How to determine concentration of cells at stationary phase?
Answers
Explanation:
In most labs, the use of overnight cultures is standard fare.
The scheme is that an inoculum of several thousand cells is pipetted into a 5 mL tube and then grown overnight.
During those 8-12 hours, the transparent and vacant media transforms into a saturated culture as shown in
with a characteristic density of cells measured via the optical density at 600 nm (OD600) with a value of ≈2.
With a calibration curve or using the collection of characteristic conversion factors shown in Table 1, one can transform the OD value into a cell count of 109 cells/mL (BNID 104831). Under these conditions, the cells occupy about 0.1% of the total medium volume
. The mean spacing between the cells is roughly 10 microns, a high density but still not nearly as high as the cell densities in environments such as the guts of animals, which are typically a factor of ten higher (BNID 104951, 104952, 104948, 102396).
Examples of the extreme crowding in such environments are shown in , illustrating the crowded cellular environment in the termite gut, and showing a trophosome – an organ in deep-sea tube worms packed with bacterial symbionts supplying its energy from sulfur oxidation in a biological process completely independent of the sun’s energy.
In fact, many biologists make use of such dense environments on a daily basis by growing colonies of bacteria on agar plates. Even in the sediments of the ocean floor the bacterial densities are sometimes as high.
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