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| ==Description and significance== | | ==Description and significance== |
| ''Pseudomonas putida'' are [[Gram-negative]] rod-shaped [[bacteria]]. They are classified as Group 1 in ''Pseudomona''. Other ''Pseudomonads'' are being re-evaluated to see if they truly fall into this category, while ''P. putida'' is firmly place in this group. ''P. putida'' are [[flourescent]], [[aerobic]], non sporeforming, oxidase positive bacteria. Having one or more polar [[flagella]], they are motile organisms. They can be found in moist environments, such as soil and water, and grow optimally at room temperature. Certain strains have the ability to grow on and break down many dangerous pollutants and aromatic [[hydrocarbons]] such as toluene, [[benzene]], and ethylbenzene. ''P. putida'' can also be used in petroleum plants to purify fuel. This bacterium is also capable of promoting plant growth after root colonization as well as simultaneously providing protection for the plant from pests and other harmful bacteria. | | ''Dicrocoelium dendriticum'' a small liver fluke, is a parasitic organism. That is, it benefits from its relationship to the host while contributing nothing to the survival of that host such that it may lower its host’s fitness. Theory and mechanisms on parasite manipulation of host fitness is a current topic of much controversy (see ‘Selfish Memes’ section below). |
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| ==Genome structure== | | ==Morphology== |
| The genome of ''Pseudomonas putida'' was sequenced due to the many unique abilities that this bacterium possesses. Scientists are interested in which genes cause what function. So far, ''P. putida'' has the most genes of any microorganism that break down chemicals such as aromatic [[hydrocarbons]]. Research is being done on the difference in genome of ''P. putida'' and its relative ''Pseudomonas aeruginosa'' in relation to cystic fibrosis. While ''P. aeruginosa'' infects and kills those with the disease, ''P. putida'' lacks the genes that causes such destruction, like the genes that code for enzymes that digest [[cell membrane]]s.
| | Dorso-ventrally flattned (lance shaped), adult lancet flukes are semi transparent ~8-14mm in length and ~2-3mm in width, oval shaped with the anterior slightly more narrow in shape compared to its posterior, both ends being slightly tapered (Citation 1, 2 ). At its tip the anterior contains an oral sucker. A hermaphrodite, the adult lancet fluke contains two lobed testes, in its anterior region, juxtaposed to its ovary, and the uterus lies below in its midsection. Vitellaria glands flank its reproductive organs, and are important in egg production. The digestive components (gut and bladder) lie in the posterior portion of its body (Citation 3). |
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| The Pseudomonas putida strain KT2440 [[genome]] was sequenced as a joint project between [[The Institute for Genomic Research]] and a German consortium in 1999. The way that they sequenced the genome was using the random shotgun method. They found that the one circular [[chromosome]] contains 6,181,863 base pairs. The total number of genes is 5,516, with 5,421 being [[protein]] coding. The total number of repeats, or stretches greater than 200 base pairs and almost identical, was 398. Interestingly, there was a high GC content in the genome, which created some difficulty in sequencing through the traditional methods. A significant amount of genes were found to code for enzymes that are used in the decomposition of matter. Most of the other genes are critical for Pseudomonas putida’s ability to recognize and react to external toxins and chemical signals. They also contain multiple accessory plasmids, including TOL and OCT plasmids, that aide the bacterium in breaking down environmental pollutants found in soil and water. Through sequencing the Pseudomonas putida genome, scientists were able to determine the biotechnological potential of the organism.<ref>[http://www1.qiagen.com/literature/Posters/PDF/DNA_isolation/1014161SPOS_SEQ_0400.pdf]</ref>
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| ==Cell structure and metabolism==
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| ''Pseudomonas putida'' are aerobic oxidase positive bacteria, with one or more flagella. They can be found in moist environments, such as soil and water, and grow at a temperature of 25-30 degrees Celcius. Although ''Pseudomonas putida'' does not form spores, they are still able to withstand harsh environmental conditions. It is able to resist the severe effects of organic solvents that pollute the surrounding soil. In response to changes in its chemical surroundings and to help with membrane fluidity and cellular uptake, it can alter the degree of fatty acid saturation and even undergo cis-trans isomerization. ''P. putida'' are unique saprobes in that use a wide variety of non-living material as their source of nutrition, including multiple types of aromatic [[hydrocarbons]]. This allows them to be agents of bioremediation, one of the most differentiating and impressive features of ''Pseudomonas putida''.
