Bacterial replication

Replication in bacteria

1. Reproduction in bacteria By: Mrs. Mali Dhanashri R. Assistant professor, GES’s Sir Dr. M. S. Gosavi College of Pharmaceutical Education and Reseach

2. Reproduction Cell growth and reproduction by cell division are tightly linked in unicellular organisms. Bacteria are prokaryotic organisms that reproduce asexually. Bacteria grow to a fixed size and then reproduce through asexual reproduction Under optimal conditions, bacteria can grow and divide extremely rapidly, and bacterial populations can double as quickly as every 9.8 minutes. In cell division, two identical clone daughter cells are produced.

3. Types of reproduction Binary fission Budding Fragmentation Formation of Conidiospores or sporangiospores

4. Multiplication & divisional cycle Many bacterial cell multiply by binary fusion. Means, each individual cell increase in size until it is large enough to divide into two identical daughter cells. At that time of separation each daughter cell must be capable of growth & reproduction. While each daughter cell will automatically contain mRNA, rRNA, ribosomes, enzymes, cytochromes etc. from mother cell.

5. Binary fission Most prokaryotes reproduce by a process of binary fission In binary fission, the cell grows in volume until it divides in half to yield two identical daughter cells. Each daughter cell can continue to grow at the same rate as its parent. For this process to occur, the cell must grow over its entire surface until the time of cell division, when a new hemispherical pole forms at the division septum in the middle of the cell.

6. The septum grows inward from the plasma membrane along the midpoint and forms as the side wall which pinches inward, dividing the cell in two. In order for the cell to divide in half, the peptidoglycan structure must be different in the hemispherical cap than in the straight portion of the cell wall, and different wall-cross-linking enzymes must be active at the septum than elsewhere .

7. Binary fission begins with the single DNA molecule replicating and both copies attaching to the cell membrane. Next, the cell membrane begins to grow between the two DNA molecules. Once the bacterium just about doubles its original size, the cell membrane begins to pinch inward. A cell wall then forms between the two DNA molecules dividing the original cell into two identical daughter cells

8. Budding A group of environmental bacteria reproduces by budding. In this process a small bud forms at one end of the mother cell As growth proceeds, the size of the mother cell remains about constant, but the bud enlarges. When the bud is about the same size as the mother cell, it separates. This type of reproduction is analogous to that inbudding fungi, such as brewer’s yeast ( Saccharomyces cerevisiae ).

9. One difference between fission and budding is that, in the latter, the mother cell often has different properties from the offspring. Ex: In some strains, mother cells have a flagellum and are motile, whereas the daughter buds lack flagella.

10. Fragmentation Becteria may produce extensive filamentous growth. It reproduce by fragmentation of fillaments into small bacillary or coccoid cells. Each filament grows and forms new cells. E.g. Norcardia species.

11. Formation of Conidiospores Conidia formation takes place in filamentous bacteria like Streptomyces etc., by the formation of a transverse septum at the apex of the filament The part of this filament which bears conidia is called conidiophore. After detachment from the mother and getting contact with suitable substratum, the conidium germinates and gives rise to new mycelium.

12. Growth & Genetic exchange For many years it was thought that bacteria, unable to exchange genetic material and could only adapt and evolve through mutation of genes. The bacteria has profound ability to exchange and share DNA across diverse genera. This is of particular significance because it enables bacterial populations to adapt rapidly to changes in their environment,. This also help in the deployment of antibacterial chemicals and antibiotics. Three major process involved in genetic exchange…. Transformation Transduction Conjugation

13. Transformation Discovered by Frederick Griffith in 1928. The early work on the transfer of virulence in the pathogen Streptococcus pneumoniae . The stage for the research that first showed that DNA was the genetic material. Griffith found that if he boiled virulent bacteria and injected them into mice, the mice were not affected and no pneumococci could be recovered from the animals. When he injected a combination of killed virulent bacteria and a living nonvirulent strain, the mice died; moreover, he could recover living virulent bacteria from the dead mice. Griffith called this change of nonvirulent bacteria into virulent pathogens transformation.

14. Many bacteria can acquire new genes by taking up DNA molecules (ex: plasmid) from their surroundings. When bacteria undergo lysis , they release considerable amounts of DNA into the environment. This DNA may be picked up by a competent cell- one capable of taking up the DNA and undergoing a transformation. To be competent, bacteria must be in the logarithmic stage of growth, and a competence factor needed for the transformation must be present.

15. Transduction It is defined as a phenomenon causes genetic recombination in bacteria wherein DNA is carried from one specific bacterium to another by a bacteriophage . Bacterial viruses ( bacteriophages ) transfer DNA fragments from one bacterium (the donor) to another bacterium (the recipient). The viruses involved contain a strand of DNA enclosed in an outer coat of protein.

16. After a bacteriophage enters a bacterium, it may encourage the bacterium to make copies of the phage. At the conclusion of the process, the host bacterium undergoes lysis and releases new phages. This cycle is called the lytic cycle. Under other circumstances, the virus may attach to the bacterial chromosome and integrate its DNA into the bacterial DNA. It may remain here for a period of time before detaching and continuing its replicative process. This cycle is known as the lysogenic cycle.

17. Under these conditions, the virus does not destroy the host bacterium, but remains in a lysogenic condition with it. The virus is called a temperate phage, also known as a prophage . At a later time, the virus can detach, and the lytic cycle will ensue. It will express not only its genes, but also the genes acquired from the donor bacterium. As well as temperate phage will be active once again at a low frequency & phasing between temperate & lytic forms ensures the long-term survival of the virus.

18. Conjugation Conjugation is a natural process representing the early stages in a true sexually reproductive process. In that transcribed to produce singular viral elements, which cannot assemble or lyse the host cell. Such DNA strand are known as plasmids. Plasmids are circular & can either be integrated into the main chromosome, in which case they are replicated along with chromosome & passed to daughter cells or they are separate from it & can replicate independently. The simplest form of plasmid is F-factor (fertility factor). The cells containing an F-factor are designed F+

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