Expression Technologies Inc.

Bacterial E.coli Growth Media

Section list of bacterial E.coli growth media

Properties of Bacterial E.coli growth media

Solid vs. liquid growth media

Escherichia coli or E.coli cells may grow on a solid or in a liquid growth medium under a laboratory condition. Solid and liquid media may have exactly the same composition except that the solid medium contains an extra 1.5% agar. Different E.coli clones may have different properties. Colonies growing on solid media represent different clones. These colonies are used for clone selection in DNA cloning and protein expression in molecular biology studies. A selected E.coli clone can be grown in a large quantity in a liquid medium. A liquid medium is often used for plasmid DNA and recombinant protein production. E.coli cells have different growth properties on solid or in liquid media even though they have the same composition except agar. For example, E.coli cells can grow on a solid medium plate at pH 11, but they cannot grow in a liquid media with pH 9 or higher. All growth conditions discussed below are related only to liquid media unless otherwise noted.

E.coli cell growth curve, growth phases and their biochemical applications

E.coli cells grow differently under different conditions. The E.coli cell density after inoculation can be graphically described as growth curves. The growth curve is comprised of four major phases: lag phase, log phase, stationary phase, and death phase. At the lag phase, the cell density increases slowly. The lag phase can be clearly observed if the cell culture is inoculated from a single colony on a old plate or from a small volume of a cell stock. The lag phase is not obvious if the inoculation is from a fresh culture with relatively large volumes at 1:50 or 1:100 inoculations. In these cases, E.coli cells grow directly into the log phase.
The log phase is also called the exponential growth phase. At the log phase, E.coli cells grow rapidly or exponentially. The doubling time is often 20 to 30 minutes for most wild-type E.coli strains in a rich medium. The E.coli cells are healthy and are at the prime state to produce proteins at the early log phase. The E.coli cells are often harvested at the middle to late log phases for protein production. Harvesting cells later than the log phase may observe low protein yield and high protein degradation. E.coli cells at the early log phase are also used to make competent cells and cell stocks.
The stationary phase is also called the saturation phase or steady phase. At the stationary phase, the medium's nutrients become limited and metabolic products accumulate to such a high level that they are inhibitory to the cell growth. E.coli cells are stressed at this phase. The cell density is highest at the stationary phase (see figure bellow) and most E.coli strains appear to contain high amount of plasmids. Therefore the E.coli cells at the stationary phase are mostly used for plasmid production, but they are generally not good for protein production or other purposes.
The death phase is also known as the decline phase. At the death phase, nutrients become so limited and toxic metabolites are so high that the perished cells exceed newly formed cells and cell density decreases. E.coli cells at the death phase cannot be used to make competent cells or cell stocks. They are not good for plasmid or protein production. It is important not to grow the cells to the death phase for all biochemical applications.

Schematic E.coli cell growth curve

Under most laboratory conditions, E.coli cell growth often does not follow the growth curve above. For example, most scientists will not grow the cells to the death phase. This part of curve will not be observed for most studies. For protein productions, E.coli colonies are often inoculated into about 4 ml cultures, and these 4 ml cultures are freshly inoculated into larger cultures of 500 ml. Cell growth in these 500 ml cultures only presents log phase characters for protein production. The lag phase will not be observed in these cases.

E.coli cell growth curve
(for most plasmid or protein preps in a shake flask container)

The growth curve above is also simplified because E.coli cells grow slower after protein induction. E.coli cells may also grow slower when harboring some plasmids.

E.coli cell growth curve for protein prep
(Example: a maxi prep of 500 ml in a shake flask container)

E.coli cells with most plasmids and some proteins will follow curve A. Sometimes E.coli cells expressing some proteins will follow curve B. In these cases, the recombinant proteins interfere with cell proliferation and/or differentiation. These recombinant proteins are toxic to E.coli cells when over-expressed. E.coli cells with extremely toxic proteins will follow growth curve C. In such cases, both plasmid and protein production will be very low. Different technologies should be used to produce these plasmids or proteins. The slope of the growth curve will be different for E.coli cells containing different plasmids or expressing different recombinant proteins.

