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Spontaneous human combustion
From Wikipedia, the free encyclopedia
For combustion not involving the human body, see spontaneous combustion.Spontaneous human combustion (SHC) is a term encompassing reported cases of the combustion of a living (or very recently deceased) human body without an apparent external source of ignition. In addition to reported cases, examples of SHC appear in literature, and both types have been observed to share common characteristics regarding circumstances and remains of the victim.
Forensic investigations have attempted to analyze reported instances of SHC and have resulted in hypotheses regarding potential causes and mechanisms, including victim behavior and habits, alcohol consumption and proximity to potential sources of ignition, as well as the behavior of fires that consume melted fats. Natural explanations, as well as unverified natural phenomena, have been proposed to explain reports of SHC. Current scientific consensus is that most, and conjectures perhaps all, cases of SHC involve overlooked external sources of ignition.
Overview"Spontaneous human combustion" refers to the death from a fire originating without an apparent external source of ignition; the fire is believed to start within the body of the victim. This idea and the term 'spontaneous human combustion' were first both proposed in 1746 by Paul Rolli in an article published in the Philosophical Transactions. Writing in the British Medical Journal, coroner Gavin Thurston describes the phenomenon as having "attracted the attention not only of the medical profession but of the laity" as early as 1834 (more than one hundred years prior to Thurston's 1938 article). In his 1995 book Ablaze!, Larry E. Arnold wrote that there had been about 200 cited reports of spontaneous human combustion worldwide over a period of around 300 years.
CharacteristicsThe topic received coverage in the British Medical Journal in 1938. An article by L. A. Parry cited an 1823-published book Medical Jurisprudence, which stated that commonalities among recorded cases of spontaneous human combustion included the following characteristics:
"[...]the recorded cases have these things in common:Alcoholism is a common theme in early SHC literary references, in part because some Victorian era physicians and writers believed spontaneous human combustion was the result of alcoholism.
- the victims are chronic alcoholics;
- they are usually elderly females;
- the body has not burned spontaneously, but some lighted substance has come into contact with it;
- the hands and feet usually fall off;
- the fire has caused very little damage to combustible things in contact with the body;
- the combustion of the body has left a residue of greasy and fetid ashes, very offensive in odour."
Forensic investigationAn extensive two-year research project, involving thirty historical cases of alleged SHC, was conducted in 1984 by science investigator Joe Nickell and forensic analyst John F. Fischer. Their lengthy, two-part report was published in the journal of the International Association of Arson Investigators,:3–11 as well as part of a book. Nickell has written frequently on the subject, appeared on television documentaries, conducted additional research, and lectured at the New York State Academy of Fire Science at Montour Falls, New York, as a guest instructor.
Nickell and Fischer's investigation, which looked at cases in the 18th, 19th and 20th centuries, showed that the burned bodies were near plausible sources for the ignition: candles, lamps, fireplaces, and so on. Sometimes these sources were left out of popular accounts of the alleged phenomenon while they were hyped as mysterious. The investigations also found that there was a correlation between alleged SHC deaths and victim's drunkenness or other incapacitation that could have caused them to be careless with fire and less able to respond properly to an accident. Where the destruction of the body was not extensive, the significant fuel source was the victim's clothing.
However, where the destruction was extensive, additional fuel sources were involved, such as chair stuffing, floor coverings, the flooring itself, and the like. The investigators described how such materials helped retain melted fat to burn and destroy more of the body, yielding still more liquified fat, in a cyclic process known as the "wick effect" or the "candle effect".
