Agrowth medium orculture medium is a solid, liquid, or semi-solid designed to support the growth of a population ofmicroorganisms orcells via the process ofcell proliferation[1] or smallplants like themossPhyscomitrella patens.[2] Different types of media are used for growing different types of cells.[3]
The two major types of growth media are those used forcell culture, which use specific cell types derived from plants or animals, and those used formicrobiological culture, which are used for growing microorganisms such asbacteria orfungi. The most common growth media for microorganisms are nutrient broths andagar plates; specialized media are sometimes required for microorganism and cell culture growth.[1] Some organisms, termedfastidious organisms, require specialized environments due to complex nutritional requirements.Viruses, for example, are obligate intracellularparasites and require a growth medium containing living cells.
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The most common growth media for microorganisms are nutrient broths (liquid nutrient medium) orlysogeny broth medium. Liquid media are often mixed withagar and poured via a sterilemedia dispenser intoPetri dishes to solidify. Theseagar plates provide a solid medium on which microbes may be cultured. They remain solid, as very few bacteria are able to decompose agar (the exception being some species in the genera:Cytophaga,Flavobacterium,Bacillus,Pseudomonas, andAlcaligenes). Bacteria grown in liquid cultures often formcolloidalsuspensions.[4][5]
The difference between growth media used for cell culture and those used for microbiological culture is that cells derived from whole organisms and grown in culture often cannot grow without the addition of, for instance,hormones orgrowth factors which usually occurin vivo.[6] In the case of animal cells, this difficulty is often addressed by the addition ofblood serum or a synthetic serum replacement to the medium. In the case of microorganisms, no such limitations exist, as they are oftenunicellular organisms. One other major difference is that animal cells in culture are often grown on a flat surface to which they attach, and the medium is provided in a liquid form, which covers the cells. In contrast, bacteria such asEscherichia coli may be grown on solid or in liquid media.
An important distinction between growth media types is that ofchemically defined versus undefined media.[1] A defined medium will have known quantities of all ingredients. For microorganisms, they consist of providing trace elements and vitamins required by the microbe and especially definedcarbon andnitrogen sources.Glucose orglycerol are often used as carbon sources, andammoniumsalts ornitrates asinorganic nitrogen sources. An undefined medium has some complex ingredients, such asyeast extract or casein hydrolysate, which consist of a mixture of many chemical species in unknown proportions. Undefined media are sometimes chosen based on price and sometimes by necessity – some microorganisms have never been cultured on defined media.
A good example of a growth medium is thewort used to makebeer. The wort contains all the nutrients required for yeast growth, and underanaerobic conditions, alcohol is produced. When thefermentation process is complete, the combination of medium and dormant microbes, now beer, is ready for consumption. The main types are
Culture media contain all the elements that most bacteria need for growth and are not selective, so they are used for the general cultivation and maintenance of bacteria kept in laboratory culture collections.
An undefined medium (also known as a basal or complex medium) contains:
This is an undefined medium because the amino-acid source contains a variety of compounds; the exact composition is unknown.
A defined medium (also known aschemically defined medium or synthetic medium) is a medium in which
Examples of nutrient media:
A defined medium that has just enough ingredients to support growth is called a "minimal medium". The number of ingredients that must be added to a minimal medium varies enormously depending on which microorganism is being grown.[7] Minimal media are those that contain the minimum nutrients possible for colony growth, generally without the presence of amino acids, and are often used by microbiologists and geneticists to grow "wild-type" microorganisms. Minimal media can also be used to select for or againstrecombinants orexconjugants.
Minimal medium typically contains:
Supplementary minimal media are minimal media that also contains a single selected agent, usually an amino acid or a sugar. This supplementation allows for the culturing of specific lines ofauxotrophic recombinants.
Selective media are used for the growth of only selected microorganisms. For example, if a microorganism is resistant to a certainantibiotic, such asampicillin ortetracycline, then that antibiotic can be added to the medium to prevent other cells, which do not possess the resistance, from growing. Media lacking an amino acid such asproline in conjunction withE. coli unable to synthesize it were commonly used by geneticists before the emergence ofgenomics tomap bacterial chromosomes.
Selective growth media are also used incell culture to ensure the survival or proliferation of cells with certain properties, such asantibiotic resistance or the ability to synthesize a certainmetabolite. Normally, the presence of a specificgene or anallele of a gene confers upon the cell the ability to grow in the selective medium. In such cases, the gene is termed amarker.
Selective growth media foreukaryotic cells commonly containneomycin to select cells that have been successfullytransfected with a plasmid carrying the neomycin resistance gene as a marker.Gancyclovir is an exception to the rule, as it is used to specifically kill cells that carry its respective marker, theHerpes simplex virus thymidine kinase.
Examples of selective media:
Differential or indicator media distinguish one microorganism type from another growing on the same medium.[12] This type of media uses the biochemical characteristics of a microorganism growing in the presence of specific nutrients or indicators (such asneutral red,phenol red,eosin y, ormethylene blue) added to the medium to visibly indicate the defining characteristics of a microorganism. These media are used for the detection of microorganisms and by molecular biologists to detect recombinant strains of bacteria.
Examples of differential media:
Transport media should fulfill these criteria:
Examples of transport media:
Enriched media contain the nutrients required to support the growth of a wide variety of organisms, including some of the more fastidious ones. They are commonly used to harvest as many different types of microbes as are present in the specimen.Blood agar is an enriched medium in which nutritionally rich whole blood supplements the basic nutrients.Chocolate agar is enriched with heat-treated blood (40–45 °C or 104–113 °F), which turns brown and gives the medium the color for which it is named.[citation needed]
The choice of culture medium might affect thephysiological relevance of findings fromtissue culture experiments, especially for metabolic studies.[15] In addition, the dependence of acell line on a metabolic gene was shown to be affected by the media type.[16] When performing a study involving several cell lines, utilizing a uniform culture media for all cell lines might reduce the bias in the generated datasets. Using a growth medium that better represents the physiological levels of nutrients can improve the physiological relevance ofin vitro studies and recently such media types, as Plasmax[17] and human plasma-like medium (HPLM),[18] were developed.
The selection of cell culture medium is crucial for efficient mammalian cell culture, significantly affecting cell growth, productivity, and consistency across batches.[19] In protein expression, the choice of media can also influence the therapeutic characteristics of produced proteins through processes like glycosylation.[20] Different types of media, such as serum-containing, serum-free, protein-free, and chemically defined media, have distinct benefits and drawbacks.
Serum-containing media are rich in growth factors but can lead to variability and contamination issues. Fetal bovine serum (FBS) is commonly used due to its high capacity to support cell growth, although it poses biosafety concerns due to its inconsistent composition.[19] In contrast, serum-free media (SFM) offer standardized formulations that enhance reliability and reduce contamination risks. They are designed to include essential nutrients like amino acids, vitamins, and glucose, but can sometimes provide weaker growth performance compared to serum-containing alternatives.[21] The development of protein-free and chemically defined media is aimed at achieving greater consistency and control in cell culture processes.
Ultimately, the composition of the culture medium directly impacts cell viability and productivity, making the careful selection and design of culture media essential for successful mammalian cell culture.[22]
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