E.coli OD600, wet weight, dry weight, cell volume, cell number and cell density

OD stands for optical density. The number following the OD indicates the wavelength of light. OD600, OD550, OD650 or other wave lengths may be used to estimate the E.coli cell density. OD600 is the most commonly used. OD600 measures the light absorbance of an E.coli cell culture sample. The OD600 value corresponds with the cell density or cell number in a given E.coli culture volume. Different cell strains may have different cell numbers at a given OD600 value, but OD600 = 1 usually means there are about 1 x 10⁹ cells per ml culture. Different growth conditions will also give different OD600 values.

OD600 is used to measure the E.coli cell density. The OD600 value is also an important indicator of the physiological condition of the E.coli cells in a given medium after a specific culture period. The OD600 value determines if the E.coli cells may be ready for making competent cells, cell stocks, induction, or for being harvested.

OD measurement is more accurate at values less than 0.5 for most spectrometers. For common medium this means 10 time dilution of the culture. For high density growth medium, this means 100 time dilution. Distilled or deionized water should be used as a blank and in dilution. Rich media often have color by themselves. OD measurement will not be accurate if a medium is used as a blank or in dilution.

OD600 may also be used to calculate E.coli cell weight. The E.coli cell wet weight is measured by the cell pellet weight after the centrifugation of a cell culture. Cell density at 1 x 10⁹ per ml usually gives about 1 mg/ml cells or 1 gram/liter wet cell weight. The E.coli dry cell weight is usually 25% or 1/4 of its wet cell weight. the average E.coli cell mass is about 1 pg/cell or 1 x 10^-12 g/cell wet weight. Different E.coli strains and growth conditions will present certain difference on these values. The differences in the values can be as much as a few times, but they are normally less than 10 times. The OD value of series dilution of E.coli cells may be plotted against the actual number of cells grown on a series of plates to generate a standard curve to get a relatively accurate estimation of cell density under normal growth conditions. However, accurate determinations of cell density may not be possible under extreme growth conditions since not all cells are viable under these conditions. Accurate determinations of cell numbers are not needed for most molecular biology experiments, such as determining inoculation volume, induction time, or harvesting time.

Scientists involved in large scale production often use wet or dry cell weights. Research scientists normally use OD600 or the cell number. The following equation may be used for a general estimation of cell density, number and weight.

OD600 = 1 ≈ 1 x 10⁹ cells/ml ≈ 1 mg/ml or 1 g/liter wet cell weight ≈ 1/4 g/liter or 0.25 g/liter dry cell weight

Research scientists often grow a few milliliters or hundreds of milliliters of cell cultures. Few scientists will weigh the cell pellets after harvesting. However cell pellets are often centrifuged in test tubes. The cell volume can often be easily observed in a test tube.

OD600 = 1 ≈ 1 x 10⁹ cells/ml culture ≈ 1 ul wet cell/ml culture or 1 ml wet cell/liter culture

The wet cell volume will be about 5 ml if the OD600 of a 500 ml culture is 10. A large volume of a cell pellet will indicate a high OD600 value of the culture. Wet cell volume can often be used to estimate the cell density without reading its OD600.

Trace metals, minerals, and vitamins in E.coli growth media

E.coli cells are what they eat and grow on. The E.coli growth medium is not only the food for E.coli cells but is also their habitat. The growth medium, medium container, aeration condition, and growth temperature form the E.coli cell growth ecosystem in a lab. One of the most important reasons that recombinant proteins are more soluble and active when expressed in insect cells and mammalian cells is their growth media. Insect and mammalian cells normally grow in serum-based media. Animal sera contain many nutrients needed for animal cell growth. These nutrients include many trace metals, minerals, and vitamins, which may serve as prosthetic groups, co-factors or ligands for recombinant proteins. E.coli cells can synthesize most of its nutrients and may not need them for their growth. However, only in the presence of these prosthetic groups, co-factors, or ligands will many recombinant proteins be expressed soluble, stable and functional in E.coli cells. The growth medium and culture conditions also determine the quantity of E.coli cells that may be obtained from a culture. Plasmid and protein yields are proportional to E.coli cell quantity. Therefore, the growth medium is one of the most important factors in determining the plasmid and protein yields. The growth medium may also determine the solubility, stability and activity of a recombinant protein.