According to Nickell and Fischer's investigation, nearby objects often went undamaged because fire tends to burn upward, and it burns laterally with some difficulty. The fires in question are relatively small, achieving considerable destruction by the wick effect, and relatively nearby objects may not be close enough to catch fire themselves (much as one can get rather close to a modest campfire without burning). As with other mysteries, Nickell and Fischer cautioned against "single, simplistic explanation for all unusual burning deaths" but rather urged investigating "on an individual basis".:169
Suggested explanationsSome hypotheses attempt to explain how SHC might occur without an external flame source, while other hypotheses suggest incidents that might appear as spontaneous combustion actually had an external source of ignition – and that the likelihood of spontaneous human combustion without an external ignition source is quite low. Benjamin Radford, science writer and deputy editor of the science magazine Skeptical Inquirer, casts doubt on the plausibility of spontaneous human combustion, "If SHC is a real phenomenon (and not the result of an elderly or infirm person being too close to a flame source), why doesn't it happen more often? There are 5 billion [The world's population reached 5 billion in 1987] people in the world, and yet we don't see reports of people bursting into flame while walking down the street, attending football games, or sipping a coffee at a local Starbucks." Paranormal researcher Brian Dunning states that SHC stories "are simply the rare cases where a natural death in isolation has been followed by a slow combustion from some nearby source of ignition." He further suggested that reports of people suddenly aflame should be called "Unsolved deaths by fire", stating that an unknown cause did not necessarily imply that the fire lacked an external ignition source.
- Almost all cases of SHC involve persons with low mobility due to advanced age or obesity, along with poor health. Victims show a high likelihood of having died in their sleep, or of being unable to move once they had caught fire.
- Cigarettes are often seen as the source of fire, as the improper disposal of smoking materials causes one of every four fire deaths in the United States. Natural causes such as heart attacks may lead to the victim dying, subsequently dropping the cigarette, which after a period of smouldering can ignite the victim's clothes.
- The "wick effect" hypothesis suggests that a small external flame source, such as a burning cigarette, chars the clothing of the victim at a location, splitting the skin and releasing subcutaneous fat, which is in turn absorbed into the burned clothing, acting as a wick. This combustion can continue for as long as the fuel is available. This hypothesis has been successfully tested with animal tissue (pig) and is consistent with evidence recovered from cases of human combustion. The human body typically has enough stored energy in fat and other chemical stores to fully combust the body; even lean people have several pounds of fat in their tissues. This fat, once heated by the burning clothing, wicks into the clothing much as candle wax (which typically was originally made of animal fat) wicks into a lit candle wick to provide the fuel needed to keep the wick burning. The protein in the body also burns, but provides less energy than fat, with the water in the body being the main impediment to combustion. However, slow combustion, lasting hours, gives the water time to evaporate slowly. In an enclosed area, such as a house, this moisture will recondense nearby, such as on windows. Note that feet often have the least fat, so don't typically burn. (Hands also have little fat, but may burn if on the abdomen, which provides all the needed fat.)
- John Abrahamson suggested that ball lightning could account for spontaneous human combustion. "This is circumstantial only, but the charring of human limbs seen in a number of ball lightning cases are very suggestive that this mechanism may also have occurred where people have had limbs combusted," says Abrahamson.
- Scalding can cause burn-like injuries, including death, without setting fire to clothing. Although not applicable in cases where the body is charred and burnt, this has been suggested as a cause in at least one claimed SHC-like event.
- Brian J. Ford has suggested that ketosis, possibly caused by alcoholism or low-carb dieting, produces acetone, which is highly flammable and could therefore lead to apparently spontaneous combustion.
- SHC can be confused with Self immolation as a form of suicide. In the West self immolation accounts for 1% of suicides  while Radford claims in developing countries the figure can be as high as 40%
- Sometimes there are reasonable explanations for the deaths, but proponents ignore official autopsies and contradictory evidence, in favor of anecdotal accounts and personal testimonies.
Unverified natural phenomena
- Larry E. Arnold in his 1995 book Ablaze! proposed a pseudoscientific new subatomic particle, which he called "pyrotron".:99–106 Arnold also wrote that the flammability of a human body could be increased by certain circumstances, like increased alcohol in the blood.:84 He also wrote that extreme stress could be the trigger that starts many combustions.:163 This process may use no external oxygen to spread throughout the body, since it may not be an "oxidation-reduction" reaction; however, no reaction mechanism has been proposed. Researcher Joe Nickell has criticized Arnold's hypotheses as based on selective evidence and argument from ignorance.
- In his 1976 book Fire From Heaven, UK writer Michael Harrison suggests that SHC is connected to poltergeist activity because, he argues "the force which activates the 'poltergeist' originates in, and is supplied by, a human being". Within the concluding summary, Harrison writes: "SHC, fatal or non-fatal, belongs to the extensive range of poltergeist phenomena."
