An endospore is a dormant Dormancy is a period in an organism's life cycle when growth, development, and physical activity is temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions. Organisms can synchronize entry to a dormant phase with their, tough, and non-reproductive structure produced by certain bacteria from the Firmicute The Firmicutes are a phylum of bacteria, most of which have Gram-positive cell wall structure. A few however, such as Megasphaera, Pectinatus, Selenomonas, and Zymophilus, have a porous pseudo-outer-membrane that causes them to stain Gram-negative. Scientists once classified the Firmicutes to include all Gram-positive bacteria, but have recently phylum. The name "endospore" is suggestive of a spore or seedlike form (endo means within), but it's not a true spore In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoans. A chief difference between spores and seeds as dispersal units is that spores have very little stored (not an offspring). It's a kind of stripped-down, dormancy form that the bacterium can reduce itself to. The endospore becomes important when the bacterium is experiencing an environment that is deleterious to the usual vegetative state of the bacterium, notably including when the bacterium is getting dried out (desiccated). Endospores enable the survival of a bacterium through periods of environmental stress. When the environment returns to favorable, the endospore can reactivate itself to the vegetative state. Not all, nor even most, types of bacteria can change to the endospore form. Examples that can include Bacillus Bacillus is a genus of Gram-positive rod-shaped bacteria and a member of the division Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes, and test positive for the enzyme catalase. Ubiquitous in nature, Bacillus includes both free-living and pathogenic species. Under stressful environmental conditions, the cells produce and Clostridium Clostridium is a genus of Gram-positive bacteria, belonging to the Firmicutes. They are obligate anaerobes capable of producing endospores. Individual cells are rod-shaped, which gives them their name, from the Greek kloster or spindle. These characteristics traditionally defined the genus, however many species originally classified as Clostridium.^[1]

The endospore consists of the bacterium's DNA and part of its cytoplasm, surrounded by a very tough outer coating.

Endospores can survive without nutrients. They are resistant to ultraviolet radiation, desiccation, high temperature, and chemical disinfectants. Common anti-bacterial agents that work by destroying vegetative cell walls don't work on endospores. Endospores are commonly found in soil and water, where they may survive for long periods of time.

Some classes of bacteria can turn into exospores, a.k.a. microbial cysts A microbial cyst is a resting or dormant stage of a microorganism, usually a bacterium or a protist, that helps the organism to tide over unfavorable environmental conditions. It can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed down and the cell ceases all activities like feeding and, instead of endospores. Exospores and endospores are two kinds of "hibernating" or dormant stages seen in some classes of microorganisms.

Structure

In contrast to eukaryotic spores In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoans. A chief difference between spores and seeds as dispersal units is that spores have very little stored, which are produced by many eukaryotes A eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the for reproductive purposes, bacteria will produce a single endospore internally. The spore is sometimes surrounded by a thin covering known as the exosporium, which overlies the spore coat. The spore coat, which acts like a sieve A sieve, or sifter, separates wanted elements from unwanted material using a filter such as a mesh or net. However, in cooking, especially with flour, a sifter is used to aerate the substance, among other things. A strainer is a type of sieve typically used to separate a solid from a liquid. The word "sift" derives from sieve that excludes large toxic molecules like lysozyme Lysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase, are glycoside hydrolases, enzymes that damage bacterial cell walls by catalyzing hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. Lysozyme is, is resistant to many toxic molecules A molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense. In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules and may also contain enzymes Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their that are involved in germination Germination is the process in which a plant or fungus emerges from a seed or spore and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the growth of hyphae from fungal spores, is also germination. In a more. The cortex lies beneath the spore coat and consists of peptidoglycan Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria , forming the cell wall. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N-acetylmuramic acid. Attached to the N-acetylmuramic acid is a peptide. The core wall lies beneath the cortex and surrounds the protoplast Protoplast, from the ancient Greek πρῶτον + verb πλάθω or πλάττω (to mould: deriv. plastic), initially referred to the first organized body of a species. This meaning is similar to the non-biological definition, the first from which all subsequent forms are derived or core of the endospore. The core contains the spore chromosomal DNA Deoxyribonucleic acid ( /diːˌɒksɨˌraɪbɵ.nuːˈkleɪ.ɪk ˈæsɪd/ (help·info)) (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of is encased in chromatin Chromatin is the combination of DNA and proteins that makes up chromosomes. It is found inside the nuclei of eukaryotic cells. It is divided between heterochromatin and euchromatin (extended) forms. The major components of chromatin are DNA and histone proteins, although other proteins have prominent roles too. The functions of chromatin are to-like proteins known as SASPs, that protect the spore DNA from UV radiation and heat. The core also contains normal cell structures, such as ribosomes Ribosomes are the components of cells that make proteins from amino acids. One of the central tenets of biology, often referred to as the "central dogma," is that DNA is used to make RNA, which, in turn, is used to make protein. The DNA sequence in genes is copied into a messenger RNA . Ribosomes then read the information in this RNA and and other enzymes Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their, but is not metabolically active.

