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Spores

Spores

BRIAN HOYLE

A spore is a hard casing that contains the genetic material of those bacteria and other microorganisms that are able to form the structure. This physically and chemically resilient package protects the genetic material during periods

when the environmental conditions are so harsh that the growing form of the microbe would be killed.

The effect of temperature on bacterial and spore survival provides a good example of the resilience of bacterial spores. Temperatures of 80 to 90° Celsius (176194°F) typically kill bacteria that are growing and dividing within minutes. These high temperatures cause structural components of the bacteria to dissolve, and strands of genetic material to separate from one another. A group of bacteria known as thermophilic bacteria can survive these temperatures, but temperatures of 120°C (248°F) kill even thermophiles. In contrast, spores can survive exposure to 120°C for several hours.

Spores of bacteria that subsequently could be revived into the growing form have been recovered from materials that are over a century old. Thus, spores offer an extraordinary form of protection to bacteria. Anthrax spores that could germinate into living bacteria were recovered on Gruinard Island, an island off the coast of Scotland that was used for biological weapons testing by the British government during World War II.

Spores are noteworthy in terms of security because of the threat they pose in the hands of terrorists. Bacillus anthracis, the bacterium that causes anthrax, is a spore former. The spores are very light and tiny. As a result, they can be readily dispersed through the air and can be easily inhaled into the lungs. The resulting lung infection, which is called inhalation anthrax, is almost always fatal without prompt medical treatment. Anthrax spores were used as a mechanism of bioterrorism to target United States citizens by deliberate dispersal in the mail system in late 2001.

Another prominent example of a bacterial spore former of concern is Clostridium botulinum. The bacterium and the spore are widespread in nature; for example, they are a common inhabitant of the soil. This bacterium can also survive in canned foods for extended time periods, even when the food has been heated or is acidic. When the food is eaten, the dormant bacteria begin to grow again and produce a variety of potent toxins that disrupt the nervous system, causing serious illness.

The contamination of foods by terrorists is a significant security concern, especially in the United States. Because the spores are hardy and can be transported virtually undetected, they could be taken to food plants or supermarkets, where the food could be contaminated. The spores would survive to cause illness.

Other microorganisms of human concern that form spores include protozoa (e.g., Microsporidia ) and fungi (e.g., Actinomycetes).

Formation of bacterial spores. The multistep process of forming a spore is known as sporulation. The process begins when a bacterium senses that the environmental conditions are becoming life threatening. Bacteria are equipped with a whole battery of sensing proteins and other compounds that monitor environmental conditions of temperature, pH of the surrounding fluid, water content, and availability of food, as some examples. After monitoring the environment for a period of time, the deteriorating conditions trigger the microbe to begin the change from a growing and dividing cell to a dormant spore.

The genetic material of the bacterium is duplicated. Then, the membrane coat that surrounds the inside of the bacterium pinches inward until the ends of the inward growing membrane meet. This isolates one of the copies of the genetic material from the remainder of the bacterium. This smaller cell is called a daughter cell. The remainder of the bacterium is called the mother cell.

In the next stage of spore formation, the membrane that surrounds the mother cell surrounds the daughter cell. This creates a daughter cell that is surrounded by two layers of membrane. Between these two membranes a think layer of a rigid material forms. This layer is called peptidoglycan. Peptidoglycan is normally present in the bacterial cell wall, but not in nearly the same amount. The thick peptidoglycan makes the double membrane layer very tough and hard to break apart. Finally, this tough membrane is coated on the outer surface by proteins. The proteins are also resistant to breakage.

The remnants of the mother cell dissolve away leaving the spore. The spore is essentially in hibernation. There is very little chemical activity. Nevertheless, the spore is able to monitor the external environment and, when conditions are sensed as being more favorable, the conversion from the spore form to the growing organism begins.

The threat from spores. The threat from spores, particularly anthrax spores, lies in their small size and powdery texture once they have been dried. As shown in the anthrax attacks in the United States in 2001, anthrax spores can be delivered to someone in a letter. The spores escape detection using methods like an x-ray. When the letter is opened, the spores can be dispersed in the air and breathed in.

