The chief one here is that – given that all cells in the culture are genetically homogeneous and see the same ‘environment’, and There should be nothing controversial in the above passage, but in fact it hides a variety of assumptions that themselves conceal a considerable feast of very interesting physiology.
PANOPLY 14660 SERIAL
The same is true for cultures undergoing serial transfer (where there is slightly more of a focus on selection for genotypic variants that grow faster – see e.g. Our interest here is largely in cells that have not mutated.ġ1) cultures was and is entirely consistent with this view of steady-state microbial doubling via homogeneous cell cycles that are common, within statistical fluctuations, to each cell. Some authors recognise an extended “period of prolonged decrease”Ĩ52 during which some of the survivors undergo significant dynamics, and in which mutants are selected. A typical laboratory bacterial culture.Īfter the end of stationary phase the viable count decreases over time, but very rarely to precisely zero. Inoculation of a new broth culture with a similar number of viable cells from this culture usually provides a simple repeat of the previous cultureĦ, and in the absence of mutation may reasonably be anticipated, for organisms proliferating asexually, to be played out indefinitely. Again, after a further period, the viable or colony count decreases (often to quite low levels if such starvation is carried out for extended periods).
In time this increase in cell numbers ceases, usually because of the exhaustion of a nutrient in a closed system, or sometimes in part or whole because of the build-up of toxins. Population distribution of organisms in different parts of their cell cycle during the exponential phase is thereby unchanged and thus in a steady state (from which the cell cycle parameters can even be inferredĥ). Apart from the changes in nutrient concentration, and for non-synchronised cultures, it is generally taken that cells pass smoothly through their cell cyclesĮn route to doubling their numbers by binary fission. After a lag phase the number of culturable cells (the ‘viable count’Ĥ, as judged by plate counts of the number of colony-forming units observable on the same medium solidified by agar or a similar material) is observed to increase, typically exponentially, for a number of generations (the growth phase or exponential phase). We seed a suitable growth medium with an appropriate inoculum of cells known to be capable of replicating in that growth medium. “Bacterial populations in both batch and continuous culture are much more heterogeneous than is normally assumed, and such cultures may consist of several types of subpopulations simultaneously differing in viability, activity and integrity of the cells”Ĭonsider a typical axenic flask or broth culture of bacteria (įigure 1), arguably the staple of modern laboratory microbiology. “It is now well established that some micro-organisms can, under certain conditions, be deprived of all visible signs of life and yet these organisms are not dead, for, when their original conditions are restored, they can return to normal life and activity”
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