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 (176–194°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): 879–84.

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

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 176–199°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.

Spore

A spore is an extremely tiny, specialized package of cells used by some organisms during reproduction. Plants use spores as they do seeds, for reproduction; while certain algae, fungi, bacteria, and protozoans use spores to help disperse themselves widely and to protect themselves from unfavorable conditions. Spores vary in size but all are microscopic and usually contain a single cell.

In botany (the study of plants), spores are regarded as reproductive cells that are capable of developing into a new individual plant, either directly or after fusion with another spore. Plants that do not flower, like mosses and ferns, do not grow from a seed that was created sexually by male pollen combining with a female ovule. Instead, they reproduce by means of spores. The plant that develops from a spore does not resemble the parent plant, since this plant is in the first phase of a life cycle called the "alternation of generations." This means that in the life cycle of a plant, two generations exist alternately, one after the other. For example, for centuries no one knew how ferns actually reproduced. Most thought that since a fern was a green plant, it had to produce seeds (and therefore reproduce sexually with male and female sex cells). Yet it was impossible to find a fern's seeds until botanists studied the entire life cycle of a fern. Finally, they discovered that ferns reproduce with spores. They also discovered that a fern has a sexual stage (producing sperm and egg) that alternates with an asexual stage (producing spores). In the life cycle of a fern, a mature fern plant develops little brown spore cases called sporangia that are attached to the underside of their leaves, or fronds. When the spores are ripe, the cases split open in the dry air and the dustlike spores are carried away by the wind. When the spore lands where there are damp conditions, it germinates (begins to sprout) and grows into a very small, heart-shaped plant. This tiny plant begins to mature and develops sex organs which, after fertilization (the process in which an egg cell and a sperm cell unite to form one cell) occurs, grows into a plant we recognize as a fern.

Organisms besides plants use spores for other purposes. Certain kinds of algae, bacteria, fungi, and protozoans all form what are described as survival spores. Besides the ability of spores to be easily and widely dispersed, they also have the ability to survive under harsh conditions. For fungi that are not able to move, spores are an ideal way to spread themselves around, and when conditions are right, fungi produce dispersal spores that function like seeds and germinate quickly under proper conditions. They grow, mature, and produce more spores out of which more fungi will grow. But when the environment becomes unfavorable—too hot or cold or too dry—fungi produce survival spores that may live for years before germinating. Certain types of bacteria form spores for protective reasons. Bacterial spores, which are bacterial cells that have gone dormant (resting) and developed a thick, hard wall, can usually survive even in hot, boiling water. Protozoans—most of which are parasites that live in or on other animals—also form protective spores by a type of cell division. The protozoan that causes malaria is injected into a healthy person by a mosquito carrying its spores. Although the spores cannot move, they multiply by cell division in the person's liver and then enter the blood cells. Soon the blood cells burst and release the spores into the liquid part of the blood. When a mosquito stings this infected person and takes its blood, it also takes the spores and eventually deposits them into yet another healthy person. For plants and other organisms, spores have proven to be a successful means of establishing themselves in new environments as well as a way of surviving unfavorable conditions.

[See alsoAlgae; Botany; Bacteria; Fungi; Plant Reproduction; Plants; Protozoans ]

Spore

In zoology, spores are structures that are used by organisms to survive a period of unfavorable environmental conditions, and can subsequently regenerate into the adult form once the environment again becomes favorable for growth. Depending on the species , spores are asexual, resting bodies, which can be one-celled or multi-cellular.

Many protozoans have a stage in their life cycle that involves the development of a spore or cyst that is capable of surviving a period of environmental conditions that are unfavorable for growth. This is especially common among parasitic protozoans, which must survive the unfavorable conditions that are encountered during transmission from host to host, often through the ambient environment. Other, free-living protozoans commonly develop a spore stage to survive periods of severe environmental stress , for example, when a pond dries up during late summer or freezes during winter.

Many types of bacteria , fungi , actinomycetes, yeasts, and algae also develop spores as resting stages to survive periods of unfavorable environmental conditions. A commonly known spore-forming bacterium is Bacillus anthracis, the bacterium that causes anthrax . Anthrax spores can survive in soil for several years, and pose a threat mainly to animals and livestock .

In addition, most fungi develop spores as part of their generative process. Fungi produce diploid spores in specialized organs known as sporangia. Fungal spores are capable of developing into a mature organism once favorable environmental conditions are encountered. Fungal spores are extremely light and can be carried for great distances by wind or water , and they are therefore an extremely effective means of long-distance dispersal. Liverworts and mosses also produce small diploid spores as a means of achieving an extensive dispersal of their asexual progeny to colonize new habitats.

