Tuesday, October 25, 2011

Shifting bacterial population distribution curve to the right or left

As per my model, a bacterial population in a colony is heterogeneous with respect to growth rate and age. There are small subpopulations of both young and senescent bacterial population in addition to the major population which have an intermediate growth rate. The growth rate of the whole population will be close to the intermediate population as they comprise the major population.

However, the bacterial population distribution curve can be shifted either towards the left or the right. It can be shifted towards the left by growing the bacterial culture in early exponential phase. In this case, the growth rate of the culture gradually increases as more young bacteria are selected (as described in the previous blog on Sep.19). However, this increased growth rate of the culture may not be a permanent feature since the bacteria undergo senescence. Thus, if the culture of young bacteria is allowed to grow and reach stationary phase, the growth rate may gradually decrease due to the gradual increase in senescent population. If 50 ul of this stationary phase culture is transferred to 3 ml of fresh medium and allowed to grow, the growth rate may further reduce. If this process is repeated, the growth rate may reach the initial rate.

On the other hand, the bacterial distribution curve can be shifted to right by incubating the bacterial culture with aminoglycosides which results in the selection of slow dividing senescent bacteria (see the blogpost on Oct.5). Whether they can be shifted back to normal depends upon the stage of senescence. Bacteria towards the terminal stage of senescence can not be reverted back and in this case it may not be possible to shift the growth rate to normal.

Next- My model of bacterial senescence.

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