Reproduction in Bacteria: Reproduction in Bacteria is primarily done by binary fission, an asexual process whereby a single cell divides into two. Under ideal conditions some bacterial species may divide every 10–15 minutes—a doubling of the population at these time intervals. Eukaryotic microorganisms reproduce by a variety of processes, both asexual and sexual. Some require multiple hosts or carriers (vectors) to complete their life cycles. Viruses, on the other hand, are produced by the host cell that they infect but are not capable of self-reproduction.
Reproduction in Bacteria just like any other organism, bacteria also reproduce to continue their species. Since they are unicellular and do not have a well-organized cell, bacteria have been grouped under prokaryotes. A bacterial population grows in a geometric or exponential fashion, with each division cycle (generation) producing two cells, four cells, eight cells, sixteen cells, 32 cells, and so on. However, they do show both sexual and asexual means of reproduction. In this topic, we will have a brief overview of all types of means of reproduction in bacteria.
Methods of Reproduction in Bacteria
There are five following types of Asexual reproduction:
- Binary fission
- Reproduction through conidia
- Reproduction through cyst formation
- Reproduction through endospore formation
1. Binary Fission: In binary fission, single cell divides into two equal cells. Initially the bacterial cell reaches a critical mass in its structure and cellular constituents. The circular double stranded DNA of bacteria undergoes replication, where both the strands separate and new complementary strands are formed on the original strands — results in the formation of two identical double stranded DNA. The new double stranded DNA molecule i.e., incipient nuclei, are then distributed into two poles of the dividing cell (no spindle formation takes place like mitotic division). A transverse septum develops in the middle region of the cell, which separates the two daughter cells. The binary fission is a rapid process and cell undergoes division at an interval of 20-30 minutes. The division becomes gradually slow after certain time due to accumulation of toxic substance and exhaustion of nutrients.
2. Reproduction through conidia: The formation of conidia takes place in filamentous bacteria such as Streptomyces through the formation of a transverse septum at the apex of the filament. The part bearing the conidia is called the conidiophore and after it is detached from the mother cell, in a suitable substratum it germinates giving rise to new mycelium. This type of asexual reproduction is also called fragmentation. Conidia production can be seen in filamentous bacteria such as Streptomyces. Conidia are small, chain-like, spherical, spore-like entities created by a transverse wall at the terminals of filaments. Conidiophore is the portion of the filament that contains conidia. Each conidium detaches from the mother and germinates in an appropriate substratum, producing a new mycelium.
3. Budding: The bacterial cell develops small swelling at one side which gradually increases in size. Simultaneously the nucleus undergoes division, where one remains with the mother and other one with some cytoplasm goes to the swelling. This outgrowth is the bud, which gets separated from the mother by partition wall, e.g., Hyphomicrobium vulgare, Rhodomicrobium vannielia, etc.
4. Reproduction through cyst formation: Cysts are formed by the deposition of additional layers around the mother cell and are the resting structure during unfavorable conditions. When conditions are favorable again, the mother cell behaves like its normal self again. Cysts are the mother bacterium cell’s inactive or resting stage. Cysts are generated when an extra layer is deposited around the mother wall. The cell’s metabolic process has slowed at this point. When bacteria find a favourable environment, they use a process called excystation to break down the cyst’s wall and germinate to generate a new bacterium. Cysts’ primary job is to protect the body from harmful environmental changes.
5. Reproduction through Endospore formation: Endospore are resting spores formed in some gram positive bacteria (Bacillus and Clostridium) during unfavourable conditions. They are formed within the cells. During this process a part of the protoplast becomes concentrated around the chromosome. A hard resistant wall is secreted around it. The rest of the bacterial cell degenerates; Endospore are very resistant to extreme physical conditions and chemicals. During favourable conditions the spore wall gets ruptured and the protoplasmic mass gives rise to a new
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