Studies in animal models have shown that even the inhalation of a few spores is enough to cause an infection. The lung is an ideal environment for the anthrax bacterium. Food is available and the atmosphere is warm and moist. When the spores germinate into growing bacteria, the resulting infection can feel similar to the flu at first. Thus, a victim may not seek treatment, believing that the illness will pass in a few days. By the time the true nature of the infection is discovered, the infection can be so advanced as to be fatal.

Anthrax spores could also potentially be dispersed from an airplane or a balloon. Indeed, the terrorists responsible for the September 11, 2001 attacks on the World Trade Center and the Pentagon had explored the use of crop dusting aircraft. Models developed by the U.S. government have predicted that a few hundred pounds of anthrax spores released upwind of Washington, D.C. could cause at least several hundred thousand deaths within a few days.

The growing of the amounts of bacteria necessary to prepare large amounts of powdered spores and the preparation of the spores is not an easy task. Nonetheless, many microbiologists are capable of the task, and the construction of a facility that is large enough to house the needed equipment is not overly difficult. In the past century, nations including the U.S. and Russia had active anthrax weaponization programs. Prior to Operation Iraqi Freedom, Iraq was suspected of having an anthrax weapons development program.

Protection from spores. The threat posed by the use of spores in the mail is difficult to counter. Researchers are working to develop sensors that detect the spores, based on the reaction of antibodies with target proteins on the surface of the spores. However, such detection requires physical contact with the spores. Methods that do not require the opening of letters, such as irradiation, are being tested and refined in the field and in the laboratory.

Another tact is the use of compounds that can destroy the spore. For example, in 2002, researchers discovered that an enzyme called PlyG lysin will chemically crack apart the spore coat. The spore contents are released and disintegrate. Until such sophisticated detection and protection methods are perfected, the treatment of a site contaminated with spores will continue to include the use of bleach.

FURTHER READING:

BOOKS:

Fischetti, Vincent, Richard P. Novick, Joseph J. Ferretti, and Danile A. Portnoy. Gram-Positive Pathogens. Washington: American Society for Microbiology Press, 2000.

Storz, Gisela, and Regine Hengge-Aronis. Bacterial Stress Responses. Washington: American Society for Microbiology Press, 2000.

Caipo, M.L., S. Duffy, L. Zhao, et al."Bacillus megaterium Spore Germination is Influenced by Inoculum Size." Journal of Applied Microbiology. no. 92 (2002): 87984.

ELECTRONIC:

American Society for Microbiology. "Microbial Spore Formation." Microbe.org. 1999. <http://www.microbe.org/microbes/spores.asp>(10 January 2003).

SEE ALSO

Anthrax, Terrorist Use as a Biological Weapon
Anthrax Weaponization
Biological Warfare
Food Supply, Counter-Terrorism
Mail Sanitization
Pathogens
Weapons of Mass Destruction, Detection

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Spores

Spores

Illness and death can occur from pathogenic (disease-causing) microbial infections. Thus knowledge of the ways infections spread and the myriad of symptoms that can develop are a vital part of forensic science . This is especially important when the infection is a serious threat to health and is easily spread from person to person. One important contributor to the spread of infection by certain bacteria (including the infamous cause of anthrax ) is the spore.

A spore is a hard casing that contains the genetic material of those bacteria and other microorganisms that are able to form the structure. This physically and chemically resilient package protects the genetic material during periods when the environmental conditions are so harsh that the growing form of the microbe would be killed.

The effect of temperature on bacterial and spore survival provides a good example of the resilience of bacterial spores. Temperatures of 176199°F (80 90°C) typically kill bacteria that are growing and dividing within minutes. These high temperatures cause structural components of the bacteria to dissolve, and strands of genetic material to separate from one another. A group of bacteria known as thermophilic bacteria can survive these temperatures; but, temperatures of (248°F) 120°C kill even thermophiles. In contrast, spores can survive exposure to 248°F for several hours.

