Asexual Reproduction
There is the involvement of a single parent i.e they are uniparental. Asexual reproduction does not result in the development of gametes. It is of the following types
A.Binary Fission B.Endospore formation C.Budding D.Conidia
Binary Fission
During fission, the cell lengthens and nuclear material is divided. In binary fission, DNA replication proceeds septum formation, the two resulting cells are mirror images of one another.
Note: Fission is characteristic of all types of bacteria and that is why they have been placed in the class Schizomycetes.
Endospore Formation
The endospores are intracellular resting cells and are formed during unfavourable conditions. During these conditions, the bacterial cytoplasm will aggregate and after that, the cytoplasm gets surrounded by a thick wall. this thick wall structure is formed inside the bacterial cell, it is known as Endospore. the origin of endospore in endogenous. the bacterial cell wall will break and endospore will be released. The endospore will continue in a resting stage as long as the conditions are unfavourable. It will function as a resting or perinating structure. But when the conditions become favourable the thick wall around the endospore is lost or removed. then the endospore starts germination. The endospores can tolerate low temperature as well as they can tolerate high temperature. They can tolerate low temperatures as low as -100 degrees, they can also tolerate high temperatures as high as 100 degrees.
Budding
The bacterial cell produces multiple outgrowths in this sort of multiplication. Other cell organelles go into these outgrowths, which are filled with cytoplasm. Buds are the name for these outgrowths.
Conidia
Conidia are formed in filamentous bacteria such as Streptomyces by the creation of a transverse septum at the filament’s apex. After detaching from the mother and coming into contact with an appropriate substratum, the conidium grows and generates new mycelium.
Sexual Reproduction in Bacteria
Sexuality in bacteria was first discovered by Tatum and Lederberg in 1947 in Escherichia coli. Gamete production and fusion are not present in bacteria. The only thing which happens in bacteria is genetic recombination. It means variation is there that does not involve gamete formation. Thus sexual reproduction in bacteria occurs by a method called Parasexuality. As a result, bacteria do not have true sexual reproduction; instead, genetic recombination occurs.
Genetic Recombination (Parasexuality)
There is no gamete formation, no gametic fusion only there is genetic recombination present in bacteria. Thus there is the transfer of genetic material from one bacteria to another bacteria, this method of genetic recombination is known as Parasexuality. This occurs in three ways
1.Transformation 2. Conjugation 3. Transduction
Transformation
A transformation is an unusual form of recombination in which the molecules of DNA that transport the cell’s genetic information from the donor to the recipient through the liquid medium in which they are growing. Research using laboratory mice. later in 1944, O.Avery, C.M.Macleod and M.McCarty demonstrated it in vitro. Griffith took Diplococcus bacteria and in the Diplococcus bacteria, he took two strains i.e Bacteria of the R-strain and Bacteria of the S-strain. Around the R-strain bacteria, the capsule is absent and the colonies which are produced give a rough appearance that is why they are called R-type bacteria. S-type bacteria are surrounded by a capsule, and the colonies they produce are smooth, which is why they are termed S-type bacteria. Now out of the two bacteria, R-strain bacteria is non-pathogenic i.e disease-causing potential is absent and S-strain bacteria are pathogenic i.e disease-causing ability is present.Now what Griffith did was he injected living R-type bacteria in the mice. The mice show survival.
Now he used heat-killed S-type bacteria and put them into mice, and he saw that the mice survived.
If the capsule is formed around the R-type bacteria then R-type bacteria gets converted into S-type bacteria. The conversion of R-type bacteria into S-type bacteria is known as Transformation. The transformation means change, the substance or chemical which is responsible for change he called it as transforming principle.
Conjugation
Conjugation was first discovered by Lederberg and Tatum and the experimental material which was utilized by them that is E.coli. In conjugation, there is the transfer of genetic material from one bacteria to another bacteria and it occurs with the help of a conjugation tube. In conjugation, they discuss the male-sterile method and female sterile method.
In the male-sterile method F+ cell interacts with the F- cell. In F- bacteria main DNA and Fplasmid is absent. So there is no formation of sex pilli. This F- bacteria is also known as female or recipient cells. With the help of sex pilli, the male and the female bacteria will join with the help of a conjugation tube. We know that the plasmid can show autonomous replication to form its copies. one of the copies of the F plasmid will be transferred to a female cell with the help of a conjugation tube. The transfer of plasmid is required only for one minute. but after a certain time duration, the conjugation tube breaks down to form two bacterial cells. F cell and F cell are the two types of cells that are made.
