic response which means the entire sporangium grows towards sunlight and the spores are launched only during the day. This determines the direction of the spores when they are dispersed and since grass grows in sunlight, this increases their chances that they will land on grass. The dark pigmentation of the spores protects them from being damaged by ultraviolet light. The spores vesicle has a sticky mucus that allows the spores to stick to vegetation. The spores does not germinate within the digestive tract of the herbivorous animals so they are able to with stand the high temperature and digestive enzymes of the gut. Nematodes has a symbiotic relationship with pilobolus crystallinus because they assist the fungi with decomposition of the animal feces but when the nutrients become depleted the nematodes larva usually sits on top of the fungi where it gets launched towards a new food source.

Pathology

Herbivorous animals such as deer’s, cattle, elk, horses’ etc. can become infected by parasitic organisms called lungworms. The larva of the lungworm is excreted in the feces of these animals. The larva can position themselves on the sporangiophores of philobolus crystillinus and it is launched with the sporangium where they now have the ability to infect a new host.

References

1)http://www.plantpath.cornell.edu/PhotoLab/TimeLapse2/Pilobolus1_credit_FC.html

2)http://en.wikipedia.org/wiki/Pilobolus_crystallinus

3)http://www.jstor.org/pss/3757932

4)http://bioweb.uwlax.edu/bio203/s2007/seidler_ashl

5)http://en.wikipedia.org/wiki/Pilobolus

6)http://www.accessexcellence.org/RC/CT/no_place_like_dung.php