Notable examplesHenry Thomas, a 73-year-old man, was found burned to death in the living room of his council house on the Rassau estate in Ebbw Vale, South Wales, in 1980. His entire body was incinerated, leaving only his skull and a portion of each leg below the knee. The feet and legs were still clothed in socks and trousers. Half of the chair in which he had been sitting was also destroyed. Police forensic officers decided that the incineration of Thomas was due to the wick effect. His death was ruled 'death by burning', as he had plainly inhaled the contents of his own combustion.
In December 2010, the death of Michael Faherty in County Galway, Ireland, was recorded as "spontaneous combustion" by the coroner. The doctor, Ciaran McLoughlin, made this statement at the inquiry into the death: "This fire was thoroughly investigated and I'm left with the conclusion that this fits into the category of spontaneous human combustion, for which there is no adequate explanation."
Debunked examplesIn August 2013, Rahul, a two and one half months-old infant from Tamil Nadu, India, was admitted to the Kilpauk Medical College and Hospital in Chennai, having four reported burn injuries since birth. Initial tests ruled out any abnormalities, and further results led the hospital to conclude that it was not spontaneous human combustion. The baby's mother used to live in another village which had come in the news in 2004, when residents had complained that their homes spontaneously burst into flames. Investigations had shown that phosphorus hidden in cow dung had been present in the huts; phosphorus has a low ignition point and can cause fires.
In January 2015, Jayaramachandran, Rahul's younger brother, suffered 10% burns, claimed to be due to spontaneous combustion. However, doctors at Kilpauk Medical College Hospital have reported the claims as suspicious. When interviewed about the cases, the physician who treated the older brother in 2013 stated that "[t]here is no such thing as spontaneous human combustion. When Rahul was admitted to the hospital last year we clearly told the parents that it looked like someone was deliberately setting the infant on fire."
|This article appears to contain trivial, minor, or unrelated references to popular culture. Please reorganize this content to explain the subject's impact on popular culture rather than simply listing appearances; add references to reliable sources if possible, otherwise delete it. (April 2016)|
- The first chapter of Frederick Marryat's book Jacob Faithful (1834) describes the spontaneous combustion of Jacob's mother.
- In their 2004 book "Brimstone", Preston and Child used Spontaneous Human Combustion (YAY) as the initial possible explanation for a series of unsolved murders.
- In the comic story "The Glenmutchkin Railway" (1845) by J.E. Aytoun, one of the railway directors, Sir Polloxfen Tremens, is said to have died of spontaneous combustion.
- Herman Melville's 1849 novel Redburn describes the spontaneous combustion of a sailor.
- In Charles Dickens' 1853 novel Bleak House, the character Mr. Krook, an alcoholic landlord, combusts spontaneously due to excessive alcohol in his body. In his preface to the novel, Dickens gives examples of other reported cases.
- According to a March 2013 BBC feature, it has been suggested[attribution needed] that the Book of Numbers contains a reference to spontaneous human combustion, but that "their accuracy may be disputed as these accounts are much too old and based on second-hand knowledge to be considered reliable evidence."
- In an episode of The X-Files titled "Trevor", Dana Scully examines charred human remains and hypothesizes that the victim might have succumbed to spontaneous human combustion.
- The South Park episode "Spontaneous Combustion" deals with Kenny McCormick dying from spontaneous combustion.
- In an episode of CSI: Crime Scene Investigation entitled "Face Lift", Sara Sidle and Warrick Brown investigate the case of a woman who was incinerated in her easy chair, leading Sidle to suspect spontaneous human combustion. The CSI episode "The Theory of Everything" also explores the case of a man who spontaneously combusts after a police officer douses him with pepper spray and shoots him with a stun gun, until it is discovered he was doused with pepper spray that contained alcohol; the effect was repeated and deemed "plausible" on MythBusters, whose hosts were also guest stars in the CSI episode.
- Several installments of the popular video game series The Sims implement spontaneous combustion as a cause of death. The chances of experiencing this are very low, approaching 0.1%.
- In the 1984 film This Is Spinal Tap, one of the band's former drummers dies from spontaneous combustion. David St. Hubbins comments that "Dozens of people spontaneously combust each year. It's just not really widely reported."
- The fifth episode of the sci-fi comedy Red Dwarf, titled "Confidence and Paranoia", includes a visual representation of the spontaneous combustion of the Mayor of Warsaw in 1546 as a hallucination by one of the crew members.
