They lack a membrane-bound nucleus. Nevertheless, they have microcompartments. For instance, carboxysome is a compartmentalized cage-like structure surrounded by a protein shell.
Apart from photosynthesis, the thylakoids are also involved in cellular respiration. While the thylakoid machinery for electron transport is used for photosynthesis in the light during the day it is then used for respiration in the dark at night.
Filamentous species may differentiate into vegetative cells photosynthetic cells , akinetes spores resistant to harsh environmental conditions , or to heterocysts cells capable of nitrogen fixation by producing the enzyme nitrogenase. Apart from photosynthesis, cyanobacteria are capable of nitrogen fixation through heterocysts.
Some of them are nonmotile whereas others can move by gliding motility. Motile filaments of cyanobacterial cells are called hormogonia. Individual cells may break away from this filament to start a new colony elsewhere. In order to float, they form gas vesicle a vesicle bounded by a protein sheath and not by a lipid membrane.
Cyanobacteria reproduce by binary fission. Certain cyanobacteria are nitrogen-fixing organisms. Anabaena is an example. They can fix the atmospheric nitrogen into another form e. Cyanobacteria can fix atmospheric nitrogen through transforming into specialized cells called heterocysts. Heterocyst formation occurs when the environment is anoxic and fixed nitrogen is scarce. Circadian rhythm was once thought to be an exclusive feature of eukaryotes.
Later on, scientists found that certain cyanobacteria also display circadian rhythm. According to endosymbiotic theory, eukaryotes that have acquired the ability to photosynthesize are those that have evolved from the primitive eukaryotes that ingested primitive photosynthetic prokaryotes, such as cyanobacteria. A primary endosymbiotic event led to the evolution of the three primary endosymbiotic eukaryotes: green plants, red algae, and glaucophytes. These three groups make up the monophyletic group, Archaeplastida.
The primitive cyanobacterial cell inside the eukaryote is theorized to have eventually become the plastid chloroplast that is known today. The chloroplast and the cyanobacterial cell seem to share common features, i. Following the primary endosymbiosis, secondary and tertiary endosymbiotic events ensued, and these are believed to have led to later lineages of photosynthetic eukaryotes.
Cyanobacteria are found in aquatic habitats and moist soil. Heterocysts are specialized cells harboring nitrogen fixation, a process by which atmospheric nitrogen N 2 is converted to a biologically useful form NH 3. This enables cyanobacteria to exploit ecosystems devoid of nitrogen compounds, including those located in polar, open ocean, and desert regions. Cyanobacterial nitrogen fixation can be a significant source of biologically available nitrogen in these ecosystems.
Cyanobacteria move by gliding, using mucilaginous excretions as propellant, or, in the case of planktonic genera, by altering buoyancy through gas vesicle formation and collapse. Cyanobacteria exhibit remarkable ecophysiological adaptations to global change. They tolerate desiccation , hypersalinity , hyperthermal, and high ultraviolet light conditions, often for many years.
Over their long evolutionary history, they have formed numerous endosymbiotic and mutualistic associations with microorganisms, higher plants, and animals, including lichens fungi , ferns, cycads, diatoms, seagrasses, sponges, and even polar bears.
Cyanobacteria have also exploited man-made pollution of aquatic environments, especially nutrient-stimulated primary productivity or eutrophication. Cyanobacterial blooms are highly visible, widespread indicators of eutrophication.
Because of the toxicity of some bloom taxa, blooms can pose serious water quality and animal and human health problems. Finally, the large contribution of cyanobacterial blooms to phytoplankton biomass and ecosystem nutrient fluxes can alter biogeochemical cycling and food web dynamics.
Describe the characteristics associated with Cyanobacteria including: cell types, forms of motility and metabolic properties. Cyanobacteria, also known as blue-green bacteria, blue-green algae, and Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early reducing atmosphere into an oxidizing one, which dramatically changed the composition of life forms on Earth by stimulating biodiversity and leading to the near-extinction of oxygen-intolerant organisms.
According to the endosymbiotic theory, chloroplasts in plants and eukaryotic algae have evolved from cyanobacterial ancestors via endosymbiosis. Cyanobacteria can be found in almost every terrestrial and aquatic habitat. Aquatic cyanobacteria are probably best known for the extensive and visible blooms that can form in both freshwater and the marine environment. These can have the appearance of blue-green paint or scum. The association of toxicity with such blooms has frequently led to the closure of recreational waters when blooms are observed.
Cyanobacteria include unicellular and colonial species. Colonies may form filaments, sheets, or even hollow balls. Some filamentous colonies show the ability to differentiate into several different cell types, including:. These molecules can be absorbed by plants and converted into protein and nucleic acids. Many cyanobacteria form motile filaments called hormogonia, that travel from the main biomass to bud and form new colonies elsewhere.
The cells in a hormogonium are often thinner than those found in the vegetative state, and the cells on either end of the motile chain may be tapered. To break away from the parent colony, a hormogonium often must tear a weaker filament cell, called a necridium.
Individual cells of a cyanobacterium typically have a thick, gelatinous cell wall.
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