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''Micrococcus'' (mi’ krō kŏk’ Əs) is a genus of bacteria in the
Micrococcaceae The family ''Micrococcaceae'' includes bacterial genera of Gram positive cocci that inhabit the air and skin, such as ''Micrococcus luteus''. Genera The family ''Micrococcaceae'' comprises the following genera: * '' Acaricomes'' Pukall ''et a ...
family. ''Micrococcus'' occurs in a wide range of environments, including water, dust, and soil. Micrococci have Gram-positive spherical cells ranging from about 0.5 to 3 micrometers in diameter and typically appear in tetrads. They are
catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting t ...
positive, oxidase positive,
indole Indole is an aromatic heterocyclic organic compound with the formula C8 H7 N. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indole is widely distributed in the natural environme ...
negative and
citrate Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...
negative. ''Micrococcus'' has a substantial
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering me ...
, which may comprise as much as 50% of the cell mass. The genome of ''Micrococcus'' is rich in
guanine Guanine () (symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is called ...
and
cytosine Cytosine () (symbol C or Cyt) is one of the four nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amin ...
(GC), typically exhibiting 65 to 75% GC-content. Micrococci often carry plasmids (ranging from 1 to 100 MDa in size) that provide the organism with useful traits. Some species of ''Micrococcus'', such as ''M. luteus'' (yellow) and ''M. roseus'' (red) produce yellow or pink colonies when grown on mannitol salt agar. Isolates of ''M. luteus'' have been found to overproduce riboflavin when grown on toxic organic pollutants like pyridine.
Hybridization Hybridization (or hybridisation) may refer to: *Hybridization (biology), the process of combining different varieties of organisms to create a hybrid *Orbital hybridization, in chemistry, the mixing of atomic orbitals into new hybrid orbitals *Nu ...
studies indicate that species within the genus ''Micrococcus'' are not closely related, showing as little as 50% sequence similarity. This suggests that some ''Micrococcus'' species may, on the basis of
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...
analysis, eventually be re-classified into other microbial genera.


Environmental

Micrococci have been isolated from human skin, animal and dairy products, and beer. They are found in many other places in the environment, including water, dust, and soil. ''M. luteus'' on human skin transforms compounds in sweat into compounds with an
unpleasant odor An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sense ...
. Micrococci can grow well in environments with little water or high salt concentrations, including
sportswear Sportswear or activewear is clothing, including footwear, worn for sport or physical exercise. Sport-specific clothing is worn for most sports and physical exercise, for practical, comfort or safety reasons. Typical sport-specific garments ...
made with synthetic fabrics. Most are
mesophile 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 ...
s; some, like ''Micrococcus antarcticus'' (found in Antarctica) are
psychrophile Psychrophiles or cryophiles (adj. ''psychrophilic'' or ''cryophilic'') are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from to . They have an optimal growth temperature at . They are found in ...
s. Though not a
spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
former, ''Micrococcus'' cells can survive for an extended period of time, both at refrigeration temperatures, and in nutrient-poor conditions such as sealed in
amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In Ma ...
.


Pathogenesis

''Micrococcus'' is generally thought to be a saprotrophic or
commensal organism Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fr ...
, though it can be an
opportunistic pathogen An opportunistic infection is an infection caused by pathogens (bacteria, fungi, parasites or viruses) that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune ...
, particularly in hosts with compromised immune systems, such as
HIV The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...
patients. It can be difficult to identify ''Micrococcus'' as the cause of an infection, since the organism is a normally present in skin microflora, and the genus is seldom linked to disease. In rare cases, death of immunocompromised patients has occurred from pulmonary infections caused by ''Micrococcus''. Micrococci may be involved in other infections, including recurrent bacteremia, septic shock, septic arthritis, endocarditis, meningitis, and cavitating pneumonia (immunosuppressed patients).


Industrial uses

Micrococci, like many other representatives of the Actinobacteria, can be catabolically versatile, with the ability to utilize a wide range of unusual substrates, such as pyridine, herbicides, chlorinated biphenyls, and
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
. They are likely involved in detoxification or biodegradation of many other environmental pollutants. Other ''Micrococcus'' isolates produce various useful products, such as long-chain (C21-C34) aliphatic hydrocarbons for lubricating oils.


References


External links


Microbewiki
at
Kenyon College Kenyon College is a private liberal arts college in Gambier, Ohio. It was founded in 1824 by Philander Chase. Kenyon College is accredited by the Higher Learning Commission. Kenyon has 1,708 undergraduates enrolled. Its 1,000-acre campus is s ...
{{Taxonbar, from=Q1954952 Micrococcaceae Bacteria genera