Akinets and Heterocysts

An akinete is an enveloped, thick-walled, non-motile, dormant cell formed by filamentous, heterocyst-forming cyanobacteria under the order Nostocales and Stigonematales. Akinetes are resistant to cold and desiccation. They also accumulate and store various essential material, both of which allows the akinete to serve as a survival structure for up to many years. However, akinetes are not resistant to heat. Akinetes usually develop in strings with each cell differentiating after another and this occurs next to heterocysts if they are present. Development usually occurs during stationary phase and is triggered by unfavorable conditions such as insufficient light or nutrients, temperature, and saline levels in the environment. Once conditions become more favorable for growth, the akinete can then germinate back into a vegetative cell. Increased light intensity, nutrients availability, oxygen availability, and changes in salinity are important triggers for germination. In comparison to vegetative cells, akinetes are generally larger. This is associated with the accumulation of nucleic acids which is important for both dormancy and germination of the akinete. Despite being a resting cell, it is still capable of some metabolic activities such as photosynthesis, protein synthesis, and carbon fixation, albeit at significantly lower levels. Akinetes can remain dormant for extended periods of time. Studies have shown that some species could be cultured that were 18 and 64 years old. Akinete formation also influences the perennial blooms of cyanobacteria. Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as Nostoc punctiforme, Cylindrospermum stagnale, and Anabaena sphaerica. They fix nitrogen from dinitrogen (N2) in the air using the enzyme nitrogenase, in order to provide the cells in the filament with nitrogen for biosynthesis. Nitrogenase is inactivated by oxygen, so the heterocyst must create a microanaerobic environment. The heterocysts’ unique structure and physiology require a global change in gene expression. For example, heterocysts: - produce three additional cell walls, including one of glycolipid that forms a hydrophobic barrier to oxygen - produce nitrogenase and other proteins involved in nitrogen fixation - degrade photosystem II, which produces oxygen - up-regulate glycolytic enzymes - produce proteins that scavenge any remaining oxygen - contain polar plugs composed of cyanophycin which slows down cell-to-cell diffusion Cyanobacteria usually obtain a fixed carbon (carbohydrate) by photosynthesis. The lack of water-splitting in photosystem II prevents heterocysts from performing photosynthesis, so the vegetative cells provide them with carbohydrates, which is thought to be sucrose. The fixed carbon and nitrogen sources are exchanged through channels between the cells in the filament. Heterocysts maintain photosystem I, allowing them to generate ATP by cyclic photophosphorylation. Single heterocysts develop about every 9-15 cells, producing a one-dimensional pattern along the filament. The interval between heterocysts remains approximately constant even though the cells in the filament are dividing. The bacterial filament can be seen as a multicellular organism with two distinct yet interdependent cell types. Such behavior is highly unusual in prokaryotes and may have been the first example of multicellular patterning in evolution. Once a heterocyst has formed it cannot revert to a vegetative cell. Certain heterocyst-forming bacteria can differentiate into spore-like cells called akinetes or motile cells called hormogonia, making them the most phenotyptically versatile of all prokaryotes. The question: What is the name of the cells indicated by the arrows and what is their function? A) Akinete. Nitrogen fixation B) Heterocyst. Resting spore C) Akinete. Resting spore D) Heterocyst. Nitrogen fixation #NikolaysGeneticsLessons #Akinete #heterocysts #Botany #Genetics #blueGreenAlga #bacterialColony #cyanobacteria #microscopicLife #pondWater #microbes #cyanobacteriaUnderMicroscope #microscopicLifeDocumentary #microscopicLifeInPondWater #microscopicLifeInAPond #microbesForKids #pondLife #photosynthesis #CentralPark #microscope #Microcystis #cell #Dolichospermum #heterocyst #femaleScientist #microbiologist #microbiologyForKids #Aphanizomenon #ciliate #blueGreenAlgae