- In the manga/anime series Rurouni Kenshin, the character Shishio Makoto, one of the main antagonists, dies from spontaneous combustion as a result of over-exertion from fighting and a lack of sweat glands.
- In Season 7 Episode 3 of ER ("Mars Attacks"), a patient who complains of spontaneous human combustion is found on fire by Drs. Weaver and Finch.
- The video game Parasite Eve deals with the main character investigating a mass-spontaneous combustion during an opera at Carnegie Hall.
- In the TV series Picket Fences, a town mayor dies from spontaneous combustion.
- In an episode of the TV series The Young Indiana Jones Chronicles ("Transylvania, January 1918"), a character dies from spontaneous combustion, with only his charred feet remaining intact.
- In Season 2 Episode 10 of the TV series Dead Like Me ("Death Defying"), a reaper target dies by spontaneous combustion.
- In the book Si Janus Silang at ang Tiyanak ng Tabon, characters alleged to have died from spontaneous human combustion are discovered to have been killed by supernatural phenomenon.
- Within the work of the fiction writing group, the SCP Foundation, most cases of SHC are caused by the effects of SCP-081, a virus that was discovered and contained by the eponymous organization.
- In the TV series Bones Season 5 Episode 8 ("The Foot in the Foreclosure"), when tour of a house - ashes are found on a bed, only remains of one foot was left.
- In Season 2 Episode 8 "Heart Break" of NCIS, spontaneous combustion is suspected by Abby. This theory is debunked as the resulting combustion was rigged by the Doctor to cover up the failing of a valve she had repaired instead of replacing in a heart surgery. The combustion occurred by filling his chest cavity with oxygen after he suffered cardiac arrest and then igniting via letting a cigarette slow burn into a match book to spark the ignition.
- The Series 4 finale of New Tricks features a body being reduced to a smoldering pair of feet. Several members of UCOS claim it to be spontaneous combustion, inspiring Brian to disprove the myth. He successfully demonstrates the "Wick effect" using a dead pig dressed in the same attire as the victim, thereby explaining how the body was disposed of after the murder.
- In Kevin Wilson's 2009 short story collection Tunneling to the Center of the Earth (Ecco/HarperCollins), the story "Blowing Up on the Spot" chronicles the life of a young man afraid of his own SHC after his parents spontaneously combust.
- Death by burning
- Exploding animal
- Fan death
- List of paranormal magazines
- Rolli, Paul (1746). "An Extract, by Mr. Paul Rolli, F.R.S. of an Italian Treatise, written by the Reverend Joseph Bianchini, a Prebend in the City of Verona; upon the Death of the Countess Cornelia Zangari & Bandi, of Cesena" (476). Philosophical Transactions: 447.
- Thurston, Gavin (18 June 1938). "Spontaneous Human Combustion". British Medical Journal 1 (4041): 1340. doi:10.1136/bmj.1.4041.1340-a. PMC 2086726.
- Arnold, Larry E. (1995). Ablaze!: The Mysterious Fires of Spontaneous Human Combustion. ISBN 0871317893.
- A Treatise on Medical Jurisprudence, by Dr John Ayrton Paris M.D. and John Samuel Martin Fonblanqueire Barister at Law, 3 Vols, London, 1823
- Parry, L. A. (4 June 1938). "Spontaneous Combustion". British Medical Journal 1 (4039): 1237. doi:10.1136/bmj.1.4039.1237-b. PMC 2086687.
- Collins, Nick (23 September 2011). "Spontaneous human combustion: examples from fiction". The Telegraph. Retrieved 2013-10-10.
- Nickell, Joe; Fischer, John F. (March 1984). "Spontaneous Human Combustion". The Fire and Arson Investigator 34 (3).
- Nickell, Joe (1991). Secrets of the Supernatural. Amherst, NY: Prometheus Books. pp. 149–157, 161–171.
- "Skeptic's Dictionary on spontaneous human combustion, Retrieved Oct 20, 2007 "The physical possibilities of spontaneous human combustion are remote."". Skepdic.com. 24 September 2011. Retrieved 24 May 2012.