Medium pH range and E.coli cell growth

In addition to nutrients, the pH of the growth medium is also important for E.coli growth rate and cell density. The optimal growth pH for E.coli is near neutral. E.coli cells can grow reasonably well over a range of three pH units (from pH 5.5 to 8.5). Extreme pH beyond this range will significantly decrease the cell growth rate and may sometimes even cause cell death. The minimum and maximum growth pHs for E.coli are pH 4.4 and 9.0 respectively. E.coli cells appear to tolerate a low pH better than a high pH. In fact, extended exposure of E.coli cells to a high pH causes cell lysis. At the saturation or stationary phase, the pH of the E.coli culture in commonly used media is near its pH limits. pH is another limiting factor for cell growth in addition to nutrition exhaustion and accumulation of toxic metabolites. The medium's pH is determined by medium compositions, buffers, cellular metabolites, and aeration conditions. Some common media such as TB use a phosphate buffer. Phosphate buffer capacity will be quickly exhausted at a high cell density (OD600 > 10). Organic salts such as sodium succinate and mono-sodium glutamate (MSG) and their acids may be used as buffers. After exhaustion these organic buffers, the medium reaches the E.coli cells' maximum pH limit. E.coli cells can also use sugars such as glycerol and glucose as carbon or energy sources. When the E.coli cells use these sugars as carbon sources, they will produce acetic acid and therefore lower the medium pH. Carefully balancing the phosphate buffer, organic buffers, sugar contents, and aeration conditions can maintain the culture medium pH near E.coli optimum growth pH or within the range of the three pH units. Low aeration conditions lead the cells to produce acids. High aeration conditions allow the cells to use organic acids as carbon source and increase medium pH. Selected aeration conditions can also help cells maintain its medium pH.

E.coli medium pH verses cell growth, viability, stock, plasmid production, and protein expression

The medium's pH also affects the E.coli cells' viability, stock, plasmid production, and protein expression. The optimal pH is almost always near neutral pH 7. Acidic pH is often better tolerated by E.coli cells than basic pH. These pH ranges are summarized in the following table and diagram, but there is always an exception for a particular cell strain, plasmid, or protein.

Aeration or oxygen O2 concentration in E.coli growth media

E.coli cells produce large quantities of acetic acid if the growth medium contains little or no oxygen causing the growth medium to reach pH 4 or lower. At this pH, E.coli cell growth slows down or even stops. Ampicillin will be Chemically degraded at low pH and the E.coli cells will partially or completely lose selection. The plasmid or protein production will be low because most cells do not contain the selected plasmid. Acetic acid is the major metabolic inhibitor under anaerobic growth condition. However, with proper aeration, E.coli cells will be able to use many organic acids as carbon sources and the pH of the growth medium will be maintained at near neutral or basic ranges. Aeration is another important factor in determining E.coli cell growth.

Medium agitation and E.coli cell growth

Agitation and aeration are closely related for most shake flasks under regular laboratory settings. Agitation is control by the shaking speed in revolutions per minute (rpm) of a shaker incubator. The higher the shaking speed (rpm), the better the agitation and aeration, provided that the container permits sufficient air exchange. Tightly fitting of the container to the container holder is also important for good aeration. The shaker incubator and incubation room should also be sufficiently ventilated to allow good aeration. If the container cover does not allow sufficient air exchange, the ventilation fan of the shaker incubator is malfunctioning, or the incubation room is not ventilated, higher agitation will not result in higher aeration. In these cases, E.coli cells will grow anaerobically and the growth medium will soon become acidic. Agitation alone without increasing aeration will still lead higher growth rate for E.coli cells, presumably because agitation increases metabolic exchange of the cells with the medium.

