Name the cell which is responsible for nitrogen fixation in cyanobacteria

Above: a computer model of the filamentous cyanobacterium Oscillatoria . Three filaments are shown, each filament being a chain of cells (the cells being disc-like in Oscillatoria ). Cyanobacteria , also called blue-green algae, are a major group of photosynthetic bacteria. Their photosynthetic pigments give them their blue-green colouration (though sometimes other pigments mask this as some forms are orange or red in colour). The humble cyanobacteria dominated life on Earth for an immense period of time, from about 3 billion years ago to 500 million years ago - what could be called the Age of the Cyanobacteria. This age was crucial for the development of animal and plant life on Earth, since during this time the cyanobacteria created the first oxygen atmosphere. They are still widespread, though often overlooked. Their varied forms, vibrant colours and, in some cases, their graceful gliding movements make them beautiful subjects for the microscope. On close examination, they prove to be much more sophisticated and complex than first impressions might suggest. The internal structure of a typical cyanobacterium is shown below: See also: algal bodies . As prokaryotes, the blue-greens have no nuclear envelope and no true nucleus, instead the DNA is circular and free in the cytosol (cytosol = liquid component of the cytoplasm), though intricately folded and attached to special scaffolding proteins. Typical of bacteria, the DNA is often confined to a central region of the cell,...

Microorganisms help to increase the soil nutritional quality, as they are able to decompose organic matter. From soil, plants get nutrition for their growth and development. Along with microorganism, many fungi and algae also perform such functions. Algal cells are natural fertilizer and nowadays it is used worldwide, without any side effect, Algal cells have specific cells called heterocyst and are the site of nitrogen fixation. Algae are able to convert unavailable dinitrogen into bioavailable ammonia. Anabaena, Nostoc, and many other cyanobacteria (blue green algae, BGA) are able to fix atmospheric nitrogen. Keywords • Nitrogen fixation • Cyanobacteria • Nitrogenase • Nitrogen cycle • Heterocyst • Bergman B, Gallon JR, Rai AN, Stal LJ (1997) N 2 fixation by non-heterocystous cyanobacteria. FEMS Microbiol Rev 19:139–185 • Bray CM (1983) Nitrogen metabolism in plants. Longman Group Ltd, Harlow • Burk D, Lineweaver H, Horner CKJ (1934) The specific influence of acidity on the mechanism of nitrogen fixation by azotobacter. Bacteriology 27:325 • Canfield DE, Glazer AN, Falkowski PG (2010) The evolution and future of earth’s nitrogen cycle. Science 330:192 • Carpenter EJ, Price CC (1976) Marine Oscillatoria (Trichodesmium): explanation for aerobic nitrogen fixation without heterocysts. Science 191(4233):1278–1280 • Castenholz RW (2001) Cyanobacteria. In: Boone DR, Castenholz RW (eds) Bergey’s manual of systematic bacteriology, vol 1, 2nd edn. Springer, New York, pp 473–487 • ...

When people think of bacteria, they usually think of germs—disease-causing agents that threaten human health. In reality, they make life on Earth possible. One group of bacteria—the cyanobacteria—has completely transformed Earth’s environment through their long history. Three billion years ago, ancestors of cyanobacteria infused Earth’s ancient atmosphere with the byproduct of their photosynthesis—oxygen—changing the chemistry of the planet and setting the stage for entirely new oxygen-breathing life forms to evolve. Without the cyanobacteria, the life we see around us, including humans, simply wouldn’t be here. Before 1970, cyanobacteria were known to occur widely in fresh water and terrestrial habitats, but they were thought to be relatively unimportant in the modern oceans. This perception changed dramatically in the late 1970s and 1980s with the discovery of photosynthetic picoplankton by scientists at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology. Tiny members of this group of newly discovered cyanobacteria, Synechococcus and Prochlorococcus, turn out to be the most abundant organisms on the planet today. They are at the base of the ocean’s food chain, making air, light, and water into food for other life. Today, exploiting new biotechnological techniques, we are exploring their genes and uncovering the secrets of these extraordinary organisms. An unexpected glow In 1977, I was on the Atlantis II in the Arabian Sea with WHOI mi...

Nitrogen assimilation is strictly regulated in cyanobacteria. In an inorganic nitrogen-deficient environment, some vegetative cells of the cyanobacterium Anabaena differentiate into heterocysts. We assessed the photosynthesis and nitrogen-fixing capacities of heterocysts and vegetative cells, respectively, at the transcriptome level. RNA extracted from nitrogen-replete vegetative cells (NVs), nitrogen-deprived vegetative cells (NDVs), and nitrogen-deprived heterocysts (NDHs) in Anabaena sp. strain PCC 7120 was evaluated by transcriptome sequencing. Paired comparisons of NVs vs. NDHs, NVs vs. NDVs, and NDVs vs. NDHs revealed 2,044 differentially expressed genes (DEGs). Kyoto Encyclopedia of Genes and Genomes enrichment analysis of the DEGs showed that carbon fixation in photosynthetic organisms and several nitrogen metabolism-related pathways were significantly enriched. Synthesis of Gvp (Gas vesicle synthesis protein gene) in NVs was blocked by nitrogen deprivation, which may cause Anabaena cells to sink and promote nitrogen fixation under anaerobic conditions; in contrast, heterocysts may perform photosynthesis under nitrogen deprivation conditions, whereas the nitrogen fixation capability of vegetative cells was promoted by nitrogen deprivation. Immunofluorescence analysis of nitrogenase iron protein suggested that the nitrogen fixation capability of vegetative cells was promoted by nitrogen deprivation. Our findings provide insight into the molecular mechanisms underlyi...