Up to 15% of the dry weight of the endospore consists of calcium dipicolinate within the core, which is thought to stabilize the DNA Deoxyribonucleic acid ( /diːˌɒksɨˌraɪbɵ.nuːˈkleɪ.ɪk ˈæsɪd/ (help·info)) (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of. Dipicolinic acid Dipicolinic acid is a chemical compound which composes 5% to 15% of the dry weight of bacterial spores. It is implicated as responsible for the heat resistance of the endospore could be responsible for the heat resistance of the spore, and calcium Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust. Calcium is also the fifth most abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, may aid in resistance to heat and oxidizing agents. However, mutants resistant to heat but lacking dipicolinic acid have been isolated, suggesting other mechanisms contributing to heat resistance are at work^[2].

Visualising endospores under the light microscope can be difficult due to the impermeability of the endospore wall to dyes and stains. While the rest of a bacterial cell may stain, the endospore is left colourless. To combat this, a special stain technique called a Moeller stain is used. That allows the endospore to show up as red, while the rest of the cell stains blue. Another staining technique for endospores is the Schaeffer-Fulton stain The Schaeffer-Fulton stain is a technique designed to isolate endospores by staining any present endospores green, and any other bacterial bodies red. The green stain is malachite green, and the counterstain is safranin, which dyes any other bacterial bodies red, which stains endospores green and bacterial bodies red. The arrangement of spore layers is as follows:

• Exosporium
• Spore coat
• Spore cortex
• Core wall

Location

The position of the endospore differs among bacterial species and is useful in identification. The main types within the cell are terminal, subterminal, and centrally placed endospores. Terminal endospores are seen at the poles of cells, whereas central endospores are more or less in the middle. Subterminal endospores are those between these two extremes, usually seen far enough towards the poles but close enough to the center so as not to be considered either terminal or central. Lateral endospores are seen occasionally.

Examples of bacteria having terminal endospores include Clostridium tetani Clostridium tetani is a rod-shaped, anaerobic bacterium of the genus Clostridium. Like other Clostridium species, it is Gram-positive, and its appearance on a gram stain resembles tennis rackets or drumsticks. C. tetani is found as spores in soil or as parasites in the gastrointestinal tract of animals. C. tetani produces a potent biological toxin,, the pathogen that causes the disease tetanus Tetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibres. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, obligate anaerobic bacterium Clostridium tetani. Infection generally occurs through wound contamination and often involves a cut or deep puncture wound. As. Bacteria having a centrally placed endospore include Bacillus cereus Bacillus cereus is an endemic, soil-dwelling, Gram-positive, rod-shaped, beta hemolytic bacterium. Some strains are harmful to humans and cause foodborne illness, while other strains can be beneficial as probiotics for animals. B. cereus bacteria are facultative anaerobes, and like other members of the genus Bacillus can produce protective, and those having a subterminal endospore include Bacillus subtilis Bacillus subtilis, known as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate extreme environmental conditions. Unlike several other well-. Sometimes the endospore can be so large the cell can be distended around the endospore, this is typical of Clostridium tetani Clostridium tetani is a rod-shaped, anaerobic bacterium of the genus Clostridium. Like other Clostridium species, it is Gram-positive, and its appearance on a gram stain resembles tennis rackets or drumsticks. C. tetani is found as spores in soil or as parasites in the gastrointestinal tract of animals. C. tetani produces a potent biological toxin,.