Temperature and E.coli growth

The natural environment of E.coli cells is the lower intestine of a warm-blooded animal. Its optimal growth temperature is 37 ⁰C. The doubling time or generation time for most E.coli strains in a rich medium at 37 ⁰C is between 20 to 40 minutes. E.coli cells cannot grow well at temperatures higher than 42 ⁰C. They can tolerate lower temperatures with lower growth rate. Protein synthesis slows at temperatures lower than 37 ⁰C. It is also observed that inclusion body accumulation is decreased and more soluble recombinant proteins are produced at lower temperatures. Temperatures from 15 to 30 degrees are often used to produce soluble proteins. In most cases, the temperature set on the incubator is the E.coli growth temperature. The E.coli growth temperature will have some delay when the medium is kept at 4 ⁰C or shifted from 37 ⁰C to a lower temperature. This delay should be taken into consideration for short protein inductions.

Osmolarity and E.coli growth media

The concentrations of nutrients and chemicals in the medium determine the medium osmolarity. A careful balance of nutrient and chemical contents will maintain the medium osmolarity optimal for E.coli growth. E.coli cells can grow on wide range of nutrient concentrations. However, different E.coli cell strains do exhibit different optimal nutrient requirements. Commonly used medium components such as peptone, yeast extract, and sodium chloride, when reaching certain high concentrations, may inhibit E.coli cell growth. This is true for all other supplement nutrients, including sugars and buffers. In addition, high nutrient concentration may also cause precipitation.

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Commonly used bacterial E.coli growth media
LB vs. SOB, SOC, 2x YT, Terrific Broth (TB), and Super Broth (SB)

LB broth (Luria broth, Luria-Bertani medium, or lysogeny broth) is the most commonly used medium in molecular biology for E.coli cultures. Easy to make, fast growth rate for most E.coli strains, readily available and simple compositions make LB the most popular medium. LB contains the enzymatic digestion product of casein commonly known as peptone (some vendors call it Tryptone), yeast extract, and sodium chloride. Peptone is casein digested by pepsin and Tryptone is casein digested by trypsin. We do not observe significant difference between these two casein digestions in E.coli cultures. Peptone is rich in amino acids and peptides. Its amino acid and peptide compositions reflect those of casein. In addition to amino acids and peptides, yeast extract also contains nucleic acids, lipids and other nutrients which are essential to E.coli cell growth. LB can support E.coli growth OD600 2 to 3 under normal shaking incubation conditions (250 rpm). LB Miller Broth and LB Lennox Broth contain higher and lower sodium chloride levels respectively. There are minimal differences between the two formulations in most molecular biology studies with commonly used E.coli strains. Different bacteria strains may require different salt concentrations. A low salt formula is more often used in salt-sensitive antibiotic selections. Buy LB broth... >

SOB medium (Super Optimal Broth or Hanahan's broth) is another commonly used rich medium. SOB has twice as much peptone as LB. SOB is richer in amino acids and peptides. In addition, SOB contains magnesium which is required for high density cell growth. SOB can support E.coli growth to OD600 3 to 5 under normal shake flask conditions (250 rpm). SOB can support cell density to OD600 10 to 15 with increased aeration (350 rpm). E.coli cells growing in SOB will have a higher transformation efficiency than those in LB medium. Buy SOB Medium... >

SOC medium (Super Optimal broth with Catabolic repressor) is the same as SOB with exception that it contains 20 mM glucose. Here, glucose serves as a catabolic repressor. Cells prefer to use glucose as carbon or energy source. In the presence of glucose, cellular machineries using other sugars will be repressed. At a concentration of 20 mM or 0.36%, it provides sufficient transcription repression for lacI repressed promoters at low cell density. Expression of recombinant protein that may adversely affect host cell physiology is repressed. As a result, transformation reactions using SOC to grow the cells for one hour will have a higher efficiency than those using LB. When SOC is not available, adding 20 mM glucose to LB or other commonly used media will result in a similar transformation efficiency as that of using SOC. Buy SOC medium... >

2x YT medium (2x Yeast extract and Tryptone) is named in comparing its nutrition contents with that of LB broth. It does have 2x as much yeast extract compared to LB, but it only has 60% (not exactly 2x) more peptone. Basically 2x YT is a richer medium than LB and can support a higher cell density and longer growth period for E.coli. 2x YT was originally formulated for growth and maintenance of E.coli and its fibrous bacteriophages, such as M13 phage. It allows relatively a large quantity of phage production without exhausting the nutrients. Buy 2x YT medium... >