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| ==Ecology== | | ==Parasitic Reservoirs: inside and outside the Definitive Host == |
| ''Pseudomonas putida'' has an incomparable effect on the environment. They are able to protect plants from pests, promote plant growth, and clean up organic pollutants found in soil and water. | | ''Dicrocoelium dendriticum’s '' habitat includes lowland or mountain pastures, of dry and alkaline consistency, providing appropriate conditions for its definitive and intermediate hosts (Citations 1, 2, and 3). The adult lancet fluke necessarily inhabits the liver of its definitive host, specifically the bile ducts and gall bladder of domesticated and wild ruminating animals (sheep, goat and cattle). Although, they can also be found in the liver of dogs, rabbits, horses, humans and some rodents Citation 2. Endogenous host and environmental conditions are critical for its survival, whereby each intermediate host must be favored in the collective biotope, making it difficult to model similar conditions in the laboratory. Since its continuance into the liver of its definitive host for sexual reproduction is dependent on prior passage through two other distinct host organisms, conditions must favor each part of this biological community. Once an adult, it uses its hermaphroditic body plan to propagate itself several orders of magnitude, but to get their the fluke must be ingested by specific intermediate hosts, which allow it to carry out the different stages of its life cycle (Citation 2). |
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| The surface of the root and the soil that surrounds it are loaded with nutrients released by the plant. This environment is optimal for microbial growth. ''Pseudomonas putida'' is attracted to this area, and in turn promotes plant growth and even protects the root against pathogens. Two key elements that allow ''P. putida'' to attach in the first place is that they are motile and chemotactic towards the root output. After the initial attraction and migration toward the root, the bacteria immediately begins to grow and divide, forming multiple colonies around the root. The maximum population size is directly related to root weight, and once it is reached the number of colonies will stay constant. All of this can happen in less than 48 hours!
| | ==Life Cycle: A Definitive Host and Two Intermediate Hosts== |
| | | A trifecta of successful host:parasite adaptation, the small liver flukes’ life cycle and mode of transmission have been well described by the work of Krull and Mapes (citation 4). Collectively their work showed that infection of the definitive host is initiated by ingestion of infected ants and cannot be bypassed by eating the slimeballs of infected snails, the second intermediate hosts (Citation 3). Adult flukes in the bile ducts, lay dark brown eggs each containing a miracidium, which are expelled with the bile into the intestine and incorporated in the feces. These are viable embryos are only hatched upon ingestion by the appropriate species of snail, Cionella lubrica in North America (There are many other possible host snail species depending on geographical location i.e. In France Cochlicella acuta) Citation 2. The hatching mericidia penetrate the glandular intestinal epithelium and then undergo several rounds of asexual replication into daughter sporocycts Citation 1 and 2. These daughter sporocysts mature into motile larva, called mature cercariae and travel to the snails’ respiratory chambers, a process that can take 5 months depending on season or age of the snail Citation 2, and 3. The cercariae contain glands which are speculated to be involved in the formation of slimeballs. Several ~500-5000 cercariae are collected in these slime accumulations but little is known about the mechanism of their formation Citation 1, 2, and 3. Slimeballs stick to nearby plants and debris, each snail usually produces one but can produce more Citation 3. These slimeballs are ingested by a specific species of ant, in North America Formica fusca (Again, several species are capable of being intermediate host, differences being dependent on location). The larva then transform into metacercariae which grow in the abdomen of the ant. After a period of about a month (Citation 2) one or more may become localized in the subesophageal ganglion, which alters the normal neurological processes resulting in changes in normal behavior of the ant, when temperatures are low (Citation 1 ). In this parasite mediated hijacked state the ant climbs to the tips on blades of grass where they exposed to grazing mammals such as sheep, goats and cows Citation. Finally, the metacercariae are in the gut of the now infected definitive host where they are encysted in the duodenum (citation 2). The larva excyst and migrate to the bile ducts and then the gall bladder. In the bile ducts is where they will develop into cross fertilizing and hermaphroditic adult flukes, capable of releasing new eggs into the environment, in the host excrement Citations 1,2 and 3. |
| ''Pseudomonas putida'' play a huge role in bioremediation, or the removal or naturalization of soil or water contaminants. They can degrade toluene, xylene, and benzene, which are all toxic components of gasoline that leak into the soil by accidental spills. Other strains can convert styrene, better known as packing peanuts, which do not degrade naturally, into the biodegradable plastic polyhydroxyalkanoate (PHA). Methods used to get rid of styrene include incinerating it, spreading it on land, and injecting it underground, all of which release the toxins into the environment. Styrene can cause muscle weakness, lung irritation, and may even effect the brain and nervous system. Due to the fact that ''P. putida'' can use styrene as its only source of carbon and energy, it can completely remove this toxic chemical. ''P. putida'' can also turn Atrizine, an herbicide that is toxic to wildlife, into [[carbon dioxide]] and [[water]].
