Introduction
Objective
- To identify changes in a bacterial population in each of the four stages of a growth curve.
- To determine turbidity.
- To estimate the generation time.
- To determine the actual growth rate of a bacterial culture by constructing a growth curve.
Materials and Methods
For this experiment, the nutrient broth culture (12-18 hours) used is E. coli DH5α.
The medium includes the following materials:
- Beef extract – 3.00;
- Peptic digest of animal tissue – 5.00;
- Nutrient broth ingredients – gl-1;
- Final pH (at 25°C) 6.9 ± 0.2.
The components mentioned above were dissolved in the required amount of distilled water for the experiment. The method of sterilization of the elements was the autoclave.
The materials used for the preparation of the lab report are the following:
- Orbital incubator shaker,
- 15 ml test tubes;
- 250 ml conical flasks;
- 1.0 and 0.2 ml sterile disposable tips;
- Laminar hood;
- Micropipettes;
- Glassware marker.
Discussion
Since the log phase is when microbial cell division happens quickly, it must be used to estimate bacterial growth. As bacterial cell division continues throughout this phase until it reaches the stationary phase, researchers can see each bacterium’s population rise significantly. Consequently, it would be perfect for assessing bacterial growth using the log phase of a growth curve.
The Lag, Stationary, and Death phases are the remaining phases of the growth curve (General microbiology laboratory manual, 2022). The Lag phase, which occurs when a new group of bacteria is transferred to a different growth medium so it can have time to synthesize the new nutrient source and ingredients and adapt to the environment, is the first stage for all bacterial cells (General microbiology laboratory manual, 2022). Each microbial cell will evolve once adaptation has taken place, ingesting nutrients until it is prepared for division.
The third stage, known as the stationary phase, is characterized by the bacterial cells using up all the nutrients that can be used for growth. In this stage, the rate at which bacterial cells divide decreases or stops, and population increase interrupts (General microbiology laboratory manual, 2022). The examined bacteria’s generation time is typically influenced by temperature. Although the bacterial domain does not outperform the archaeal domain in terms of severe survival, it is known to survive in various environmental conditions with minor damage from constant change (General microbiology laboratory manual, 2022).
Despite this, each microbe does have a specific ideal temperature range in which it can grow or thrive. The growth curve and data analysis indicate that 37 °C is the perfect growth temperature for Escherichia coli. Like other bacteria, Bacillus subtilis has a 37 °C optimal development temperature that corresponds to the environmental conditions of its natural habitat, including soil (General microbiology laboratory manual, 2022). Additionally, the two species grow differently from one another. As the growth curve shows, E. coli multiplies or develops more rapidly and increases its population at 37 °C than B. subtilis, which is reasonable.
In contrast to B. subtilis, E. coli multiplies quickly in the adult human digestive tract, which shares a symbiotic connection with the host. This bacterium is found in environments like soil, where nutritional availability and environmental factors like temperature are constantly changing (General microbiology laboratory manual, 2022). As a result, it may not require 37 °C to survive as much as E. coli. Determining B. subtilis’ actual optimum temperature in situ would be challenging.
Conclusion
This experiment aims to evaluate bacterial growth by tracking changes in cell count. By monitoring variations in the turbidity, or cloudiness, of the solution, changes in cell number can be estimated. Light will be scattered by particles in a solution proportional to their overall amount.
The turbidity of the solution would also grow as the quantity of bacteria increases. Using a spectrophotometer allows for determining the turbidity of a solution during the experiment. Turbidity is not a viability indicator, which means that a rise in turbidity indicates that there are additional cells in the solution, but it does not indicate the proportion of living vs. dead cells.
Reference
General microbiology laboratory manual. (2022). Department of Biological Sciences at Old Dominion University.