TB medium (Terrific Broth) is a phosphate buffered rich medium. In addition to 20% more peptone and 380% more yeast extract than in LB, TB also has 0.4% glycerol as an extra carbon source. All these nutrients in TB can support E.coli growth to OD600 5 to 8 under normal shaking incubation conditions. Buy TB medium... >

SB medium (Super Broth) has 220% more peptone and 300% more yeast extract than LB. Therefore SB is super rich in peptone and yeast extract. We estimated that the major nutrients in peptone and yeast extract are still in excess well after cells reach saturation while trace nutrients are depleted in the same culture. Many scientists use SB for plasmid or protein production. Buy SB medium... >

Nutrient contents in commonly used bacterial E.coli growth media

Peptone or Tryptone: Peptone is casein digested by pepsin and Tryptone is casein digested by trypsin. We do not observe significant difference between these two casein digestions in E.coli cultures. This nutrients is made from the enzymatic digestion of cow milk protein casein. Its amino acid composition reflects those of casein. Different preps from different vendors may contain different amounts of lactose. They are generally exchangeable in E.coli cell growth and plasmid production. They may exhibit differences in protein expression because of lactose contents.
Yeast extract: Yeast extract is made from hydrolysate of yeast cells. It is rich in amino acids, lipids, and B vitamins. Trace metals and minerals contained in yeast extract are often insufficient for recombinant protein over-expression.
Sodium chloride: Sodium chloride is mainly used to maintain medium osmolarity.
Magnesium Mg2+ (in SOB): Magnesium Mg2+ is required for cellular enzymatic reactions. Adding Mg2+ in the medium will increase the cell density with increased aeration.
Potassium K+ (in SOB): Potassium K+ is used as a potassium source.
Phosphate (in TB): Phosphate is used as a buffer and phosphate source.
Glycerol (in TB): Glycerol is used as a carbon source.
Glucose (in SOC): Glucose is the preferred carbon source for E.coli cells. Other sugars will not be used in the presence of glucose. Therefore protein induction by IPTG, lactose or any other sugars cannot be achieved in the presence of glucose.

Aeration and E.coli cell density in commonly used growth media

Cell densities in all common media will be enhanced by increasing aeration. In fact, increasing aeration alone will increase E.coli cell density significantly. For example, the E.coli cell density in LB can reach OD600 up to 8 at 400 rpm in a shake flask container. There are two problems associated with the E.coli cells when they reach OD600 > 8 in LB. The first problem is high medium pH at > 8.5. At this or a higher pH, the ability of E.coli cells to produce protein is poor. The second problem is that the cells grow very fast. E.coli cells reach the highest cell density in a short period of time. Induction for protein expression can be difficult to control at a fast cell growth rate.

Mg2+ and E.coli cell density in commonly used growth media

Mg2+ is required for E.coli cell growth. However, Mg2+ alone will not increase cell density. It must be combined with better aeration conditions at higher shaking speeds for shake flask containers. Final magnesium concentration of 10 mM will increase cell density at a higher shaking speed (at about 350 rpm). The SOB medium contains a sufficient amount of magnesium. Good aeration alone will increase cell density for the SOB medium. Mg2+ plus a high shaking speed will increase the E.coli cell density in all commonly used media.

Applications of commonly used growth media LB, SOB, SOC, 2x YT, Terrific Broth (TB), and Super Broth (SB)

LB broth is mostly used for E.coli cell growth and propagation. LB broth is also commonly used for plasmid DNA and protein production at a laboratory scale. The yield and reproducibility of the LB broth is satisfactory for the mini prep, medium prep, and large prep of many plasmids and some proteins. LB agar (15%) is regularly used for E.coli colony selections. Some E.coli strains may grow better in low salt LB Lennox broth.

SOB medium is commonly used to make high-efficiency competent cells.

SOC medium is commonly used in the incubation after the heat-shock in the transformation reaction. When SOC is not available, adding 20 mM glucose to LB or other commonly used media will result in a similar transformation efficiency as compared to using SOC.

2x YT broth was originally formulated for the growth and maintenance of E.coli and its fibrous bacteriophages such as M13 phage. It allows a relatively large quantity of phage production without exhausting the host.

