Bacterial Growth and Growth curve notes

Introduction: Bacterial Growth

Growth in bacteria is defined as the increase in cell number rather than cell size. It depends upon the ability of cells to form New Protoplasm from nutrients available in the environment.

The increase in bacterial cell number occurs by cell division which is known as binary fission.

• Binary fission begins with the replication of bacterial DNA.

• DNA divides- transverse septum formed by a cell wall and membrane.

• the plasma membrane then grows inwards and split the cell into two daughter cells through a process called cytokinesis.

• FtsZ proteins play an important role in cell division, it is homologous to tubulin.

• The cellular concentration of FtsZ protein regulates the frequency of division.

When a bacterial cell is inoculated into a flask containing culture medium incubated, it enters into a rapid growth page during which bacterial cells divide and increases their population. Since the bacteria are not transferred to a new medium, the increasing population of bacterial cells, after sometime inter a stationary phase. Eventually, the stationary phase of the bacterial population culminates into a death phage. (A batch culture can be considered to be a closed system).

Growth in batch culture can be divided into four distinct phases- these are lag phase, Log Phase, stationary phase, and death phase.

Lag phase

during the lag phage, there is no increase in number. It is a period of adaptation of cells to a new environment. There is no change in number but an increase in mass.

Log Phase

In this phase, the bacterial cells increase their number exponentially with time [(2)0, (2)1, (2)2, (2)3, until after n divisions, (2)n]. The cell divide at a constant rate depending upon the composition of the growth medium. The rate of exponential growth of a bacterial culture is expressed as generation time, also the doubling time of the bacterial population. The time interval required for the same to divide is called generation time.

Stationary phase

Exponential growth cannot be continued forever in batch culture (closed system). In this phage, the cell growth rate has leveled off and become constant. The number of cells that proliferate equals the number of cells that die. Population growth is limited by one of three reasons:

1. The available nutrients have been depleted.

2. Accumulation of inhibitory metabolite or end products.

3. Exhaustion of space, in this case, is called a lack of biological space.

Death phase

If incubation continues after the population reaches the stationary phase, a death phase follows, in with the viable cell population decline.

Calculation of Generation time: