There are three ways by which the reproduction of bacteria occurs; those processes are (1) Vegetative, (2) Asexual and (3) Sexual. Let us go on a discussion:
1. Vegetative Reproduction of Bacteria:
The vegetative reproduction of bacteria may be divided into two process : The Binary fission process and Budding process.
Binary Fission :
The most common way by which the bacteria reproduce itself is the Binary Process. It is a process by which a single bacterial cell simply divides into two in half an hour time. The various events of Binary fission are as follows :
[i] The nucleoid gradually become elongated in size and form dumbel-shaped structure.
[ii] They still remain attached to the plasma membrane with the help of mesosome.
[iii] The duplication of DNA and mesosome takes place and they separate from each other.
[iv] The daughter mesosomes and nucleoids migrate towards the opposite poles.
[v] The plasma membrane invaginates at the center and the parent cell is divided into two identical cells
It is a comparatively rare process of reproduction of bacteria observed in few like Rhodopseudomonas.It is a process by which the vegetative cell forms a lateral protuburance in the form of an outer bulge containing a fragment of genetic material or nucleoid in it. The bud may either get separated from the parent cell or may form a colony along with the parent cell.
2. Asexual reproduction of Bacteria:
This type of reproduction of bacteria is occurred in general by the formation of endospore.
Formation of Endospore: The production of endospore is not always considered to be a means of asexual reproduction, but rather it is a mechanism of perennation, when the bacterial cell survives during an unfavourable condition. The thick walled oval or spherical structure that encloses the bacterial protoplast during unfavourable condition is known as endospore.
During the formation of an endospore, the cell remains intact, but the bacterial protoplast shrinks to the center or in the sub-terminal area of the cell and gets enclosed within a three layered wall called cndosporium. It is followed by another two layered wall and the cell membrane and protoplast have shrunk to the extreme center. The area between the endosporium and the original cell wall remains empty and is called exosporium. With the initiation of water, that is favourable condition, the wall is ruptured and the bacterial cell emerges out. The endospore formation is observed in common bacterial species like Clostri Bacillus.
3. Sexual Reproduction of Bacteria:
The process of sexual reproduction of bacteria normally takes place when the condition is unfavourable, when adequate substrate and water are not available in the environment and they are of the following types :
This is a physiological process by which the genetic mater transferred from one individual bacteria to the other during sexual reproduction.In case of bacteria, there is no sexual dimorphism. They are recognized as F+male or donor strain and F- or female or recipient strain. The F factor is also calk fertility factor or sex factor and is represented by an extra nuclear circular DNA present only in male. But as it is lacking in female, they are called F- strain.
Events of conjugation:
The major events during the process of conjugation are as follows :
[i] Two seperate bacterial cells belonging to opposite strains come close to each other.
[ii] The conjugation bridge is formed between the two cells using the sex pili or F-pili.
[iii] The F factor replicates in the male.
[iv] The F factor slowly migrates into the female through the conjugation tube and an incomplete zygote or merozygote is formed.
[v] The presence of F factor in female transforms the F- strain to F+ strain.
[vi] The product of conjugation is just the genetic recombination product of the two strains of cells. The progenies developing from this recombinant product conserve this character of the recombinant DNA that has been transferred during conjugation.
It is a physiological phenomenon by which the incorporation of DNA from one bacterium into another results in the development of a new genotype. This is also due to genetic recombination. During transformation the cells which are ready to take up naked DNA and get transformed are said to be competent cells.
This process of sexual reproduction of bacteria was first observed by Zin and Lederberg (1952). It is the process of transfer of'DNA fragmentfrom one bacteria into the other with the help of a bacteriophage. The process also results in genetic recombination.