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A mesophile is an
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...
that grows best in moderate
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37°C. The term is mainly applied to
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
s. Organisms that prefer extreme environments are known as extremophiles. Mesophiles have diverse classifications, belonging to two
domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined ** Domain of definition of a partial function ** Natural domain of a partial function **Domain of holomorphy of a function * ...
s:
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
,
Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...
, and to kingdom
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
of domain Eucarya. Mesophiles belonging to the domain Bacteria can either be gram-positive or
gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...
. Oxygen requirements for mesophiles can be aerobic or anaerobic. There are three basic shapes of mesophiles:
coccus A coccus (plural cocci) is any bacterium or archaeon that has a spherical, ovoid, or generally round shape. Bacteria are categorized based on their shapes into three classes: cocci (spherical-shaped), bacillus (rod-shaped) and spiral ( of whi ...
, bacillus, and
spiral In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point. Helices Two major definitions of "spiral" in the American Heritage Dictionary are:cheese Cheese is a dairy product produced in wide ranges of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. During productio ...
and
yogurt Yogurt (; , from tr, yoğurt, also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial fermentation of milk. The bacteria used to make yogurt are known as ''yogurt cultures''. Fermentation of sugars in the milk by these bac ...
. They are often included during fermentation of
beer Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
and
wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different ...
making. Since normal human body temperature is 37
°C The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The d ...
, the majority of human pathogens are mesophiles, as are most of the organisms comprising the
human microbiome The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding anatomical sites in which they reside, including the skin, mammary glands, seminal fluid, uterus, ovarian ...
.


Mesophiles vs. extremophiles

Mesophiles are the opposite of
extremophile An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme tem ...
s. Extremophiles that prefer cold environments are termed psychrophilic, those preferring warmer temperatures are termed thermophilic or thermotropic and those thriving in extremely hot environments are
hyperthermophilic A hyperthermophile is an organism that thrives in extremely hot environments—from 60 °C (140 °F) upwards. An optimal temperature for the existence of hyperthermophiles is often above 80 °C (176 °F). Hyperthermophiles are often within the doma ...
. A genome-wide computational approach has been designed by Zheng, et al. to classify bacteria into mesophilic and thermophilic.


Adaptations

All bacteria have their own optimum environmental surroundings and temperatures in which they thrive. Many factors are responsible for a given organism's optimal temperature range, but evidence suggests that the expression of particular genetic elements ( lleles can alter the temperature-sensitive phenotype of the organism. A study published in 2016 demonstrated that mesophilic bacteria could be genetically engineered to express certain alleles from psychrophilic bacteria, consequently shifting the restrictive temperature range of the mesophilic bacteria to closely match that of the psychrophilic bacteria. Due to the less stable structure of mesophiles, it has reduced flexibility for
protein synthesis Protein biosynthesis (or protein synthesis) is a core biological process, occurring inside cells, balancing the loss of cellular proteins (via degradation or export) through the production of new proteins. Proteins perform a number of critical ...
. Mesophiles are not able to synthesize proteins in low temperatures. It is more sensitive to temperature changes, and the
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...
composition of the membrane does not allow for much fluidity. Decreasing the optimal temperature of 37 °C to 0 °C to 8 °C leads to a gradual decrease in protein synthesis. Cold-induced proteins (CIPs) are induced during low temperatures, which then allows cold-shock proteins (CSPs) to synthesize. The shift back to the optimal temperature sees an increase, indicating that mesophiles are highly dependent on temperature. Oxygen availability also affects microorganism growth. There are two explanations for thermophiles being able to survive at such high temperatures whereas mesophiles can not. The most evident explanation is that thermophiles are believed to have cell components that are relatively more stable than the cell components of mesophiles which is why thermophiles are able to live at higher temperatures than mesophiles. "A second school of thought, as represented by the writings of Gaughran (21) and Allen (3), believes that rapid resynthesis of damaged or destroyed cell constituents is the key to the problem of biological stability to heat."


Oxygen requirements

Due to the diversity of mesophiles, oxygen requirements greatly vary.
Aerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
requires the use of
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
and anaerobic does not. There are three types of anaerobes. Facultative anaerobes grow in the absence of oxygen, using
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
instead. During fermentation, sugars are converted to acids,
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
, or gases. If there is oxygen present, it will use aerobic respiration instead. Obligate anaerobes cannot grow in the presence of oxygen. Aerotolerant anaerobes can withstand oxygen.