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| ==Pathology== | | ==Pathology== |
| In genetic terms, ''Pseudomonas putida'' is very similar to strains of ''[[Pseudomonas aeruginosa]]'', an opportunistic human pathogen. Although there is a considerable amount of genome conservation, ''P. putida'' seems to be missing the key virulent segments that ''P. aeroginosa'' has. Being a non-pathogenic bacteria, there has been only a handful of episodes where ''P. putida'' has infected humans. For the most part, it has been with immunocompromised patients, causing septicaemia, [[pneumonia]], urinary tract infections, nosocomial bacteremia, septic [[arthritis]], or [[peritonitis]]. ''P. putida'' is also closely related to ''[[Pseudomonas syringae]]'', an abundant plant pathogen, but again it lacks the gene that causes such disease.
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| Several cases of disease caused by ''Pseudomonas putida'' have been investigated, being that the bacterium rarely colonizes mucosal surfaces or skin. One case was a 43-year-old female who was receiving nightly [[peritoneal dialysis]] treatments following a laparoscopic ovarian cyst operation. She developed [[peritonitis]] due to infection by ''Pseudomonas putida''. Through this case and others, it was determined that risk factors for developing such an infection include the insertion of [[catheters]], intubation, and/or intravascular devices following a recent course in [[antibiotics]]. <ref>[http://www.springerlink.com/content/278654l42x54x7k7/ Dervisoglue, E., Dundar, D.O., Yegenaga, I., Willke, A. “Peritonitis due to ''Pseudomonas putida'' in a Patient Receiving Automated Peritoneal Dialysis”. ''Infection''. 2007.]</ref>
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| Another case of ''Pseudomonas putida'' infection was found in ten patients in and ear, nose, and throat outpatient clinic during the summer of 2000. All ten patients had chronic [[sinusitis]], making them more susceptible to infection due to their challenged immune systems. Through investigation, it was discovered that all of the patients shared the same examination room. The source of the bacteria was from a contaminated bottle of StaKleer found in that room. StaKleer is an anti-fog solution used on mirrors and endoscopes to prevent condensation from occurring, allowing for the proper visualization of tissues. Other unopened bottles of the solution at the clinic were found to be contaminated with ''Pseudomonas putida'' as well.<ref>[http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/00vol26/dr2621eb.html Romney, M., Sherlock, C., Stephens ,G., Clarke, A.. “Pseudo-outbreak of ''Pseudomonas Putida'' in a Hospital Outpatient Clinic Originating from a Contaminated Commercial Anti-Fog Solution”. ''Canada Communicable Disease Report''. November, 2000. Vol. 26-21.]</ref>
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| ==Application to Biotechnology==
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| ''Pseudomonas putida'' is being used in conjunction with ''[[Escherichia coli]]'' for developing new drugs. This study focuses on [[myxochromide S]], a compound produced by ''Stigmatella aurantiaca'', but the method is revolutionary in that there is unprecedented expression of gene clusters. The beginnings of many new drugs are from natural sources, such as plants and microorganisms, but they are too expensive to harvest from the origin. [[Combinatorial biosynthesis]] has revolutionized drug development by allowing the structure of certain molecules to be changed within an organism. With this metabolic engineering, where genes are introduced and their expressions are tightly controlled, successful production of drugs is possible. ''Pseudomonas putida'' is unique in that it allows the expression of a large biosynthetic cluster, producing five times as much myxochromide S as ''Stigmatella aurantiaca''. This will also permit scientists to connect multiple clusters of genes onto a single DNA fragment. <ref>[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRP-4FSV963-2&_user=699469&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000039278&_version=1&_urlVersion=0&_userid=699469&md5=0ae4bd35a20dd7aa05af430f4da09784 Bechthold, A. “Exploiting ''Pseudomonas putida'' for Drug Development”. ''Chemistry & Biology''. March, 2005. Vol. 12, Issue 3. p. 261]</ref>
