Population distribution of an E. coli colony- comparison with Stewart et al. (2005) model

As per Stewart et al. (2005) (discussed in the last blog), the daughter cell formed from a mother cell is a rejuvenated offspring with full reproductive potential. So, if we designate x for virgin cells, x+1 for cells that have undergone 1 division, x+2 for those undergone 2 divisions and so on, then approximately 50% of a normally dividing  population in a colony of bacteria will be virgin cells (x), 25% will be x+1, 12.5% will be x+2 and so on. Hence if we plot the percentage of different populations on a graph, a half-bell curve distribution will be obtained. However, it may not be as perfect as one below as the growth rate of all cells are not the same (mother cells have reduced growth rate as it undergoes senescence).

However, my model of E. coli senescence is closer to that of S. pombe senescence (discussed on September 6 blogpost). In this model, the old cells do not give rise to rejuvenated offspring, but generate old cells itself. However, majority of the cells are relatively young cells with limited damaged or carbonylated proteins and this pool of young cells are large enough to prevent the extinction of the population. Another important feature in my model is the presence of a small population of virgin cells with no damaged or carbonylated proteins. Thus a major difference between Stewart et al. (2005) model and my model is that in the former, majority of the population are virgin cells (rejuvenated offspring) whereas in the latter, majority of the population are young bacteria with limited carbonylated proteins, along with a small population of virgin cells.

Thus, the population distribution in my model follows a normal distribution curve. However, it may not be a perfect bell shaped curve but can be skewed in favor of young cells. A bell-shaped curve indicates that there are small populations of fast-dividing young bacterial cells as well as slow-dividing senescent cells in any bacterial colony.

Is it possible to isolate any of these small populations? The answer is yes – both young cells and old cells can be isolated. In the next few sections, I will discus how to isolate these two populations separately.

Next- Isolation of fast dividing, hypervirulent, young bacteria