In botany , spores are reproductive cells that are capable of developing into a new individual plant , either directly or after fusion with another spore. Plant spores known as gonidia are developed by mitosis , or the process of division and separation of chromosomes that occurs in a dividing cell . Mitosis produces two diploid daughter cells, each with the same chromosomal content as their parent cell. These types of spores are capable of producing a mature organism without undergoing fusion with another type of spore. The diploid spores of club-mosses and ferns , which are vascular plants, are bisexual structures that are used to propagate and disperse the plants.

Plant spores known as meiospores are developed through the process of meiosis . Meiosis refers to reduction division of a diploid cell, which results in the formation of two haploid spores, each of which contains one of the two sets of chromosomes of the parent cell. Vascular plants produce two types of haploid spores. Megaspores are usually larger and are regarded as the female spore in sexual reproduction of plants, because the female gametophyte develops from these types of spores. Microspores are smaller, and they develop into the male gametophyte. Fusion of the male and female gametophytes leads to the development of plant seeds , which are diploid structures that culminate sexual reproduction in higher plants. Seeds can be dispersed into the environment to colonize new habitats and perpetuate the species.

Researching spore development and survival has aided medical science for over a century. In the 1940s, one of the initial obstacles to the mass-manufacture of the antibiotic Penicillin was the environmental sensitivity of its reproductive spores. The development of new methods to culture penicillin in large quantities lead not only to the wide availability of natural penicillin, but also to the creation of synthetic, or lab created, alternative antibiotics . Pollen and mold allergies, including the manner in which some airborne spores produce certain reactions in humans, have been a focus of spore-related research since 1880. Today, they remain a key interest of research and development in the pharmaceutical industry.

See also Asexual reproduction; Protozoa.

Bill Freedman

Spore

Spores are structures that are used by organisms to survive a period of unfavorable environmental conditions. Regeneration of the organism into the adult form occurs once the environment again becomes favorable for growth. This period of dormancy can last for a century or more in the case of some spore-forming microorganisms.

Depending on the species, spores are asexual, resting bodies, which can be one-celled or multi-cellular.

Many protozoans have a stage in their life cycle that involves the development of a spore or cyst that is capable of surviving a period of environmental conditions that are unfavorable for growth. This is especially common among parasitic protozoans, which must survive the unfavorable conditions that are encountered during transmission from host to host, often through the ambient environment. Other, free-living protozoans commonly develop a spore stage to survive periods of severe environmental stress, for example, when a pond dries up during late summer or freezes during winter.

Many types of bacteria, fungi, actinomycetes, yeasts, and algae also develop spores as resting stages to survive periods of unfavorable environmental conditions. A commonly known spore-forming bacterium is Bacillus anthracis, the bacterium that causes anthrax. Another bacterium, Clostridium botulinum can survive in canned foods in spore form. The resuscitated form can be lethal if ingested. Anthrax spores can survive in soil for several years, and pose a threat mainly to animals and livestock. However, as the anthrax incidents in the United States in the autumn of 2001 point out, the deliberate use of anthrax spores as a bioterrorist weapon is possible.

Most fungi develop spores as part of their generative process. Fungi produce diploid spores in specialized organs known as sporangia. Fungal spores are capable of developing into a mature organism once favorable environmental conditions are encountered. Fungal spores are extremely light and can be carried for great distances by wind or water, and they are therefore an extremely effective means of long-distance dispersal. Liverworts and mosses also produce small diploid spores as a means of achieving an extensive dispersal of their asexual progeny to colonize new habitats.

In botany, spores are reproductive cells that are capable of developing into a new individual plant, either directly or after fusion with another spore. Plant spores known as gonidia are developed by mitosis, or the process of division and separation of chromosomes that occurs in

a dividing cell. Mitosis produces two diploid daughter cells, each with the same chromosomal content as their parent cell. These types of spores are capable of producing a mature organism without undergoing fusion with another type of spore. The diploid spores of club-mosses and ferns, which are vascular plants, are bisexual structures that are used to propagate and disperse the plants.

Plant spores known as meiospores are developed through the process of meiosis. Meiosis refers to reduction division of a diploid cell, which results in the formation of two haploid spores, each of which contains one of the two sets of chromosomes of the parent cell. Vascular plants produce two types of haploid spores. Megaspores are usually larger and are regarded as the female spore in sexual reproduction of plants, because the female gametophyte develops from these types of spores. Microspores are smaller, and they develop into the male gametophyte. Fusion of the male and female gametophytes leads to the development of plant seeds, which are diploid structures that culminate sexual reproduction in higher plants. Seeds can be dispersed into the environment to colonize new habitats and perpetuate the species.

Bill Freedman