However, one cell was female before conjugation and becomes male after conjugation.it means female changed into male which means sexes are interchanged. The change of sex is known as sex duction. The transfer of male DNA is absent that is why it is known as the Male-sterile method. In the Hfr cell, there is main DNA and the plasmid is integrated with the main DNA i.e Episome. The cell is also called the Hfr cell or Metamale. It comes in contact with F- cell. The primary DNA is present in the F- cell, but the plasmid is not. The two cells come into touch with the help of a sex pilli and a conjugation tube.
In the main DNA, there is also an integrated plasmid that breaks down from one end and one bacterial cell, it will start moving from one to another cell with the help of a conjugation tube. For the transfer of plasmid, it needs a time of one minute but the transfer needs about 90- 100 minutes. one thing you should remember that the part of the main DNA which starts to transfer is also gets formed into the main DNA.it needs 90-100 minutes for transfer. The conjugation tube gets breaks down as it will not persistent for such a long time so only part of DNA is transferred. After the breakage, the two cells are separated. It has an Hfr cell and F- cell. The F-cell has the main DNA and also contain part of DNA of the main DNA which has transferred. The transferred DNA will integrate into the main DNA of the F- cell. The bacteria have their DNA called Endogenate, the bacteria also contain DNA of the other bacteria called Exogenate. Thus we can say that genetic recombination has occurred such type of condition is called Merozygote or Partial zygote. The change from male to female is absent. Thus we can say sex duction is absent but Genetic recombination is present. so we called this male fertile method, Recombination is only possible when the cell Hfr and the plasmid are integrated into it. that is why we called it a High-Frequency recombinant cell.
Transduction
It is first found by Lederberg and Zinder and the experimental material which was utilized by them is Salmonella, in this method of reproduction again transfer of genetic material from one bacteria to another bacteria and is assisted with the help of viruses. They use bacteriophage, this is a virus that infects bacteria. In viruses, there are two main components one is nucleic acid and protein coat. It has a head and tail. The nucleic acids are double-stranded and are covered with proteins. This is bacterial phage eating bacteria. Bacteriophage infects bacteria. Bacteriophage has infected bacteria and at the tip of the tail, there is the presence of an enzyme (lysozyme). This lysozyme can digest the wall that is made up of PG which is then digested by lysozyme. when the wall is digested there is the formation of a hole. This virus will drill a hole in the cell wall. Then the tail of the virus will contract due to which now the double-stranded DNA is released inside the cytoplasm of the bacteria. Now the bacterial cell has viral DNA and bacterial DNA. The viral DNA will integrate into the bacterial DNA .when viral DNA is present in integrated form this is known as Prophage or Provirus. when the DNA of bacteria starts replication along with bacterial DNA there is a replication of viral DNA. In the integrated condition of viral DNA into the main DNA of bacteria, the virus cannot harm bacteria. This type of bacteria that contain viral DNA is known as lysogenic bacteria. they are also known as template viruses and this type of life cycle of the virus is known as the lysogenic cycle. This viral DNA remains in the integrated condition but sometimes this viral DNA can come out from bacterial genetic material in two ways i.e symmetrical and Asymmetrical. But when it comes out it contains both the types of DNA i.e viral as well as bacterial DNA. It is known as Asymmetrical Excession. Virus DNA once it is out of the bacterial DNA it will utilize the machinery of the host i.e. bacteria will form an enzyme i.e Nuclease, which can digest bacterial DNA . once the bacterial DNA is degraded this virus utilize the machinery of bacteria it will form different body parts by utilizing the machinery of the host, it will form different body parts i.e head, tail along with that there is also small segments of bacterial DNA. These different body parts will assemble in bacterial cells to form a mature virus and will join inside the bacterial cell .i.e the head will join with the tail. It will also cause lysis of bacterial cell walls and viruses are released from the bacteria. This virus contains DNA of its own and along with that it also contains some segmental DNA of bacteria. This type of virus is known as transducing phage. when the virus kills the bacteria results in a lysis of bacteria. This type of cycle is known as the lytic cycle. This transducing phage which is released from the bacteria will also affect another bacteria.it shows integration inside the bacterial cell. The bacteria will have its DNA and the DNA of viruses have DNA of two types i.e. it has endogenate and exogenate conditions. Thus here it is genetic recombination.