TB medium is mostly used for protein production in a laboratory scale. Some scientists also use TB for plasmid DNA production.

SB medium is mostly used for plasmid DNA production. Some scientists also use SB for protein production in a laboratory scale.

Disadvantages of commonly used media and needs for High density growth media

None of the general media can support E.coli growth to a cell density of OD600 to 10 or more in a shake flask under normal conditions (250 rpm). Therefore, the plasmid or protein yields in these media are relatively low. In addition, the buffers, if present in the medium, will be exhausted when cell growth reaches saturation. The pH of the cultures using these media will drop to 4 to 5 upon saturation under common conditions (250 rpm). At a low pH, antibiotics such as ampicillin will be chemically degraded. Degradation of ampicillin will cause partial or no selection of the cells. Under these conditions, 80% of the total cell population may not contain the intended plasmid. The plasmid yield is significantly lower than it should be. Cells cannot be induced to express the target protein when their densities are near saturation. Furthermore, nutrients, especially critical ones, are exhausted or depleted at or near cell saturation. Nutrition exhaustion can force the cells to recycle some of the cellular components (such as proteins) in order to survive. As a result, the induced protein may be severely degraded after the medium reaches saturation.

Commonly used growth media cannot reach a cell density of OD600 >20, even with added magnesium and increased aeration. Relatively low cell density in commonly used media limits plasmid and protein yields. Some commonly used media, such as TB, can reach OD600 = 15 with added magnesium and increased aeration (OD600 = 8 for LB). However the time window to express proteins for TB at these cell density is short. Some medium nutrients and buffer capacities are quickly exhausted at this cell density. We estimated that the time window for expressing protein in TB is less than three hours and that in LB is less than one hour at their respective highest cell density. This short time window is not useful for most recombinant protein expression. In addition, recombinant proteins may have solubility, stability, and activity problems in common media because they lack a sufficient amount of required trace metals, minerals, or vitamins. It will be useful if the proprietarily formulated media can reach a cell density of OD600 = 30 to 50, similar to that which can be reached in a fed-batch fermentor. At the same time, the time window to express protein can be extended. The plasmid and protein yields should be increased accordingly. In addition, all known trace metals, minerals, and vitamins as well as unknown factors in animal serum supplemented in the high density growth media should also help the solubility, stability and activity of expressed recombinant proteins.

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High density bacterial E.coli growth media
DNAGro^TM, ProGro^TM, AutoX^TM, DetoX^TM, InduX^TM, and SecPro^TM media

DNAGro^TM growth medium

For any given plasmid (copy number of the plasmid is determined), there are two ways to increase plasmid yield. The first way is to increase the cell density or the number of cells. The other way is to increase the percentage of cells containing the plasmid. Adding chloramphenicol to the medium may amplify some plasmids but not others. E.coli growth medium DNAGro^TM is proprietarily formulated for plasmid DNA and phage production. Most commonly-used E.coli strains can reach OD600 = 30 in a shake flask container in this  medium. Recombinant protein cannot be expressed in this medium because the medium composition inhibits protein induction by IPTG, arabinose, or any sugar-based inductions. Protein induction may be achieved in this medium if heat or salt inducible promoters are used. Ten times or higher cell density may be obtained from this medium when compared to that from LB broth when growth conditions are closely followed. Plasmid or phage DNA yields will increase accordingly if there is sufficient selection. Buy DNAGro^TM medium... >

ProGro^TM growth medium

E.coli growth medium ProGro^TM is proprietarily formulated for recombinant protein production. Most commonly used E.coli strains can reach OD600 = 30 in a shake flask container in this  medium. Recombinant proteins can be expressed in this medium regardless whether they are induced by IPTG, sugar, heat or salt. Ten times or higher cell density may be obtained in this medium than that from LB broth when growth conditions are closely followed. Recombinant protein yield will increase accordingly if there is sufficient selection. This growth medium contains trace metals, mineral, and vitamins that may be needed for solubility, stability, and activity of a recombinant protein. Buy ProGro^TM medium... >

AutoX^TM growth medium

E.coli growth medium AutoX^TM is proprietarily formulated for recombinant protein production. Most commonly used E.coli strains can reach OD600 = 30 in a shake flask container in this  medium. Recombinant proteins can be automatically expressed in this medium if they are induced by IPTG. Induction occurs after cell density reaches OD600 = 10. A specific inducer must be added if the recombinant protein is not induced by IPTG or lactose. Cell density ten times or higher may be obtained in this medium when compared to that from LB broth when growth conditions are closely followed. Recombinant protein yield will increased accordingly if there is sufficient selection. This growth medium contains trace metals, mineral, and vitamins that may be needed for solubility, stability, and activity of a recombinant protein. Buy AutoX^TM medium... >

DetoX^TM growth medium

DetoX^TM E.coli growth medium is proprietarily formulated for toxic protein production. Most commonly used E.coli strains can reach OD600 = 30 in a shake flask container in this  medium. This medium is designed for E.coli cell growth and propagation, but not for recombinant protein expression or production. The inhibitors in this medium will prohibit protein expression induced by IPTG, lactose, arabinose, or any other sugars. After cells reach inducible OD (5 to 20 for most cell strains or recombinant proteins), other high density growth media such as InduX^TM or ProGro^TM should be transferred to the cell pellet and induction may be performed in these media instead. Using common bacterial growth medium such as LB will result in lower yield. The medium has no effect on protein expression induced by heat or salt. This growth medium contains trace metals, mineral, and vitamins that may be needed for solubility, stability, and activity of a recombinant protein. Buy DetoX^TM medium... >

InduX^TM growth medium

InduX^TM E.coli growth medium is proprietarily formulated for recombinant protein production. Most commonly used E.coli strains can reach OD600 = 30 in a shake flask container in this medium. Recombinant proteins can be expressed in this medium regardless whether they are induced by IPTG, any other sugars, heat or salt. Ten times or higher cell density may be obtained in this medium than that from LB broth when growth conditions are closely followed. Recombinant protein yield will increase accordingly if there is sufficient selection. No IPTG is needed if the recombinant protein is induced by IPTG or lactose. A specific inducer must be added at induction if the protein is not induced by IPTG or lactose. This growth medium contains trace metals, mineral, and vitamins that may be needed for solubility, stability, and activity of a recombinant protein. Buy InduX^TM medium... >

SecPro^TM growth medium

SecPro^TM E.coli growth medium is proprietarily formulated for secretory protein expression. Most commonly used E.coli strains can reach OD600 = 20 in a shake flask container in this  medium. Recombinant proteins can be expressed in this medium regardless whether they are induced by IPTG, any other sugars, heat or salt. Ten times or higher cell density may be obtained in this medium when compared to that from LB broth when growth conditions are closely followed. Secretory protein expression will increase one hundred times or more. This growth medium contains trace metals, mineral, and vitamins that may be needed for solubility, stability, and activity of a recombinant protein. Some mutant cell strains or strains with toxic proteins do not grow well in this medium. In these cases, these cell strains should be grown in DetoX^TM or ProGro^TM medium first to reach inducible OD. Then change the medium to SecPro^TM for induction. Buy SecPro^TM medium... >

Nutrient contents in high density growth media

The exact formula of high density growth media are proprietary. In general, the high density growth media contain all the nutrients in commonly-used growth media. In addition, they contain trace metals, minerals, vitamins, and animal serum. These chemicals may serve as prosthetic groups, co-factors or ligands for recombinant proteins to increase protein solubility, stability, and activity. The high density growth media also contain phosphate and organic buffers which maintain the medium pH near optimal at high cell density for E.coli growth. Furthermore the high density growth media contain different sugars as carbon or energy sources for high density cell growth.

Aeration and E.coli cell density in high density growth media

These media are designed for high density E.coli cell growth with good aeration. E.coli cells need oxygen to grow to high cell density. Without oxygen, E.coli cells will produce large quantity of acids which will inhibit cell growth. The oxygen needs for high density growth media are more than those of commonly used media. We recommend the shaking speeds of 350 to 400 rpm for baffled flasks, 400 to 450 rpm for regular flasks and tubes. All containers should be fixed on the platform, otherwise medium agitation will not increase with shaking speed. All high density growth media can reach OD600 = 30 to 50 at recommended shaking speeds with sufficient ventilation of the incubator and incubation room. At normal shaking speed of 250 rpm, high density growth media can reach up to OD600 = 10 which is still higher than commonly used media.

Aeration is directly related to the medium/container volume ratio. The lower the medium/container volume ratio, the better aeration. We recommend 1/4 medium/container volume ratio or less for shake flasks and 1/10 medium/tube volume ratio for round-bottom tubes. For example, 500 ml or less medium should be used for a 2 liter flask and 1.5 ml or less medium should be used for a 14 ml tube. higher medium/container volume ratios will result in lower cell densities. Conical tubes should not be used for bacterial cultures because of bad aeration.

Incubator and incubation room should also be sufficiently ventilated especially when 500 ml or more medium is used. Many incubators require temperature setting to turn on the ventilation fan. Room temperature incubation still needs temperature setting of 25 degree Celsius to turn the fan on.

Applications of high density growth media

Features of high density growth media

High density growth media support high density E.coli growth. In a shake flask under normal aeration conditions, common media such as LB can support E.coli growth up to a cell density of OD600 = 2 to 3. Richer media such as TB can grow E.coli to OD600 = 5 to 8. By contrast,  all of our proprietary high density bacterial growth media can grow E.coli to a cell density of OD600 = 30 to 50. This is over ten times higher than LB and over five times higher than TB. As a result, 5 to 10 times more plasmid DNA or protein can be produced in our high density growth media. Paired media DetoX^TM and InduX^TM can also reduce the toxicity of recombinant proteins. DetoX^TM medium contains a high level of inhibitors to inhibit the non-induced expression. When switched to InduX^TM medium, high levels of recombinant protein can be expressed. SecPro^TM medium can increase secretory expression 100 times over TB or SB.

In addition to supporting high density growth, our special media also contain trace metals, trace minerals, various vitamins, and unknown nutrients from animal serum. These chemicals will serve as prosthetic groups, co-factors or ligands for recombinant proteins. Therefore increased protein solubility, stability and activity are obtained from using these special media.

Time window to express protein is significantly extended in high density growth media. Protein expression is induced at early log phase which is OD600 = 5 to 10 for high density growth media. Protein expression may also be induced at OD600 = 20 to 30 if the recombinant protein is toxic to the host. In this case, the induction temperature may be lowered to 15 to 25 degree Celsius and shaking speed should be changed to 250 rpm. the time window to express protein can be as long as overnight or longer depending on the induction temperatures.

Plasmid and protein yields in these media are significantly higher than those that can be obtained from the general media. Our high density growth media are buffered chemically and metabolically. In addition to common buffers such as the phosphate buffer, our media are also buffered with balanced amount of sugars and organic buffers. Carefully balanced amounts of both sugars and organic buffers will maintain the pH of the culture in the E.coli growth pH units. For example, the pH of E.coli cultures of AutoX^TM media at OD600 20 is about 7. Close to neutral pH, antibiotics such as ampicillin will not be chemically degraded. As a result, over 90% of the cell population contains the plasmid. Both higher cell densities and higher proportions of the population containing the plasmid contribute 10 times or higher plasmid yield than LB. Recombinant proteins may also be induced at this cell density. A 10 to 20 times higher recombinant protein yield is also obtained from our special media than LB. In addition to casein peptone, yeast extract, sodium and potassium salts, and balanced buffer systems, our special media also contain vitamins, minerals, and trace metals. Some vitamins, minerals, and trace metals are needed for high density cell growth. Others are not needed by E.coli growth, but these additives and their metabolic products may serve as prosthetic groups, co-factors or ligands for recombinant proteins and therefore are critical to protein solubility, stability, and folding. In addition to higher yield resulting from using our high density growth media, many proteins are more soluble, stable, and functional when expressed in these media.

Benefits of high density growth media

Examples of using high density growth media

Related literatures of growth media

Growth media FAQs
Plasmid DNA yield
Protein yield
Protein solubility
Toxic protein cloning and expression

Related products of growth media

Bacterial E.coli growth media
DNA ladders or DNA markers
Expression vectors
Competent cells for cloning and expression
E.coli cell strains for protein expression

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