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| ''Pseudomonas putida'' is able to purify [[fuel]], a capability that the petroleum industry has taken great interest in. As previously mentioned, ''P. putida'' is able to convert [[styrene]], a toxic waste product, into a biodegradable plastic. The strain [[CA-3]] turns styrene into a stored energy source, in the form of a plastic [[polymer]] called [[polyhydroxyalkanoate]] (PHA). Using styrene its only source of carbon and energy, the styrene is completely used up, creating an elastic type of polymer. This polymer can then be used in the production of drug carriers, plastic coating of cardboard, and medical implants.
| | ==Evolutionary Significance== |
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| ==Current Research== | | ==Current Research== |
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| ==== "Benzene, Toluene, and Xylene Biodegradation by ''Pseudomonas putida'' CCMI 852"==== | | ==== ==== |
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| [[Gasoline]] spills create a large amount of toxic pollution in the environment, being that the major components are benzene, toluene and xylene isomers. Catalogued by the [[U.S Environmental Protection Agency]] as “priority pollutants”, gasoline is a main cause of water well and spring contamination. ''Pseudomonas putida'' can successfully degrade these dangerous components of gasoline, and can aide in the cleanup of such pollutants. This article discusses the research being done in order to determine what environment and mixture of compounds will allow for the most degradation. The [[metabolic]] pathway that ''P. putida'' uses to break down these compounds is investigated. The [[TOL]] pathway does not utilize benzene as a substrate, while the [[TOD]] pathway does. Various combinations of these elements of gasoline were used during experimentation. Maximum degradation occurred when each compound was alone in solution. Once any other compound was introduced, the rate automatically dropped, but it dropped most drastically when benzene was introduced. Toluene was degraded at a rate twice as fast as xylene. Benzene concentration always remained unchanged, when alone or in a mixture. It is then obvious that ''P. putida'' did not degrade benzene, even when no other compounds were present. It is suggested that this ''P. putida CCMI 852'' strain contains a TOL plasmid, therefore preventing the degradation of benzene. <ref>[http://www.scielo.br/pdf/bjm/v36n3/arq10.pdf Otenio, M.H., Da Silva, M.T.L., Marques, M.L.O, Roseiro, J.C., Bidoia, E.D. “Benzene, Toluene, and Xylene Biodegradation by ''Pseudomonas putida'' CCMI 852”. ''Brazilian Journal of Microbiology''. 2005. P. 258-261.]</ref>
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| ==== "Diversity and activity of biosurfactant-producing ''Pseudomonas'' in the rhizosphere of black pepper in Vietnam"====
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| [[Black pepper]], a major crop and source of income for the country of [[Vietnam]], is also the most important spice crop in the world. This ‘King of Spices’ is particularly susceptible to the pathogen ''[[Phytophthora capsici]]'', which eats away at the roots of the plant and causes death and disease. It can potentially cause up to 40-50% of crop death, and in Vietnam an annual loss of around 20%. ''Pseudomonas putida'' was found to produce [[biosurfactant]]s, which disrupt the membrane of the ''Phy. Capsici'' zoospores, causing death within minutes. Using ''P. putida'' as a method for controlling ''Phy. Capsici'' will be more effective than using pure biosurfactants created in a lab. One reason for this is that the chemical form may not be delivered efficiently to the roots, because they must fully penetrate the soil to the level of the rhizosphere. ''P. putida'' is chemotactic towards root output, and move via flagella directly toward the root, subsequently creating secure colonies. Using ''P. putida'' as a [[pesticide]] will also be a long-lasting form of treatment, because the colonies not will get washed away by a rainstorm like the chemical form could.
