Bacterial Growth Curve
The bacterial growth is measured by the increase in population, either by measuring the increase in cell number or the increase in overall mass and not in terms of increase in size.
Bacteria or prokaryotes are known to reproduce asexually like binary fission while the Eukaryotes can divide both through asexual and sexual methods like multiple fission, budding, and the production of spores.
- Since bacteria in the lab are quick to grow, their development has been extensively studied.
- It has been determined that bacteria can evolve in a consistent fashion in a closed system or batch culture (no food added, no waste removed), resulting in a growth curve.
- It consisted of four different growth phases: the lag period, the exponential or log period, the stationary phase, and the decline phase
- The lag phase is a time of adaptation, where the bacteria adapt to their new environments.
- The lag phase is determined by cellular activity but not growth.
- Depending on how different the environments are from the environments from which the bacteria originated, as well as the state of the bacterial cells themselves, the duration of this stage varies.
- A community of cells is put in a medium rich in nutrients and is allowed to synthesize.
- Cells synthesize RNA, enzymes, and essential metabolites which are not present in their new environment in this stage.
- The repair of macromolecular damage sustained during the stationary phase and the synthesis of cellular components required for growth may be included in this step.
- The cells adapt accordingly to the availability of temperature, pH, or oxygen.
- The cells are shown to grow in number, but there is no division of cells.
- The period of the lag process is determined not only by the species of bacteria but also by the amount of time the cells stay in starving conditions.
EXPONENTIAL OR LOG PHASE
- Cell doubling characterizes the exponential process.
- The number of new bacteria that occur per unit of time is equal to the population at present.
- In order to synthesize required macromolecules, the physiology of exponential bacterial growth and replication requires several rounds of DNA synthesis, coupled with transcription and translation. A number of gene regulation mechanisms regulate these critical activities.
- If expansion is not regulated, the doubling will occur at a constant rate, such that for each successive cycle, both the number of cells and the population rate will double.
- Cells in this phase are the healthiest and most uniform.
- A straight line is generated by plotting the natural cell number logarithm against time. The real growth rate of the organism, which is a measure of the number of divisions per cell per unit time, is the slope of this axis.
- The exact rate of this development depends on the growth factors influencing the number of events of cell division and the possibility of survival of all daughter cells. However, since the medium is quickly drained of nutrients and enriched with waste, exponential growth can not occur forever.
- When the bacterial population ran out of essential nutrients such as depletion of a nutrient and/or the formation of inhibitory products such as organic acids, it went to the stationary phase.
- It is characterized by an equilibrium between the numbers of cells that divide and die and represents a plateau in the growth curve.
- It results in a flattening of the growth curve.
- In the stationary phase, cultures accumulate toxic catabolism products in the atmosphere, leading to a decrease in the number of viable cells, known as the death phase.
DEATH OR DECLINE PHASE
- The number of dying cells begins to grow as nutrients become less available and waste materials increase.
- At the death phase, bacteria run out of nutrients and die. The steepness of the slope relates to how quickly cells are losing viability.
- They pour their contents into the air when dying cells lyse or split open, making these nutrients visible to other bacteria.
- As a means to assess cell density, the turbidity of culture is being measured.