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.
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.
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