Roles

Microorganisms play an important role in
decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and ...
of organic matter and
mineralization Mineralization may refer to: * Mineralization (biology), when an inorganic substance precipitates in an organic matrix ** Biomineralization, a form of mineralization ** Mineralization of bone, an example of mineralization ** Mineralized tissues ar ...
of
nutrients A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...
. In aquatic environments, the diversity of the
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
allows for the diversity of mesophiles. The functions of each mesophile rely on the surroundings, most importantly temperature range.
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
such as mesophiles and
thermophile A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...
s are used in the
cheesemaking Cheesemaking (or caseiculture) is the craft of making cheese. The production of cheese, like many other food preservation processes, allows the nutritional and economic value of a food material, in this case milk, to be preserved in concentr ...
due to their role in
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
. "Traditional
microbiologist A microbiologist (from Greek ) is a scientist who studies microscopic life forms and processes. This includes study of the growth, interactions and characteristics of microscopic organisms such as bacteria, algae, fungi, and some types of para ...
s use the following terms to indicate the general (slightly arbitrary) optimum temperature for the growth of bacteria: psychrophiles (15–20 °C),
mesophiles A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37°C. The term is mainly applied to microorganisms. Organi ...
(30–37 °C), thermophiles (50–60 °C) and extreme thermophiles (up to 122 °C)".Johnson, Mark. "Mesophilic and Thermophilic Cultures Used in Traditional Cheesemaking." Cheese and Microbes. Washington: ASM Publishing. 2014. Web. Both mesophiles and thermophiles are used in cheesemaking for the same reason; however, they grow, thrive and die at different temperatures. Psychrotrophic bacteria contribute to dairy products spoiling, getting mouldy or going bad due to their ability to grow at lower temperatures such as in a refrigerator.


Examples

Some notable mesophiles include '' Listeria monocytogenes'', ''
Staphylococcus aureus ''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often posit ...
'', and ''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
''. Other examples of
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
of mesophiles are ''
Clostridium kluyveri ''Clostridium kluyveri'' (CLOKL) is an anaerobic, motile, gram-positive bacterium In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteri ...
'', ''
Pseudomonas maltophilia '' Stenotrophomonas maltophilia'' is an aerobic, nonfermentative, Gram-negative bacterium. It is an uncommon bacterium and human infection is difficult to treat. Initially classified as ''Bacterium bookeri'', then renamed ''Pseudomonas maltophi ...
'', '' Thiobacillus novellus'', '' Streptococcus pyogenes'', and '' Streptococcus pneumoniae''. Different types of diseases and infections typically have pathogens from mesophilic bacteria such as the ones listed above.


''Listeria monocytogenes''

''Listeria monocytogenes'' is a gram-positive bacterium. It is closely related to ''Bacillus'' and ''Staphylococcus''. It is a rod-shaped, facultative anaerobe that is motile by peritrichous
flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...
. ''L. monocytogenes'' motility is limited from 20 °C to 25 °C. At the optimal temperature, it loses its motility. This bacterium is responsible for listeriosis which derives from contaminated food.Magalhã£Es, R. (2014). Listeria monocytogenes. 450-461.


''Staphylococcus aureus''

''Staphylococcus aureus'' was first identified in 1880. It is responsible for different infections stemming from an injury. The bacterium overcomes the body's natural mechanisms. Long lasting infections of ''S. aureus'' includes
pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severit ...
,
meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...
, and osteomyelitis. ''S. aureus'' is commonly contracted in hospital settings.Todd, E. (2014). Staphylococcus Aureus. 530-534


''Escherichia coli''

''Escherichia coli'' is a gram-negative, rod-shaped facultative anaerobic bacterium that does not produce spores. The bacterium is a member of
Enterobacteriaceae Enterobacteriaceae is a large family of Gram-negative bacteria. It was first proposed by Rahn in 1936, and now includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject of debate, but o ...
. It is capable of producing enterotoxins which are thermolabile or thermostable.Robinson, Richard K.. (2000). Encyclopedia of Food Microbiology, Volumes 1-3 - Escherichia Coli. Elsevier. Online version available at: http://app.knovel.com/hotlink/pdf/id:kt0051LGG3/encyclopedia-food-microbiology/escherichia-coli Other characteristics of ''E. coli'' are that it is oxidase-negative, citrate-negative, methyl-red positive, and Voges-Proskauer-negative. To sum up ''E. coli'', it is a coliform. It is able to use
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
and
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...
as a carbon source for fermentation. ''E. coli'' is commonly found in the gut of living organisms. ''E. coli'' has many capabilities such as being a host for
recombinant DNA Recombinant DNA (rDNA) molecules are DNA molecules formed by laboratory methods of genetic recombination (such as molecular cloning) that bring together genetic material from multiple sources, creating sequences that would not otherwise be f ...
and being a pathogen.Robinson, Richard K.. (2000). Encyclopedia of Food Microbiology, Volumes 1-3 - Escherichia Coli. Elsevier. Online version available at: http://app.knovel.com/hotlink/pdf/id:kt0051K7I1/encyclopedia-food-microbiology/ecology-bacteria-escherichia-3


See also

*
Anaerobic digestion Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the ferm ...
*
Mesophilic digester Mesophilic digester or Mesophilic biodigester is a kind of biodigester that operates in temperatures between 20 °C and about 40°, typically 37 °C. This is the most used kind of biodigester in the world. More than 90% of worldwide biodig ...
* Mesophyte * Neutrophile * Reverse ecology


References

{{Reflist Anaerobic digestion Biodegradable waste management Biodegradation Microbial growth and nutrition