Bacteria are the immortal organisms on the earth. They reproduce instead of being dead. They can reproduce by
a) Asexual reproduction
b) Sexual reproduction.
Bacteria reproduce very fast that a colony of bacteria will double in just half an hour.
Hence they can perform many earth-related duties, like scavenging the dead and waste.
In fermenting the molasses and rapid yield in biotechnology etc.
They can reproduce in many ways yet maintain genetic diversity and robustness.
In times of harsh conditions, they convert to spores.
When the times are favorable, they emerge as new offspring.
Thus they rarely die but keep on reproducing.
Hence we can see the development of resistance to drugs by some parasitic bacteria.
How do bacteria reproduce?
Unlike other organisms, bacteria have many methods of reproduction.
l. Asexual reproduction.
- Binary fission.
- Spore formation.
2. Sexual reproduction
- This happens by simple cleavage of the cell.
- This is of two types binary fission and endospores.
- Here a single bacteria undergo division into two new bacterial cells.
a) Binary fission
- This is the most common method of reproduction.
- This occurs during favorable conditions.
- Here each bacteria reproduce by binary fission and the parent cell is split into two identical daughter cells.
- This process involves many intermediate steps.
- It occurs every 20 minutes once.
- Hence we can notice that bacteria double their population every half hour.
- During unfavorable conditions like drought, bacteria undergo spore formation.
- They cover themselves with a hard coat that is rigid and resistant to extreme conditions.
- When the conditions are favorable, spores break open to release bacteria.
Example: Clostridium tetani bacteria follow this method.
- There is no true sexual reproduction. But the, reproduction happens by mutual exchange of gametes.
- In doing so, their chromosomes will be interchanged.
- This interchange is considered helpful in developing healthier offspring than that of asexual reproduction.
- The combination of gametes occurs by three methods
- Here, the bacteria take up the naked DNA strands from the surrounding.
- Then it is incorporated into its genome.
- Griffith discovered the phenomenon in 1928 in diplococcus pneumonia bacteria.
- This transformation occurs inside the body, in the soil and marine environments.
It is seen in bacteria like streptococcus, Bacillus, azotobacter, and Pseudomonas.
- This was discovered by Lederberg and Tatum in Escherichia coli.
- The donor type bacteria F+ binds with recipient type bacteria F- with the help of pili.
- Pili is the sexual appendages of bacterial cells.
- A conjugation tube is formed between two bacteria through pili.
- A part of the chromosome of one bacteria cell reaches the other.
- Sometimes entire chromosome of F+ passes into F-.
- The donor bacteria do not die and go for natural multiplication, while the recipient bacteria acquire new characters due to recombination.
Thus the genetic exchange occurs. Ex: E.Coli
- Here, the genetic material from one bacteria is transferred to another with the help of a bacteriophage.
- Bacteriophages are viruses that use bacterial genetic machinery to synthesize their own genetic material.
- So when this virus transfers from one bacteria to another, transduction occurs.
Ex: in Salmonella Typhi bacteria.
- When the virus multiplies inside a bacterial cell, bacterial DNA fragments are incorporated into the newly formed virus particles.
- When these virus particles or phages infect another bacteria, the DNA of the first bacteria is transferred here.
- This transferred DNA gets incorporated into the chromosome of the second bacteria. Thus the DNA gets transferred in between bacteria by a virus.
- Because of the above reproduction methods, anti-biotics can kill disease-causing bacteria.
These anti-biotics intervene in some parts of the reproductive cycle and arrest their growth and multiplication.