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| [[Rhizosphere]] samples were taken from three different districts in Vietnam, and various testing was done with different biosurfactanct producing organisms and bacteria. ''P. putida'' provided a significant amount of prevention of plant wilt, providing adequate protection from ''Phy. capsici''. This was greater then when contrasted with other bacteria tested, such as ''[[Bacillus spp.]]'', ''[[Trichoderma harzianum]]'', and ''[[P. flourescens]]''. When ''P. putida'' was introduced to plant root when no pathogen was present, there were more interesting results. This bacterium had considerably increased shoot height and weight, and also raised the number of roots grown. More research is being done in the area, as it further development of this idea will help control plant pathogens. <ref>[http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2672.2007.03618.x Tran, H., Kruijt, M., Raaijmakers, J.M. “Diversity and Activity of Biosurfactant-producing ''Pseudomonas'' in the Rhizosphere of Black Pepper in Vietnam”. ''Journal of Applied Microbiology''. March, 2008. Vol. 104. p. 839-851.]</ref>
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| ==== "Accumulation of Polyhydroxyalkanoate from Styrene and Phenylacetic Acid by ''Pseudomonas putida'' CA-3" ====
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| ''Pseudomonas putida'' has the unique ability to transform a toxic pollutant into a biodegradable plastic. Over 25 million kilograms of [[styrene]], a compound that can cause respiratory tract infection, muscle weakness, and narcosis, is released into the environment every year in the U.S. alone. The product, [[polyhydroxyalkanoate]], can be used as synthons for certain [[antibiotics]], [[vitamins]], and anti-cancer drugs. They are also used in other areas of medical applications such as tissue engineering and wound management. The pathway and mechanism for this transformation is investigated, where [[aromatic]] hydrocarbons are transformed into [[aliphatic]] PHA. During the growth cycle, there is the strict use of carbon and nitrogen with styrene, glucose, and phenylacetic acid by ''P. putida'' as the carbon and energy source. The effects of altering the carbon to nitrogen ratio and level are tested in relation to the accumulation of the product PHA.
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| The study showed that when nitrogen levels dropped, PHA production began. The effect of carbon supply was studied as well, and only when carbon to nitrogen ratios of 9:1 for cells on glucose, 10:1 for cells on phenylacetic acid, and 14:1 for cells grown on styrene were reached did PHA begin to accumulate. Next, nitrogen was manipulated while carbon was held constant, showing that the highest PHA content was found when nitrogen concentration was the lowest.
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| The manner in which styrene is converted to PHA is through [[fatty acid de novo biosynthesis]], which is catalyzed by [[3-hydroxy-acyl-ACP:CoA transacylase]]. The plastic polymer has a destruction point of 265 degrees Celcius, and a uniquely low molecular weight and high [[polydispersity]]. This is also the first time that an aromatic substrate is converted into aliphatic PHA. Further research will be done to investigate ways to increase PHA yield from styrene using ''P. putida''.<ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1082534 Ward, Patrick G., de Roo, Guy, O’Connor, Kevin E. “Accumulation of Polyhydroxyalkanoate from Styrene and Phenylacetic Acid by ''Pseudomonas putida'' CA-3”. ''Applied and Environmental Microbiology''. April, 2005. Vol. 71. p. 2046-2052.]</ref>
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| ==References== | | ==References== |
| | | References |
| [1]↑[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRP-4FSV963-2&_user=699469&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000039278&_version=1&_urlVersion=0&_userid=699469&md5=0ae4bd35a20dd7aa05af430f4da09784 Bechthold, A. “Exploiting ''Pseudomonas putida'' for Drug Development”. ''Chemistry & Biology''. March, 2005. Vol. 12, Issue 3. p. 261]
| | 1. Otranto, Domenic Dicrocoeliosis of ruminants: a little known fluke disease |
| | | 2. Desmond, James introduction to animal parisitology p. 214 Figure 14.14 |
| [2]↑[http://www.springerlink.com/content/278654l42x54x7k7/ Dervisoglue, E., Dundar, D.O., Yegenaga, I., Willke, A. “Peritonitis due to ''Pseudomonas putida'' in a Patient Receiving Automated Peritoneal Dialysis”. ''Infection''. 2007.]
