Introduction
Prokaryotic cell division is the type of cell division in which a single prokaryotic cell divides into two daughter cells. This process is essential for the survival and growth of prokaryotic organisms, including bacterial growth and archaea.
Prokaryotic cell division is a relatively simple process compared to eukaryotic cell division, which involves the formation of a mitotic spindle and the segregation of chromosomes. However, prokaryotic cells are able to divide much more rapidly than eukaryotic cells, allowing them to quickly colonize new environments and outcompete other organisms.
Additionally, prokaryotic cells also have other methods to increase their population, such as budding, fragmentation, and conjugation. These mechanisms allow them to adapt to different environments and to survive in conditions where binary fission is not possible.
Binary fission
Binary fission is the process of cell division by which a single cell divides into two daughter cells. It is a form of asexual reproduction that occurs primarily in prokaryotic organisms, such as bacteria and archaea
Stages of cell division
The process of prokaryotic cell division begins with DNA replication, in which the cell’s genetic material is duplicated.
Most bacteria only have a single circular chromosome. The place where replication starts on each circular chromosome is called the origin of replication, or just the origin. Replication ends at the terminus, which is right across from the origin. In a newly formed E. coli cell, the chromosome is packed and positioned so that the beginning and end are on opposite sides of the cell. Early in the cell cycle, the origin and terminus move to the middle of the cell, and at the origin, proteins that are needed for chromosome replication get together.
The part of the cell that makes new DNA is called the replisome, and DNA replication goes both forward and backward from the origin. As the progeny chromosome is made, the two origins move to opposite ends of the cell, and the rest of each chromosome follows in an orderly way.
During the next stage, called cytokinetics, the cell’s cytoskeleton and cell membrane begin to reorganize. A ring-like structure called the divisome forms around the equator of the cell, and this structure helps to separate the cell into two daughter cells. The divisome consists of several proteins, including FtsZ, FtsA, and FtsE, which work together to form a contractile ring that constricts the cell and pinches it in half.
Once the cell has been divided into two daughter cells, the process of cytokinesis is complete. The two new cells then begin to grow and mature, and the process of binary fission can begin again.
Cell division in archaea
Stanieria is a cyanobacterium, which means that, like plants, it can make its own food. This bacteria starts with a cell called a baeocyte, which is a very simple cell. This cell keeps making copies of DNA, which fills the cell with it. When there are enough copies of the DNA, the cytoplasm divides quickly, giving each piece of DNA a place to live that is full of cytoplasm. Then, the new cells burst out of the baeocyte, making up hundreds of new baeocytes.
Fragmentation
Fragmentation is a type of multiple cell division in prokaryotes that refers to the process by which a single cell breaks apart into multiple smaller cells, which can then grow and divide independently. This process can occur naturally or can be induced by environmental factors such as high osmotic pressure or exposure to certain chemicals.
The process of fragmentation begins with the weakening of the cell wall and the cell membrane. This can be caused by various factors, such as changes in osmotic pressure, exposure to antibiotics, or the presence of enzymes that degrade the cell wall. Once the cell wall and membrane are weakened, the cell begins to break apart, resulting in multiple smaller cells.
One example of fragmentation in prokaryotes is seen in the bacterium Streptococcus pneumoniae. This bacterium can undergo fragmentation in response to changes in osmotic pressure, resulting in the formation of smaller cells called tetrads. These tetrads are able to survive in environments with high osmotic pressure, such as the human respiratory tract, where they can cause infections.
Another example is seen in Myxococcus Xanthus, a soil-dwelling bacteria, that can form multicellular structures called fruiting bodies, through a process called developmental cell death, where cells at the center of the structure die, and the rest of the cells divide and form spores.
Fragmentation can be a useful survival strategy for prokaryotic cells in adverse conditions, as it allows for the formation of smaller cells that can survive in environments where larger cells would not. Additionally, fragmentation can also increase the chances of survival by increasing the population size and allowing for the colonization of new environments.
Conjugation
Conjugation is a type of sexual reproduction that occurs in prokaryotic organisms, particularly in bacteria. It is a process by which genetic material is transferred from one cell to another through direct cell-to-cell contact. This process allows for the exchange of genetic information between cells, leading to the formation of new genetic combinations and the evolution of new strains of bacteria.
The process of conjugation begins with the formation of a specialized structure called a pilus, which is a thin, hairlike appendage that extends from the surface of one cell (the donor cell) and makes contact with the surface of another cell (the recipient cell). Once contact is established, the pilus retracts, pulling the two cells together.
Once the two cells are in close proximity, a tube-like structure called a conjugation pilus or sex pilus is formed, which allows for the transfer of genetic material from the donor cell to the recipient cell. The genetic material that is transferred is typically a plasmid, a small, circular piece of DNA that contains genes that confer resistance to certain antibiotics or other beneficial traits.
Stages of conjugation
The process can be divided into three stages:
1- Pilus formation: The donor cell initiates the process by extending a pilus towards a recipient cell.
2- DNA transfer: The pilus brings the two cells together, and a sex pilus is formed. Through this pilus, the plasmid DNA is transferred from the donor to the recipient cell, this transfer can be unidirectional or bidirectional.
3- Pilus retraction: After the transfer of DNA is complete, the pilus is retracted and the two cells separate.
Conjugation allows for the exchange of genetic information between cells and the formation of new genetic combinations. This process can lead to the evolution of new strains of bacteria, which can be beneficial or harmful, depending on the context. For example, the transfer of antibiotic resistance plasmids between bacteria can contribute to the emergence of antibiotic-resistant strains of bacteria, which can be a public health concern. However, conjugation can also be used to transfer beneficial traits, such as the ability to degrade pollutants, to bacteria that are used in bioremediation.
Conclusion
Prokaryotic cell division is the process by which a single prokaryotic cell divides into two daughter cells through binary fission. This process is essential for the survival and growth of prokaryotic organisms and allows them to quickly colonize new environments. Additionally, prokaryotic cells have other methods to increase their population, such as budding, fragmentation, and conjugation.
References
Tortora, G. J., Funke, B. R., & Case, C. L. (2021). Microbiology: An introduction. Pearson Education Limited.
Willey, J. M., Sandman, K. M., Wood, D. H., & Prescott, L. M. (2019). Prescott’s microbiology (11th ed.). McGraw Hill.