Formation and destruction

When a bacterium detects environmental conditions are becoming unfavourable it may start the process of endosporulation, which takes about eight hours. The DNA Deoxyribonucleic acid ( /diːˌɒksɨˌraɪbɵ.nuːˈkleɪ.ɪk ˈæsɪd/ (help·info)) (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of is replicated and a membrane wall known as a spore septum In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones begins to form between it and the rest of the cell. The plasma membrane The cell membrane is one biological membrane separating the interior of a cell from the outside environment of the cell surrounds this wall and pinches off to leave a double membrane around the DNA, and the developing structure is now known as a forespore. Calcium dipicolinate is incorporated into the forespore during this time. Next the peptidoglycan cortex forms between the two layers and the bacterium adds a spore coat to the outside of the forespore. Sporulation is now complete, and the mature endospore will be released when the surrounding vegetative cell is degraded.

Endospores are resistant to most agents that would normally kill the vegetative cells they formed from. Household cleaning products generally have no effect, nor do most alcohols In chemistry, an alcohol is any organic compound in which a hydroxyl functional group (-O , quaternary ammonium compounds Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR4+, R being an alkyl group. Unlike the ammonium ion and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged, independent of the pH of their solution. Quaternary ammonium salts or or detergents A detergent is a material used for cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning. Alkylating Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in organic molecules. Many biological target molecules agents however, such as ethylene oxide Ethylene oxide, also called oxirane, is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. Because of its special molecular structure, ethylene oxide easily participates in the addition reaction, opening its, are effective against endospores.

While resistant to extreme heat and radiation, endospores can be destroyed by burning or by autoclaving An autoclave is a device to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 °C or more, typically for 15 to 20 minutes depending on the size of the load and the contents. It was invented by Charles Chamberland in 1879, although a precursor known as the steam digester was created by Denis Papin in 1679. Endospores are able to survive boiling at 100°C for hours, although the longer the number of hours the fewer that will survive. An indirect way to destroy them is to place them in an environment that reactivates them to their vegetative state. They will germinate within a day or two with the right environmental conditions, and then the vegetative cells can be straightforwardly destroyed. This indirect method is called Tyndallization. It was the usual method for a while in the late 19th century before the advent of inexpensive autoclaves. Prolonged exposure to high energy radiation, such as x-rays X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3 × 1016 Hz to 3 × 1019 Hz) and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma rays. In many and gamma rays Gamma rays are electromagnetic radiation of high frequency (very short wavelength). They are produced by sub-atomic particle interactions such as electron-positron annihilation, neutral pion decay, radioactive decay, fusion, fission or inverse Compton scattering in astrophysical processes. Gamma rays typically have frequencies above 1019 Hz, and, will also kill most endospores.

Reactivation

Reactivation of the endospore occurs when conditions are more favourable and involves activation, germination, and outgrowth. Even if an endospore is located in plentiful nutrients, it may fail to germinate unless activation has taken place. This may be triggered by heating the endospore. Germination involves the dormant endospore starting metabolic activity and thus breaking hibernation. It is commonly characterised by rupture or absorption of the spore coat, swelling of the endospore, an increase in metabolic activity, and loss of resistance to environmental stress. Outgrowth follows germination and involves the core of the endospore manufacturing new chemical components and exiting the old spore coat to develop into a fully functional vegetative bacterial cell, which can divide to produce more cells.

Importance

As a simplified model for cellular differentiation In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of tissues and cell types. Differentiation is a common, the molecular details of endospore formation have been extensively studied, specifically in the model organism A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. In particular, model organisms are widely used to explore potential causes and treatments for human disease Bacillus subtilis Bacillus subtilis, known as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate extreme environmental conditions. Unlike several other well-. These studies have contributed much to our understanding of the regulation of gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as rRNA genes or tRNA genes, the product is a functional RNA. The process of gene expression is used by all known life - eukaryotes , prokaryotes (bacteria, transcription factors In the field of molecular biology, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the transfer (or transcription) of genetic information from DNA to mRNA. Transcription factors perform this function alone or with other proteins in a complex, by promoting (as an activator), or blocking (as a repressor), and the sigma factor A sigma factor is a prokaryotic transcription initiation factor that enables specific binding of RNA polymerase to gene promoters. Different sigma factors are activated in response to different environmental conditions. Every molecule of RNA polymerase contains exactly one sigma factor subunit, which in the model bacterium Escherichia coli is one subunits of RNA polymerase RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses. In chemical terms, RNAP is a nucleotidyl transferase that polymerizes ribonucleotides at the 3'.