| | 3. Krull, W. H., and C. R. Mapes. "Studies on the biology of Dicrocoelium dendriticum (Rudolphi, 1819) Looss, 1899 (Trematoda: Dicrocoeliidae), including its relation to the intermediate host, Cionella lubrica II. Collection of the snail, Cionella lubrica, and its maintenance in the laboratory." Cornell Vet 41 (1951): 433-44. |
| | | ==Links== |
| [3]↑[http://www.scielo.br/pdf/bjm/v36n3/arq10.pdf Otenio, M.H., Da Silva, M.T.L., Marques, M.L.O, Roseiro, J.C., Bidoia, E.D. “Benzene, Toluene, and Xylene Biodegradation by ''Pseudomonas putida'' CCMI 852”. ''Brazilian Journal of Microbiology''. 2005. P. 258-261.]
| | 1. http://www.fao.org/wairdocs/ILRI/x5492E/x5492e04.htm |
| | | 2. http://www.weichtiere.at/Mollusks/Schnecken/parasitismus/dicrocoelium.html |
| [4]↑[http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/00vol26/dr2621eb.html Romney, M., Sherlock, C., Stephens ,G., Clarke, A.. “Pseudo-outbreak of ''Pseudomonas Putida'' in a Hospital Outpatient Clinic Originating from a Contaminated Commercial Anti-Fog Solution”. ''Canada Communicable Disease Report''. November, 2000. Vol. 26-21.]
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| [5]↑[http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2672.2007.03618.x Tran, H., Kruijt, M., Raaijmakers, J.M. “Diversity and Activity of Biosurfactant-producing ''Pseudomonas'' in the Rhizosphere of Black Pepper in Vietnam”. ''Journal of Applied Microbiology''. March, 2008. Vol. 104. p. 839-851.]
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| [6]↑[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1082534 Ward, Patrick G., de Roo, Guy, O’Connor, Kevin E. “Accumulation of Polyhydroxyalkanoate from Styrene and Phenylacetic Acid by ''Pseudomonas putida'' CA-3”. ''Applied and Environmental Microbiology''. April, 2005. Vol. 71. p. 2046-2052.]
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| [7]↑[http://www1.qiagen.com/literature/Posters/PDF/DNA_isolation/1014161SPOS_SEQ_0400.pdf| DNA isolation, from Qiagen]
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| [8]↑[http://microbewiki.kenyon.edu/index.php/Pseudomonas_putida]
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| Dicrocoelium dendriticum
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| Scientific classification
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| Kingdom:
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Animalia
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| Phylum:
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Platyhelminthes
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| Class:
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Trematoda
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| Order:
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Plagiorchiida
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| Family:
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Dicrocoeliidae
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| Genus:
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Dicrocoelium
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| Species:
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D. dendriticum
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| Binomial name
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Dicrocoelium dendriticum
Rudolphi, 1819
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Description and significance
Dicrocoelium dendriticum a small liver fluke, is a parasitic organism. That is, it benefits from its relationship to the host while contributing nothing to the survival of that host such that it may lower its host’s fitness. Theory and mechanisms on parasite manipulation of host fitness is a current topic of much controversy (see ‘Selfish Memes’ section below).
Morphology
Dorso-ventrally flattned (lance shaped), adult lancet flukes are semi transparent ~8-14mm in length and ~2-3mm in width, oval shaped with the anterior slightly more narrow in shape compared to its posterior, both ends being slightly tapered (Citation 1, 2 ). At its tip the anterior contains an oral sucker. A hermaphrodite, the adult lancet fluke contains two lobed testes, in its anterior region, juxtaposed to its ovary, and the uterus lies below in its midsection. Vitellaria glands flank its reproductive organs, and are important in egg production. The digestive components (gut and bladder) lie in the posterior portion of its body (Citation 3).
