Microbial growth curve

The increase in cell mass and size that occurs as an organism develops is referred to as growth. Each organism has its own unique characteristics. For energy production and cellular biosynthesis, the organism requires a specific set of basic parameters. The development of an organism is influenced by nutritional and physical factors. Physical factors such as the medium in which the organism is expanding must be considered.

Microbial Growth Curve (Key Takeaways)

• A bacterial population’s number of live cells grows with time, and the growth curve is separated into four stages: lag, exponential (log), stationary, and death.
• The first stage is the lag phase, which occurs when bacteria are not dividing but are metabolically active.
• The exponential also referred to as the log phase, is characterized by rapid growth.
• In the stationary phase, growth comes to a standstill when the number of dying cells equals the number of dividing cells.
• During the death phase, the number of living cells decreases exponentially.

 The bacteria’s viable cells should be seeded onto sterilized broth and incubated under an appropriate growth curve in microbiology to examine the bacterial population growth. 

Bacteria are unicellular organisms with only one cell. The bacterium consumes the parts of the medium and expands in mass and size. The bacterium is said to be actively growing in Microbiology when this happens in the microbial growth curve.

Researchers can study the growth of bacterial dynamics by plotting the log of cell number versus time or cell growth versus incubation time. A sigmoid curve, or standard growth curve, results in this process.

The increase in the organism’s cell mass and the microbial growth curve are measured with a Spectrophotometer.

Lag phase

It takes some time for a microorganism to adapt to the new conditions when it is first put into a new medium. When cellular metabolism speeds up and cells expand, bacteria are unable to replicate which results in a decrease in the mass of a cell.

The period of the lag phase is related to the organism’s preceding state of growth. It takes a microbe longer to acclimate to its new surroundings when it is introduced into a nutritionally poor medium.

As the organism begins to transduce the proteins, the lag phase lengthens.

When an organism is transferred from a nutritionally deficient medium to a nutritionally rich medium without delay and thus has a shorter lag phase in the microbial growth curve.

Exponential phase

During this phase, microorganisms multiply and divide rapidly. Their metabolic activity increases and binary fission DNA replication begins in earnest.

Generation time is the amount of time it takes bacteria to double in size over a particular length of time. The period of time it takes for an organism to reproduce varies.

Stationary phase

As the bacterial population develops along the microbial growth curve, it consumes all of the nutrients in the growth medium. In the medium, toxic metabolites, waste materials, and inhibitory compounds such as antibiotics accumulate.

This alters the circumstances of the medium, such as temperature and pH, making bacterial growth more difficult. The rate of reproduction of the bacteria reduces until the number of cells undergoing division equals the number of cells dying, at that point of the time the bacterium stops dividing completely.

The growth rate remains constant because the cell count is not increased. When a stationary cell is shifted to a new medium, it can quickly switch to the exponential phase and restart metabolic processes.

Death phase

The bacterium’s capacity to move to the Death phase is aided by the loss of nutrients and consequent accumulation of metabolic waste products and other toxic compounds in the media. 

During this time, the bacterium’s capability to reproduce is completely lost. Bacteria typically start to die when they are exposed to conditions that are unfavorable, and death occurs quickly and uniformly.

 The total number of dead cells outnumbers the number of living cells. When some organisms are resistant to this condition, endospores allow them to survive in the environment.

Growth and Oxygen in Bacteria

Bacteria are divided into groups based on their oxygen requirements and tolerance levels. Obligate aerobes are bacteria that cannot thrive without oxygen. Because they convert oxygen to energy during cellular respiration, these microorganisms rely on oxygen for living.

Other bacteria, in contrast to those that can, cannot survive in the presence of oxygen. When exposed to oxygen, obligate anaerobes stop producing energy, affecting the microbial growth curve. 

Other bacteria are facultative anaerobes, which means they can survive with or without oxygen. When there is no oxygen available, they generate energy by fermenting or respiring anaerobically.

Aerotolerant anaerobes are anaerobes that breathe anaerobically without being affected by oxygen. Microaerophilic bacteria require oxygen to survive, but they can only flourish in low-oxygen environments. 

Campylobacter jejuni is a microaerophilic bacterium that lives in the digestive tract of animals and is one of the most common causes of human foodborne illness.

The Effects of Light on Bacterial Growth

For some bacteria to grow, they require light. The light-capturing pigments are present in these microbes that allow them to collect and convert light energy at specific wavelengths.

Cyanobacteria are photoautotrophs or photosynthesis-dependent organisms. These microbes possess the pigment chlorophyll, which enables them to absorb light and produce oxygen through photosynthesis.

Deep aquatic zones are full of purple and green bacteria. Purple and green bacteria, for example, do not produce oxygen and instead photosynthesis using sulphur.or sulphide

These bacteria contain bacteriochlorophyll, a pigment that absorbs light at shorter wavelengths than chlorophyll.

Conclusion

Bacteria require specific conditions to grow, which are not the same for all bacteria. Many factors influence the growth curve in microbiology. Additional factors to take into account include atmospheric pressure, osmotic pressure, and moisture availability. The time it takes for a bacterial population to double, also known as generation time, varies by species and is governed by how effectively the species’ development requirements are met. We hope you now understand how to describe a microbial growth curve.