Spores of bacteria that subsequently could be revived into the growing form have been recovered from materials that are over a century old. Thus, spores offer an extraordinary form of protection to bacteria. Anthrax spores that could germinate into living bacteria were recovered on Gruinard Island, an island off the coast of Scotland, that was used for biological weapons testing by the British government during World War II.

Bacillus anthracis, the bacterium that causes anthrax, is a spore former. The spores are very light and tiny. As a result, they can be readily dispersed through the air and can be easily inhaled into the lungs. The resulting lung infection, which is called inhalation anthrax, is almost always fatal without prompt medical treatment.

Another prominent example of a bacterial spore former of concern is Clostridium botulinum. The bacterium and the spore are widespread in nature. For example, they are a common inhabitant of the soil. This bacterium can also survive in canned foods for extended time periods, even when the food has been heated or is acidic. When the food is eaten, the dormant bacteria begin to grow again and produce a variety of potent toxins that disrupt the nervous system, causing serious illness.

Other microorganisms of human concern that form spores include protozoa (e.g., Microsporidia ) and fungi (e.g., Actinomycetes ).

The multi-step process of forming a spore is known as sporulation. The process begins when a bacterium senses that the environmental conditions are becoming life threatening. Bacteria are equipped with a whole battery of sensing proteins and other compounds that monitor environmental conditions, such as temperature, pH of the surrounding fluid, water content, and availability of food. After monitoring the environment for a period of time, the deteriorating conditions trigger the microbe to begin the change from a growing and dividing cell to a dormant spore.

The genetic material of the bacterium is duplicated. Then, the membrane coat that surrounds the inside of the bacterium pinches inward until the ends of the inward growing membrane meet. This isolates one of the copies of the genetic material from the remainder of the bacterium. This smaller cell is called a daughter cell. The remainder of the bacterium is called the mother cell.

In the next stage of spore formation, the membrane that surrounds the mother cell surrounds the daughter cell. This creates a daughter cell that is surrounded by two layers of membrane. Between these two membranes a thick layer of a rigid material forms. This layer is called peptidoglycan. Peptidoglycan is normally present in the bacterial cell wall, but not in nearly the same amount as is present in a spore. The thick peptidoglycan makes the double membrane layer very tough and hard to break apart. Finally, this tough membrane is coated on the outer surface by proteins. The proteins are also resistant to breakage.

The remnants of the mother cell dissolve away leaving the spore. The spore is essentially in hibernation. There is very little chemical activity. Nevertheless, the spore is able to monitor the external environment and, when conditions are sensed as being more favorable, the conversion from the spore form to the growing organism begins.

see also Anthrax; Bacterial biology; Pathogens.

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spore

spore, term applied both to a resistant or resting stage occurring among various unicellular organisms (especially bacteria) and to an asexual reproductive cell produced by many unicellular plants and animals and by all plants that undergo an alternation of generations. A spore is typically a cell surrounded by a cell wall; in resistant spores and in the resting stage of reproductive spores this wall becomes tough and waterproof, permitting the cell to survive unfavorable circumstances such as extremes of temperature and moisture. Upon germination, spores that were generated asexually may produce cells or multicellular forms that can engage in sexual reproduction. Many unicellular plants and animals reproduce both by the formation of spores and by simple cell division (mitosis). Yeasts, for instance, reproduce by forming spores as well as by budding. Among the fungi some spores are thin-walled and germinate quickly; others are thick-walled resistant types. In multicellular plants the sporophyte generation produces (by meiosis) spores with half the normal number of chromosomes for the species; these grow directly into the gametophyte generation, which produces (by mitosis) male and female reproductive cells that when united give rise to a sporophyte.

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spore

spore A propagative plant body consisting of a gametophyte enclosed in a non-cellular coat. Spores are enclosed within a capsule (sporangium) and are produced in groups of four (tetrads) when the parent cell divides meiotically. In more primitive plants the spores are identical (isospore) and the condition is called ‘homospory’. In more advanced, vascular plants spores of two sizes are produced and the condition is called ‘heterospory’. Small, male microspores are contained within a microsporangium; larger, female megaspores within megasporangia. Where spores occur in tetrads the contact surfaces produce a ‘trilete’ mark on each of the four spores, marking the point for the germination of the prothallus. Less commonly, two contact surfaces are produced, resulting in a ‘monolete’ marking. Spores which were probably produced singly are ‘alete’, with no obvious marking.

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spore

spore A reproductive cell that can develop into an individual without first fusing with another reproductive cell (compare gamete). Spores are produced by plants, fungi, bacteria, and some protoctists. A spore may develop into an organism resembling the parent or into another stage in the life cycle, either immediately or after a period of dormancy. In plants showing alternation of generations, spores are formed by the sporophyte generation and give rise to the gametophyte generation. In ferns, the rows of brown reproductive structures on the undersurface of the fronds are spore-producing bodies.

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spore

spore / spôr/ • n. Biol. a minute, typically one-celled, reproductive unit capable of giving rise to a new individual without sexual fusion, characteristic of lower plants, fungi, and protozoans. ∎  Bot. (in a plant exhibiting alternation of generations) a haploid reproductive cell that gives rise to a gametophyte. ∎  Microbiology (in bacteria) a rounded resistant form adopted by a bacterial cell in adverse conditions.

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spore

spore
1. (mycol.) A microscopic structure which functions in reproduction and dispersal. A spore does not contain an embryo and thus is distinct from a seed. Many different types of spore are produced by fungi
.
2. (bacteriol.) A differentiated cell which may function as a propagule or as a resistant structure that allows the organism to survive adverse environmental conditions. See also HETEROSPORY; HOMOSPORY; MEGASPORE; MICROSPORE; and POLLEN.

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spore

spore Small, reproductive body that detaches from the parent organism to produce new offspring. Mostly microscopic, spores may consist of one or several cells (but do not contain an embryo) and are produced in large numbers. Some germinate rapidly, others ‘rest’, surviving unfavourable environmental conditions. Spores are formed by ferns, horsetails, mosses, fungi and bacteria.

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spore

spore
1. A microscopic structure which functions in the reproduction and dispersal of fungi. A spore does not contain an embryo and is thus distinct from a seed. Many different types of spore are produced by fungi.

2. A differentiated bacterial cell which may function as a propagule or as a resistant structure that allows the organism to survive adverse environmental conditions.

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spore

spore (spor) n. a small reproductive body produced by plants and microorganisms. Some kinds of spores function as dormant stages of the life cycle, enabling the organism to survive adverse conditions. Other spores are the means by which the organism can spread vegetatively. See also endospore.

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spores

spores The resting state of some bacteria; thick‐walled and highly resistant to heat. Under suitable conditions they germinate to produce bacteria. Spore‐forming bacteria are a health hazard because they can survive pasteurization and sterilization.

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spore

sporeabhor, adore, afore, anymore, ashore, awe, bandore, Bangalore, before, boar, Boer, bore, caw, chore, claw, cocksure, comprador, cor, core, corps, craw, Delors, deplore, door, draw, drawer, evermore, explore, flaw, floor, for, forbore, fore, foresaw, forevermore, forswore, four, fourscore, furthermore, Gábor, galore, gnaw, gore, grantor, guarantor, guffaw, hard-core, Haugh, haw, hoar, ignore, implore, Indore, interwar, jaw, Johor, Lahore, law, lessor, lor, lore, macaw, man-o'-war, maw, mirador, mor, more, mortgagor, Mysore, nevermore, nor, oar, obligor, offshore, onshore, or, ore, outdoor, outwore, paw, poor, pore, pour, rapport, raw, roar, saw, scaur, score, senhor, señor, shaw, ship-to-shore, shop-floor, shore, signor, Singapore, snore, soar, softcore, sore, spore, squaw, store, straw, swore, Tagore, tau, taw, thaw, Thor, threescore, tor, tore, torr, trapdoor, tug-of-war, two-by-four, underfloor, underscore, war, warrantor, Waugh, whore, withdraw, wore, yaw, yore, your

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