- "Irishman died of spontaneous human combustion, coroner claims". MSNBC. 26 September 2011. Retrieved 8 October 2011.
- Brian Dunning (17 May 2011). "Spontaneous Human Combustion: People can catch on fire... but can it really happen when there is no external source of ignition?". Skeptoid: Critical Analysis of Pop Phenomena. Retrieved 7 November 2011.
- "Spontaneous Human Combustion". Skeptoid.com. Retrieved 24 May 2012.
- "Cigarettes' Role in Fires Growing". Consumeraffairs.com. Retrieved 24 May 2012.
- Joe Nickell (March–April 1998). "Fiery tales that spontaneously destruct – reports on spontaneous human combustion – includes an investigative chronology based on a published photograph". Skeptical Inquirer 22.2.
- Palmiere C, Staub C, La Harpe R, Mangin P (2009). "Ignition of a human body by a modest external source: a case report". Forensic Sci Int 188 (1–3): e17–9. doi:10.1016/j.forsciint.2009.03.027. PMID 19410396. CS1 maint: Multiple names: authors list (link)
- Campbell, S. J.; S. Nurbakhsh (1999). "Combustion of animal fat and its implications for the consumption of human bodies in fires". Science & Justice 39 (1): 27–38.
- Watson, Stephanie. "How Spontaneous Human Combustion Works". HowStuffWorks. HowStuffWorks Inc. Retrieved 24 September 2011.
- Nickell, Joe (November–December 1996). "Not-So-Spontaneous Human Combustion". Skeptical Inquirer 20.6. Retrieved 16 August 2010.
- Ford, Brian J. (2012). "Solving the Mystery of Spontaneous Human Combustion" (PDF). The Microscope (60): 63–72. Retrieved 23 August 2012.
|When were rumen microbes first discovered?|
The single-celled animals (protozoa) living in the rumen were first discovered in 1843. Later that century, other researchers discovered that a range of bacteria also lived in this part of the gut. By the end of the 19th century, scientists were coming to realise that microorganisms were important in helping ruminant animals to gain nutrients from their food (Hungate, 1966). For example, when they killed the rumen bacteria in a sample of stomach contents (using an antiseptic) and then mixed the fluid with cellulose, the cellulose wasn’t digested. But when rumen fluids and cellulose were mixed together without an antiseptic, various gases and acids were produced, which showed that the cellulose had been broken down. This was followed by research looking at what was actually produced during rumen fermentation. It turned out that one product, short-chain fatty acids, provided a large proportion of a cow’s energy needs (Annison and Bryden, 1998).
Now we know that cows need rumen microorganisms to survive. Even though cows eat grass, they can’t digest it on their own. This is because cows can’t make the enzymes needed to break down some parts of plant cells. For example, cows can’t digest cellulose. To do this, they need an enzyme called cellulase. This is why the microorganisms are so important- they produce the cellulase and other enzymes necessary to break down the parts of plant cells that the cow can’t digest. Many different types of microorganisms live in cow guts, making different enzymes to break down different parts of plants.
Protein-structure model of cellulase
The microorganisms digest the plant material and produce short-chain fatty acids, which the cow can then absorb through its gut wall and use for energy. As well as this, the cow also digests some of the microorganisms every day as they are washed out of the rumen into the abomasum. So you could say that the cow’s diet is actually made up of grass and microbes, not just the grass that it eats.
How can the microorganisms stay alive if some of them are always being digested by the cow? They keep their population numbers up by growing very quickly - they need to be able to reproduce before the food leaves the rumen. They can also attach themselves to solid lumps of food in the rumen to avoid being flushed out with rumen liquids.
Cows and their gut microbes are an example of symbiosis - two organisms living together. The relationship between cows and their gut microorganisms is mutualistic. This means that both organisms benefit from the relationship. The microbes get a suitable place to live and a supply of food delivered to their door. The cow gets energy from digesting the gut microbes and the short-chain fatty acids they produce.
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The number of microbes in one drop of rumen fluid is more than 10 times bigger than the number of people on Earth! (If there are 1012 microbes in 1ml of fluid, then 1 drop (1/20ml) contains 50,000,000,000. And 2008 data from the US Census Bureau tell us that there are around 6,602,000,000 people on Earth.)