Parasitic Reservoirs: inside and outside the Definitive Host
Dicrocoelium dendriticum’s habitat includes lowland or mountain pastures, of dry and alkaline consistency, providing appropriate conditions for its definitive and intermediate hosts (Citations 1, 2, and 3). The adult lancet fluke necessarily inhabits the liver of its definitive host, specifically the bile ducts and gall bladder of domesticated and wild ruminating animals (sheep, goat and cattle). Although, they can also be found in the liver of dogs, rabbits, horses, humans and some rodents Citation 2. Endogenous host and environmental conditions are critical for its survival, whereby each intermediate host must be favored in the collective biotope, making it difficult to model similar conditions in the laboratory. Since its continuance into the liver of its definitive host for sexual reproduction is dependent on prior passage through two other distinct host organisms, conditions must favor each part of this biological community. Once an adult, it uses its hermaphroditic body plan to propagate itself several orders of magnitude, but to get their the fluke must be ingested by specific intermediate hosts, which allow it to carry out the different stages of its life cycle (Citation 2).
Life Cycle: A Definitive Host and Two Intermediate Hosts
A trifecta of successful host:parasite adaptation, the small liver flukes’ life cycle and mode of transmission have been well described by the work of Krull and Mapes (citation 4). Collectively their work showed that infection of the definitive host is initiated by ingestion of infected ants and cannot be bypassed by eating the slimeballs of infected snails, the second intermediate hosts (Citation 3). Adult flukes in the bile ducts, lay dark brown eggs each containing a miracidium, which are expelled with the bile into the intestine and incorporated in the feces. These are viable embryos are only hatched upon ingestion by the appropriate species of snail, Cionella lubrica in North America (There are many other possible host snail species depending on geographical location i.e. In France Cochlicella acuta) Citation 2. The hatching mericidia penetrate the glandular intestinal epithelium and then undergo several rounds of asexual replication into daughter sporocycts Citation 1 and 2. These daughter sporocysts mature into motile larva, called mature cercariae and travel to the snails’ respiratory chambers, a process that can take 5 months depending on season or age of the snail Citation 2, and 3. The cercariae contain glands which are speculated to be involved in the formation of slimeballs. Several ~500-5000 cercariae are collected in these slime accumulations but little is known about the mechanism of their formation Citation 1, 2, and 3. Slimeballs stick to nearby plants and debris, each snail usually produces one but can produce more Citation 3. These slimeballs are ingested by a specific species of ant, in North America Formica fusca (Again, several species are capable of being intermediate host, differences being dependent on location). The larva then transform into metacercariae which grow in the abdomen of the ant. After a period of about a month (Citation 2) one or more may become localized in the subesophageal ganglion, which alters the normal neurological processes resulting in changes in normal behavior of the ant, when temperatures are low (Citation 1 ). In this parasite mediated hijacked state the ant climbs to the tips on blades of grass where they exposed to grazing mammals such as sheep, goats and cows Citation. Finally, the metacercariae are in the gut of the now infected definitive host where they are encysted in the duodenum (citation 2). The larva excyst and migrate to the bile ducts and then the gall bladder. In the bile ducts is where they will develop into cross fertilizing and hermaphroditic adult flukes, capable of releasing new eggs into the environment, in the host excrement Citations 1,2 and 3.
Pathology
Evolutionary Significance
Current Research
References
References
1. Otranto, Domenic Dicrocoeliosis of ruminants: a little known fluke disease
2. Desmond, James introduction to animal parisitology p. 214 Figure 14.14
3. Krull, W. H., and C. R. Mapes. "Studies on the biology of Dicrocoelium dendriticum (Rudolphi, 1819) Looss, 1899 (Trematoda: Dicrocoeliidae), including its relation to the intermediate host, Cionella lubrica II. Collection of the snail, Cionella lubrica, and its maintenance in the laboratory." Cornell Vet 41 (1951): 433-44.
Links
1. http://www.fao.org/wairdocs/ILRI/x5492E/x5492e04.htm
2. http://www.weichtiere.at/Mollusks/Schnecken/parasitismus/dicrocoelium.html
