Bacteria are the immortal organisms on the earth. They reproduce instead of being dead. They reproduce by both
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 duties on the earth 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 condition, they convert to spores.
When the times are favorable, they emerge out 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 organism, bacteria have many methods of reproduction.
l. Asexual reproduction.
a. Binary fission.
b. Spore formation.
2. Sexual reproduction
Asexual reproduction: This happens by simple cleavage of the cell. This is of two types viz. binary fission and endospores. Here a single bacteria undergoes division to two new bacterial cells. This the most common process.
a) Binary fission: This is the most common method of reproduction. This occurs during favorable conditions. Here a single bacteria can split into two bacteria.
This process involves many intermediate steps. It occurs every 20 minutes once. Hence we can notice that bacteria double their population every half hour or so.
b) Endospores: During unfavorable condition like drought, bacteria undergo spore formation. They cover themselves with a hard coat which is rigid and resistant to extreme conditions. When the conditions are favorable, spores break open to release bacteria. Ec: Clostridium tetani bacteria shows it.
Sexual reproduction: 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 to be helpful to develop healthier offspring than that of asexual reproduction. The combination of gametes occurs by three methods like
a) Transformation: Here the naked DNA strands from the surrounding is taken up by the bacteria. Then it is incorporated into its genome. The phenomenon was discovered by Griffith in 1928 in diplococcus pneumonia bacteria. This transformation occurs inside the body, in the soil and marine environments. It is seen bacteria like streptococcus, Bacillus, azotobacter, and Pseudomonas.
b) Conjugation: 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 are the sexual appendages of bacterial cell.
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
c) Transduction: Here the genetic material from one bacteria is transferred to another with the help of bacteriophage. Bacteriophages are a type of virus which uses the bacterial genetic machinery to synthesize its own genetic material. So when this virus transfers from one bacteria to another, transduction takes place. Ex: in salmonella typhii bacteria.
When the virus multiplies inside a bacterial cell, bacterial DNA fragments are incorporated in the newly formed virus particles. When these virus particles or phages infect another bacteria, the DNA of first bacteria is transferred to 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 methods of reproduction, it is possible for humans to kill disease-causing bacteria by using antibiotics. These anti-biotics intervene in some part of the reproductive cycle and arrest their growth and multiplication.