That’s a lot of microbes - about one thousand billion, or 1012, or 1,000,000,000,000 organisms per millilitre (Prescott, Harley & Klein, 2005). To give you an idea of how many there are in total, the rumen may hold up to 95 litres of food & fluid.
There are all sorts of different types of microbes in the rumen, such as fungi, bacteria and single-celled eukaryotic organisms called protozoans. There are also some archaea, which are ancient microorgansisms that produce methane.
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Bacteria are the most important microbes involved in ruminant digestion, and there are many different types in the rumen (Prescott, Harley & Klein, 2005). Almost all of the rumen bacteria will die if they are exposed to oxygen- they are obligately anaerobic (Hungate, 1975). Here we'll look at some of the most important bacterial groups in the rumen - their relatives include some very useful microbes as well as some that make us sick.
But first - something on how they're classified.
So, back to the bacteria.
The Lactobacillales are usually harmless to humans- not all germs will make you sick! “Lacto” means “milk,” and this gives us a clue about where these bacteria are found and what they're used for - making cheese and yoghurt. Others are used to make beer and wine.
However, there are also harmful bacteria in this group, such as Staphylococcus aureus, which can cause infections, boils, abscesses and pneumonia in humans. You may have heard of “super bugs” infecting people in hospitals- these are often strains of S. aureus which have evolved to become resistant to antibiotics.
One species from this group, Streptococcus bovis, uses a wide diet of different food sources in the rumen, such as sugars and proteins, to make short-chain fatty acids.
Class ClostridiaThis class contains some important rumen bacteria that are able to digest a wide range of plant materials. Butyrivibrio fibrisolvens, a member of this class, is able to ferment a wide range of substrates, including cellulose, xylan (a structura polysaccharide similar to cellulose), proteins, sugars and fats. Close relatives of these rumen microorganisms are also found in the human gut (Fig. 1.). Other relatives of these bacteria are responsible for the diseases tetanus and botulism.
Fig. 1. Clostridium difficile obtained from a human gut.
Source: Wiggs, 2007.
A large proportion of rumen bacteria belong to this group. These bacteria are rod-shaped and cannot survive in the presence of oxygen - they are obligate anaerobes (Fig. 2) (Prescott, Harley & Klein, 2005). An important member of this group that is found in the rumen is Bacteroides succinogenes, a cellulose fermenter (Hungate, 1966).
Fig. 2. Bacteroides biacutis. Source: Dowell, 2006.
The phylum Proteobacteria is the largest and most diverse group of bacteria. They have many different shapes and ways of living. Some are free-living, some are parasitic, and others form mutualistic relationships with other organisms, such as those found in the rumen. Many Proteobacteria are responsible for diseases in animals and humans, such as Salmonella sp., which can cause typhoid.
This order contains some bacteria found in the guts of other animals as well as ruminants. Just like cows, we need gut microorganisms to help digest our food. Escherichia coli (Fig. 3) is found in the guts of humans and animals.
Fig. 3. A scanning electron micrograph of Escherichia coli.
Source: Rocky Mountain Laboratories, NIAID, NIH, 2005.
Methane-producing bacteria (Phylum Euryarchaeota)
These organisms belong to the domain Archaea, an ancient group separate from the eukaryotes and bacteria. The Archaea in the rumen use hydrogen gas and carbon dioxide to produce methane. This regulates fermentation in the rumen by lowering the amount of hydrogen gas, allowing bacteria which produce hydrogen to carry on metabolising. Some species that produce methane in the rumen include Methanobrevibacter ruminantium, Methanobacterium formicicum and Methanomicrobium mobile.
Note: Bacterial names
Bacteria are often named for their shape. The name coccus comes from the Greek word meaning “granules” and is used to name spherical cells, such as those shown below (Fig. 4.). Rod-shaped bacteria are also very common- these are called bacilli. Spiral-shaped cells are called Spirilla, and if they are flexible, spiral-shaped bacteria are called spirochaetes. What about the bacteria Staphylococcus? Staphyle means “bunch of grapes” in Greek, and coccus means “granules”, so Staphylococcus means “bunches of granules”- which is just what they look like (Fig. 4).
Fig. 4. Scanning electron micrograph of Staphylococcus aureus. Source: Ardurino and Carr, 2007.