Endospores of the bacterium Bacillus anthracis Bacillus anthracis is a Gram-positive spore-forming, rod-shaped bacterium, with a width of 1-1.2µm and a length of 3-5µm. It can be grown in an ordinary nutrient medium under aerobic or anaerobic conditions[citation needed]. It is the only bacterium with a protein capsule , and the only pathogenic bacteria to carry its own adenylyl cyclase were used in the 2001 anthrax attacks The 2001 anthrax attacks in the United States, also known as Amerithrax from its Federal Bureau of Investigation case name, occurred over the course of several weeks beginning on September 18, 2001, only a few days after the September 11 attacks. Letters containing anthrax spores were mailed to several news media offices and two Democratic U.S. The powder found in contaminated postal letters was composed of extracellular anthrax endospores. Inhalation, ingestion or skin contamination of these endospores, which were technically incorrectly labelled as "spores", led to a number of deaths.

Geobacillus stearothermophilus Bacillus stearothermophilus is a rod-shaped, Gram-positive bacterium and a member of the division Firmicutes. The bacteria is a thermophile and is widely distributed in soil, hot springs, ocean sediment, and is a cause of spoilage in food products. It will grow within a temperature range of 30-75 degrees celsius. It is commonly used as a challenge endospores are used as biological indicators when an autoclave is used in sterilization procedures.

Endospore-forming bacteria

Examples of endospore-forming bacteria include the genera:

• Acetonema Acetonema is a genus of bacteria in the family Veillonellaceae. It is H2-oxidizing CO2-reducing acetogenic strictly anaerobic endospore-forming Gram-negative motile rod-shaped, isolated from gut contents of the wood-feeding termite Pterotermes occidentis. Cells are catalase positive, oxidase negative, and have 51.5 mol percent G + C in their DNA
• Alkalibacillus
• Ammoniphilus
• Amphibacillus
• Anaerobacter
• Anaerospora
• Aneurinibacillus
• Anoxybacillus
• Bacillus
• Brevibacillus
• Caldanaerobacter
• Caloramator
• Caminicella
• Cerasibacillus
• Clostridium
• Clostridiisalibacter
• Cohnella
• Dendrosporobacter
• Desulfotomaculum
• Desulfosporomusa
• Desulfosporosinus
• Desulfovirgula
• Desulfunispora
• Desulfurispora
• Filifactor
• Filobacillus
• Gelria
• Geobacillus
• Geosporobacter
• Gracilibacillus
• Halonatronum
• Heliobacterium
• Heliophilum
• Laceyella
• Lentibacillus
• Lysinibacillus
• Mahella
• Metabacterium
• Moorella
• Natroniella
• Oceanobacillus
• Orenia
• Ornithinibacillus
• Oxalophagus
• Oxobacter
• Paenibacillus
• Paraliobacillus
• Pelospora
• Pelotomaculum
• Piscibacillus
• Planifilum
• Pontibacillus
• Propionispora
• Salinibacillus
• Salsuginibacillus
• Seinonella
• Shimazuella
• Sporacetigenium
• Sporoanaerobacter
• Sporobacter
• Sporobacterium
• Sporohalobacter
• Sporolactobacillus
• Sporomusa
• Sporosarcina
• Sporotalea
• Sporotomaculum
• Syntrophomonas
• Syntrophospora
• Tenuibacillus
• Tepidibacter
• Terribacillus
• Thalassobacillus
• Thermoacetogenium
• Thermoactinomyces
• Thermoalkalibacillus
• Thermoanaerobacter
• Thermoanaeromonas
• Thermobacillus
• Thermoflavimicrobium
• Thermovenabulum
• Tuberibacillus
• Virgibacillus
• Vulcanobacillus

References

1. ^ endospore at Dorland's Medical Dictionary
2. ^ Prescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3.

External links

• Endospore structure
• Endospore Structure 2
• Microbial Spore Formation
• Malachite green - endospore staining technique (video)

Categories: Microbiology | Bacteriology

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