Bacteria are microscopic single-celled organisms that have all of their genetic information contained in one loop of DNA.
They come in a variety of shapes and can be found in virtually every environment on Earth, including soil, water, and the bodies of animals and humans. In fact, there are around 10 times more bacterial cells in the human body than there are human cells.
But how do these simple organisms reproduce? How can there be so many bacterial cells? Let’s take an in-depth look at the reproduction of bacteria.
Bacteria may be simple, single-celled organisms but they have the capacity to reproduce in great abundance. This prolific reproduction is only possible under the right conditions but can occur in one of two ways, either sexually or asexually.
First, we will look at the different forms of asexual reproduction that a bacterial cell can undergo.
This form of reproduction is very common amongst single-celled organisms and bacteria are no different. It involves the single parent cell dividing into two other cells, called daughter cells.
The daughter cells are perfect replicas of the parent cell. For binary fission to happen and be successful, the bacterial cells need to grow to the appropriate and fixed-size first.
Once this size is achieved, each individual cell replicates the genetic material and forms two DNA molecules. These molecules then attach to the cell membrane in separate locations.
Once the molecules are attached, the cell membrane begins to expand and grows inwards, forming the daughter cells that each have a DNA molecule.
This process can be remarkably fast as in ideal conditions, it can be achieved in only ten minutes.
This second form of asexual reproduction is also known as fragmentation. It occurs when the mother cell forms a bud at one end.
The mother cell also makes a nucleus for the bud through the process of mitosis, which involves the replication of chromosomes and segregating the new chromosomes into a new nucleus.
The bud then grows until it is the same size as the mother cell and separates. After the separation, it becomes a distinct and different organism.
Although the nucleus is formed through mitosis and by replicating chromosomes, it is possible for the offspring bacteria to be different from the mother cell.
In bacteria, this form of reproduction is much rarer than asexual reproduction is. However, it does still occur and is an important process for bacteria.
As asexual reproduction results in daughter cells having the same genetic material as mother cells, they will be affected by the same types of antibiotics.
For bacteria to evolve and have variations in their genetic material, sexual reproduction is essential.
By reproducing sexually, bacteria can develop resistance to particular antibiotics and adapt to whatever changes happen to their environment. Let’s look at the different types of sexual reproduction that bacteria can undergo.
In this form of sexual reproduction, DNA is transferred from one bacteria cell to another. The donor cell transfers this information through a pilus, which connects to the recipient cell.
Usually, the DNA is transferred in the form of a plasmid. The reason why some donor cells become donors is because they have a special chunk of DNA which is known as the “fertility factor.”
This F factor contains all of the DNA codes needed to form the pilus. The donor cell also has a special site that allows the DNA transfer to happen.
Once the donor has given the DNA to the recipient, the recipient cell now has this F factor too and will be able to create its own pilus to transfer DNA.
In this case, a bacterial cell collects and takes in DNA that has been disposed of or shed by other bacteria. Often, this DNA is the remnants of dead bacterial cells that are still in the environment.
The DNA can be in the form of a plasmid and it attaches to living bacterial cells before being absorbed through the cell membrane and incorporated into the DNA of the living cell. This process can have great effects on the receiving cell.
For example, if the living bacterial cell is harmless but receives and incorporates DNA that includes a toxin gene, it can become pathogenic in its own right.
Transduction is a different beast from the other types of sexual reproduction. Whereas both conjugation and transformation involved different bacterial cells coming into contact to exchange DNA, transduction involves bacteriophages.
These are viruses that infect bacteria and take them over in order to make even more bacteriophages.
Transduction occurs when a bacteriophage attaches itself to a bacteria cell and inserts some of its own viral DNA into the cell.
The rogue bacteriophage material then gets replicated inside the bacterial cell and released, where it can then attach to any other bacterial cell in its own right. This results in bacteriophages infecting even more bacterial cells.
What Affects The Reproduction Of Bacteria?
We spoke earlier about the rate of bacterial reproduction and how it needs the ideal conditions to occur at maximum speed. In binary fission, a parent cell divides into two daughter cells, leading to an exponential growth pattern.
Each division cycle, or generation, doubles in size, so the first generation may be only two cells, but the second generation will be four cells.
This keeps happening, leading to generations of 8 cells, 16 cells, 32 cells, 64 cells, and so on. As you can see, the number of bacteria cells can quickly get out of hand.
However, this rapid exponential growth can be slowed down by a number of factors. These include the following factors.
- Nutrition Concentration – bacterial growth occurs faster when the environment has a higher concentration of nutrients that promote growth. Different bacteria need different nutrients
- Temperature – each bacteria has a minimum and maximum temperature for growth. If the temperature becomes either too low or too high, growth will not occur.
- pH – different bacteria need different pH levels. Most bacteria thrive in neutral conditions but there are some that require acidic environments
- Salt And Ions – metal ions are required by bacteria to produce enzymes and proteins. Most bacteria do not need salt but will not be negatively affected by low concentrations of it. A few types of bacteria need high salt levels.
- Gaseous Requirements – both oxygen and carbon dioxide are important for bacterial growth and reproduction. For some bacteria, either or both are essential
- Water – this has the biggest influence on bacterial growth
Bacteria can reproduce either asexual or sexually. Asexual reproduction such as budding and binary fission are more common, with binary fission being the most common form of reproduction overall.
However, sexual reproduction can also occur and is an important method for bacterial evolution and change despite its rarity. Sexual reproduction can take the form of conjugation, transformation, or transduction.
Bacterial reproduction can occur very rapidly. The combination of prolific reproduction and random mutations ensures that bacteria evolve very quickly, often leaving scientists playing catch up when it comes to developing antibiotics.
Bacteria are also very quick to adapt to environmental changes, making them hardy and difficult to combat.
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