Reproduction in Bacteria: Sexual & Asexual Reproduction

Reproduction in bacteria is just like any other organism, to continue their species.

• Bacteria are microbes with only one cell.
• The cell structure is simpler than that of other species since there is no nucleus or membrane-bound organelles.
• Bacteria are classified as prokaryotes because they are unicellular and don't have well-organized cells.
• Each division cycle (generation) of a bacterial population produces two cells, four cells, eight cells, sixteen cells, 32 cells, and so on.
• They do, however, show both sexual and asexual reproduction. 
• An organism that reproduces sexually combines the genetic information from both parents and is genetically unique.
• Asexual reproduction occurs when one parent replicates itself to produce genetically identical offspring.

Key Terms: Bacteria, Sexual reproduction, Asexual reproduction, Microorganism, Prokaryotes, Unicellular organism, Fragmentation

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Reproduction in Bacteria

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Bacteria, like all other organisms, reproduce in order to perpetuate their species.

• Bacteria are classified as prokaryotes because they are unicellular and lack a well-organized cell.
• They do, however, exhibit both sexual and asexual modes of reproduction.

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Asexual Reproduction in Bacteria

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There are five methods of asexual reproduction in bacteria. They are as follows:

Binary Fission

A single bacterial cell divides into two daughter cells during binary fission.

• The bacterial cell initially reaches critical mass in terms of structure and cell components.
• The bacteria's circular double-stranded DNA replicates, resulting in the formation of new complementary strands.
• As the duplicated DNA strands move to opposite poles of the cell, a transverse septum begins to form in the central region.
• This dividing wall gradually bisects the cytoplasm, ultimately separating the two new daughter cells, and completing the process of binary fission.
• It is a quick process that takes only a few minutes to finish.

Conidia-based reproduction

Conidia are formed in filamentous bacteria such as Streptomyces by the creation of a transverse septum at the apex of the filament.

• The component of the cell that contains the conidia is known as the conidiophore, and once separated from the mother cell, it germinates in a suitable substrate, giving rise to new mycelium.
• This sort of asexual reproduction is referred to as fragmentation.

Budding

In this form of reproduction, the bacterial cell develops a tiny bulge on one side that grows in size over time.

• At the same time, the nucleus divides, with one half with some cytoplasm entering the swelling and the other remaining with the mother cell.
• The bud is the name given to the protrusion, which is eventually separated from the mother cell by a partition wall.
• In bacteria, this type of reproduction is also known as vegetative reproduction.
• Rhodomicrobium vannielii is an example.

Cyst formation for reproduction

Cysts are the resting structure during adverse conditions, generated by the deposition of extra layers around the mother cell.

• When the conditions are favourable again, the mother cell resumes its regular behaviour.
• Azotobacter is a good example.

Endospore formation for reproduction

Endospores are generated in a bacterial cell amid severe conditions such as desiccation and hunger.

• They have a central protoplast and a core that contains DNA, ribosomes, enzymes, and the t-RNA, all of which are required for the development of a new cell.
• In one bacterial cell, only one endospore is generated, and upon germination, it gives rise to a new bacterial cell.
• However, genetic recombination is not observed in asexual reproduction, which is why sexual reproduction is so important in the survival of a bacterial species.
• This is because, during sexual reproduction, genetic material is shared between two cells, facilitating genetic recombination and causing genetic drift in a bacteria's species.

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Sexual Reproduction in Bacteria

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It was once thought that sexual reproduction did not occur in bacteria.

• Lederberg and Tatum (1946) demonstrated that bacteria can reproduce sexually.
• They were given the Nobel Prize for this finding.

Bacteria reproduce sexually in three methods, which are as follows:

Transformation

During transformation, a bacterium absorbs DNA from its surroundings as well as DNA released by other bacteria.

• Griffith identified the phenomenon in 1928, and Avery worked out the mechanism in 1944.
• The DNA of a capsulated bacteria is transferred into a non-capsulated organism through this process.
• A plasmid is a circular piece of DNA.
• The plasmid can be replicated in the recipient cell and passed on to offspring.

Transduction

Foreign genes are transmitted into a bacterial cell with the help of a virus in this sort of sexual reproduction of bacteria.

• These viruses are known as bacteriophages, and they are not dangerous.
• The virus works as a vector for gene transfer from one host to another.
• Transducing bacteriophages may contain the same genes, in which case the reproduction process is referred to as restricted transduction.
• They can also convey various genes at different times, which is known as generalised transduction in the reproduction process.

Conjugation

Tatum and Lederberg identified this mechanism in Escherichia coli in 1946.

• They discovered that when two distinct types of nutritional mutants were cultivated together on a minimum medium, an occasional wild type was created.
• Bacteria that conjugate are dimorphic, which means they have two kinds of cells, one male (F+) or donor cell and one female (F-) or receiver cell.
• The male or donor cell has 1 to 4 sex pili on its surface as well as a fertility factor (transfer factor, sex factor) in its plasmid.
• It contains genes that produce sex pili as well as other characteristics required for gene transfer.
• Sex pili are slender protoplasmic outgrowths that range in size from one to four. 
• The sex pili and the fertility factor are not present in female or recipient cells.
• If these two types of cells come into contact, a male cell's pilus forms a protoplasmic bridge or conjugation tube with the female cell.
• The process takes 6-8 minutes to finish.
• These are the three methods of sexual reproduction in bacteria, and they introduce genetic variety in a bacterial species, which is vital for any species' survival and allows groups to adapt to environmental changes.

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Things to Remember

• Binary fission is one of the methods used by bacteria to reproduce.
• The bacteria, which is a single cell, divides into two identical daughter cells during this procedure.
• Lederberg and Tatum (1946) demonstrated that bacteria can reproduce sexually.
• There are two strains of gramme negative bacteria: F+ (with fertility factor and sex pili) and F– (without fertility factor and sex pili) (without fertility factor and sex pili).
• The process by which a single cell divides into two genetically identical cells is known as binary fission.
• Bacterial cells exist in 3 shapes: rod-shaped, spherical, and spiral.
• A cell wall, a cellular membrane, the cytoplasm, flagella, a nucleoid region, plasmids, and ribosomes are all common bacterial cell components.
• Recombination, which includes the transfer of genes across cells, can help bacteria grow more genetically diverse because binary fission creates identical cells.