Bacteria, known as prokaryotes, are microscopic single-celled organisms. They are found in abundance in every type of climate and environment on Earth as well as the intestines, mouths, skin, feathers, fur, or scales of other living organisms. Some are pathogenic and will cause illness while most others are harmless or serve an important purpose with symbiotic relationships to other organisms. Bacteria are typically found in large groups known as colonies. These colonies are made up of millions of bacterial cells. How do bacteria become so numerous? The key to their numbers lies in their methods of reproduction.
Because bacteria are only made up of a single cell, their methods of reproduction must be fairly simple and straight forward. Unlike higher multi-celled organisms that reproduce using much more complex methods that can take large amounts of time, bacteria have the advantage of creating new bacterial cells in a matter of hours, or in some cases, in a matter of 15-20 minutes.
The main method of reproduction in bacteria is known as binary fission. Binary fission is a method of asexual reproduction as the cells are basically making clonal copies. This method is accomplished when the genetic material inside the mother cell divides into two copies and then moves to opposite ends of the cell. The cell elongates and then forms a double wall at the center. It is at this point that the cell splits off into two resulting daughter cells, both of which are genetically identical to each other. When the cells have fully matured, they may also begin the process of binary fission. It is through this method that bacterial colonies are formed of millions of identical bacterial cells.
While binary fission is the most efficient way of reproduction for bacteria to quickly increase their numbers, there are drawbacks to this method. Because binary fission is basically asexual reproduction resulting in only clones, the clones are more susceptible to threats that can wipe out the entire colony. A solution to this problem is to employ some sort of way to become genetically diverse.
Conjugation is a method of transferring genes from one bacteria to another. In a way, it can be compared as method of sexual reproduction as it not only results in genetic diversity but also requires the cells to join together to make the transfer successful. For conjugation to take place, two cells are joined temporarily with one cell being the donor and the other the recipient. The walls of the cells are joined by a temporary structure, known as the sex pilus, which also serves as the gateway for the gene transfer from the donor cell to the recipient cell. The recipient cell will now possess genes from the donor and can produce daughter cells that are genetically different from itself.
Conjugation does not occur in all bacterial cells. In order for it to be successful, there needs to be two distinct strains present within the bacteria colony. Donor cells are known to possess the fertility factor, or be designated as F+, while the recipient cells are known as F- as they lack the fertility factor. Without the two distinct strains, conjugation does not occur.
Other methods that allow bacteria to acquire different genetic material are through the processes known as transformation and transduction. These methods are not types of reproduction but rather a way to keep a colony of bacteria genetically diverse.
Transformation is when a bacterial cell actually picks up genetic material from its environment. In most cases, bacterial cells of one strain have died, leaving their DNA available to be used by a different strain of the same species. Not all types of bacteria can do this as it takes specific enzymes to actually take, cut, and insert the DNA from one cell and place it into the chromosome of another. The resulting bacterial cell would then have traits of both itself and the dead bacteria in its newly fashioned chromosome that could then be subsequently copied and passed down to its daughter cells.
Transduction is when a bacterial cell acquires genetic material from another bacterial cell through a virus known as a bacteriophage. When bacteriophage infect bacterial cells, they integrate their own viral DNA into that of the bacterial cell which creates the replication of the viral particles. In some cases, the bacteriophage does not kill the cell and the bacterial cell is left with not only the viral DNA but with the DNA of the last bacterial cell that the bacteriophage used as its previous host.
Understanding the methods of bacterial reproduction is the backbone for a host of breakthrough research in the fields of genetics and biotechnology. Bacterial gene transformation and transduction have paved the way for the creation of transgenic organisms as well as the invention of gene therapies in the effort to combat many genetic disorders and diseases. The research and discoveries yielded from these microscopic single-celled organisms has created huge scientific contributions that have benefited more than just human life, but also a greater understanding of the basic functions of reproduction.