Production of Small Reproductive Cells and Spores
Most bacteria divide by binary transverse fission. In this process two cells of comparable size and mirror-image symmetry are produced. The daughter cells receive about half of the material and energy of the parent cell, and the cell diameter remains unchanged throughout the division cycle. One possible strategy for reproduction would be to produce a small reproductive cell that would have the minimal requirements for independent growth. The mother cell in this instance would not commit so much of its resources to reproduction as would be required if the daughter cell were the same size as the parent cell. Two examples of cell division processes, budding and baeocyte production, are known in bacteria that result in the production of cells that are smaller than the parent. In addition, some bacteria produce special hardy cells referred to as endospores, cysts, or exospores that may be smaller than the parent cell.
Buds and Baeocytes. Many bacteria produce buds. Examples of budding bacteria are reported in the phylogenetic groups Proteobacteria (e.g., Hyphomicrobium, Prosthecomicrobium, Ancalomicrobium, Gemmiger, etc.) and Planctomycetes (Pirellula, Planctomyces, Gemmata, and Isosphaera ). However, in all groups reported above, the cell size of the mother cells is quite large, so although the bud diameters are smaller, they are still greater than 0.2 µm in diameter when they separate from their mother cells (Bergey’s Manual, 1989).
You are viewing: Which Is The Smallest Of The Major Groups Of Microorganisms
Read more : Which Statement Describes Enslaved Persons In Ancient Rome And Greece
Some Pleurocapsaen cyanobacteria undergo multiple fission to produce small cells referred to as baeocytes. However, those that have been reported are more than 1.0 µm in diameter (Waterbury and Stanier, 1978).
Endospores, Cysts, and Exospores. Endospores are special survival cells produced by some Gram-positive bacteria, particularly those that live in sediments, soil, and rock environments. The classical genera Bacillus and Clostridium are best known for endospore production, but others such as Sporobacillus also are known. The endospore contains DNA, ribosomes, and several layers of wall material referred to as a coat. The mature endospore is dehydrated and contains high concentrations of calcium and dipicolinic acid. Usually the endospore is somewhat smaller in diameter than its vegetative mother cell, but in some cases, such as Clostridium tetani (which causes tetanus), it is actually larger. However, none of the endospores reported is less than 0.25 µm in diameter (Bergey’s Manual, 1986).
Read more : Which Is An Example Of Evidence Spoliation
Cysts are produced as resting stages by some Gram-negative bacteria found in soils. Azotobacter species are one example. The myxobacteria also produce cysts termed microcysts or microspores. Cysts of both of these Proteobacterial groups are relatively large, ultimately larger than 0.25 µm, because they are formed from a vegetative cell by the addition of extra layers outside the cell wall.
Exospores or conidiospores are produced by many of high mol% G + C Gram-positive bacteria such as Streptomyces spp. These specialized cells are produced in the aerial mycelium as a resistant dispersal reproductive cell. They are about the same diameter as the filament diameter, greater than 0.5 µm (Bergey’s Manual, 1989).
Source: https://t-tees.com
Category: WHICH