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Most of the protozoa found in the rumen are ciliates (phylum Ciliophora). Many ciliates use cilia (tail-like structures) to move around, and to move food particles into their mouths. Most ciliates do not live inside another organism, but some exist in the rumen, such as Entodinium. In the rumen, two types of ciliates are found; the holotrichs and the spirotrichs. The holotrichs convert soluble sugars into starch, while spirotrichs consume starch and cellulose (Hungate, 1975).
The fungi in the rumen are a bit different to the mushrooms in your local supermarket. They are very small (Fig. 5) - note that the scale bar on this diagram is 50µm, or 50 millionths of a metre. Unlike mushrooms, rumen fungi don’t need oxygen to survive: they are anaerobes. Rumen fungi have been shown to digest cellulose and xylans, which shows that they may play a role in helping the ruminant host to digest plant matter.
Fungi are very important to humans. They are excellent recyclers, breaking down animal and plant matter into molecules that can be re-used by other organisms. Yeasts, a type of fungi, are used to make bread, wine and beer. Fungi also cause many diseases in plants and animals, such as the human diseases athlete’s foot and ringworm.
Fig. 5. Candida albicans, the fungus that causes thrush in humans, magnified 200 times. Source: Y tambe, 2005
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To obtain energy for growth and reproduction, organisms must break down large molecules into smaller ones. This process gives energy and is called catabolism. For growth to occur, larger molecules are made from smaller ones, using up energy. This process is called anabolism. Both processes are part of cellular metabolism.
When plant material, such as grass, enters a cow's stomach, microorganisms immediately get to work to break it down. They do this with enzymes. Ruminants are unable to synthesise the enzymes needed to digest cellulose and other plant compounds. The microbes in the rumen, however, are able to make the various enzymes needed to hydrolyse cellulose, proteins, sugars and other materials.
Rumen bacteria need carbon dioxide, nitrogen, sodium, and volatile fatty acids to grow (Hungate, Bryant & Mah, 1964). Some bacteria use only one type of food, but others use a range of different types (Table 1). Many bacteria are able to digest cellulose. Many can also digest xylan, a type of complex carbohydrate similar to cellulose. Others can digest proteins, or sugars such as amylose and lactose.
Glucose is released when cellulose is digested. Various microbes then ferment the glucose to produce short-chain fatty acids (SCFAs). The SCFAs are then taken up and used by the host animal. Carbon dioxide and methane gas are also produced by the microbes and are excreted by the host (e.g. in exhaled air & by belching).
Table 1. Sources of carbon, energy and electrons and their definitions. (Modified from Prescott, Harley & Klein, 2005)
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Because there is very little oxygen present in the rumen, the microorganisms there must obtain energy from their food anaerobically (without oxygen). This is done through a process called fermentation. Fermentation involves the breakdown of glucose into alcohols or acids. Sound familiar? Fermentation is also used to make alcoholic drinks such as beer and wine. As we’ll see, it doesn’t yield as much energy as aerobic respiration.
Before fermentation can occur, larger molecules present in the plant material, such as lipids, proteins and polysaccharides, must first be broken down into their component parts. This is done by hydrolysis. Through hydrolysis, lipids are broken down into glycerol and fatty acids; proteins into amino acids, and polysaccharides into glucose and other simple sugars. Here, we’ll look at fermentation using glucose.
Whether there is oxygen present or not, the first step of respiration is glycolysis. In this process, glucose is broken down to form a compound called pyruvate. Glycolysis also generates 2 ATP molecules (the cell’s energy carriers) and 2 of NADH.
In anaerobic environments like the rumen, glycolysis may be followed by homolactic fermentation. This is a ‘recycling’ step that doesn’t generate any more ATP. Homolactic fermentation converts pyruvate into lactate and converts the NADH produced in glycolysis back into NAD+ so that it can be used again.
In our own cells (like those of all eukaryotes), where oxygen is present, further energy can be produced from pyruvate using the Krebs cycle and oxidative phosphorylation, producing a net total of 36 ATP per glucose molecule. However, this is ruled out in the anaerobic environment of the rumen.
The sparknotes site has a diagram showing how fermentation works.
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An online textbook written by an American university professor containing good general information about microbiology, also with some information on how microbes can affect human health
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