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Azolia-Anabaena Symbiosis
Published in Peter M. Gresshoff, Molecular Biology of Symbiotic Nitrogen Fixation, 2018
In nitrogen-fixing prokaryotes, including A. azollae, biological nitrogen fixation is catalyzed by the nitrogenase enzyme complex which is composed of two components: the nitrogenase (called MoFe protein) and the nitrogenase reductase (called Fe protein).104 In the free-living Anabaena sp. PCC7120 these components are genetically determined by three genes: nifH, nifD, and nifK.105,106 Another nif gene (nifS) is required for maturation of the nitrogenase complex.106 In vegetative cells of Anabaena sp. PCC7120, nifK is separated from nifDH by an 11-kilobase (kb) DNA fragment.106 Golden et al.107 have recently demonstrated that this intervening region is excised in subsequent linking of the nifK and nifDH genes. Lammers et al.108 have shown that the 11-kb DNA element is excised by site-specific recombination events between directly repeated 11-base pair (bp) sequences at each of its ends, and encodes a gene, xisA, required for its own excision. A second rearrangement which leads to the excision of a circular DNA element from vegetative-cell DNA is also observed near nifS.107 All these findings, including organization of nitrogen-fixation genes and a developmentally regulated nifK /nif D gene rearrangement phenomenon, were shown only in the free-living Anabaena sp.107,109
Biology of microbes
Published in Philip A. Geis, Cosmetic Microbiology, 2006
The latter two are sometimes contaminants of personal care products, so we will touch briefly on nitrogen fixation. Realize, however, that nitrogen fixation is primarily a function of organisms that are not of concern to the cosmetic or drug microbiologist. Nitrogen fixation is the reduction of atmospheric gaseous nitrogen into ammonia by nitrogenase. It requires at least 6 electrons for reducing power and 12 ATP molecules.
An overview on cyanobacterial blooms and toxins production: their occurrence and influencing factors
Published in Toxin Reviews, 2022
Isaac Yaw Massey, Muwaffak Al osman, Fei Yang
It is well established that nitrogen fixation is an important feature of some cyanobacteria species and in terms of nutrition nitrogen-fixing, cyanobacteria are considered the most self-sufficient among other organisms. They are photoautotrophs that require only light energy, CO2, dinitrogen (N2), water and some minerals (Paerl and Huisman 2009, Paerl and Otten 2013, Paerl et al.2016, 2001). Heterocysts are specialized nitrogen-fixing cells. Heterocysts have thick cell wall, do not pose photosynthetic membrane and are larger, clearer and highly refractive under light microscope appearance. They may occur within the filament of photosynthetic cells or terminally on a filament (Paerl and Huisman 2009, Paerl and Otten 2013, Paerl et al.2016, 2001). Due to the differences in size, shape and location of heterocysts, they form a significant component in species identification. Within the heterocysts, the enzyme nitrogenase reduces molecular nitrogen to ammonia, which is incorporated into the amido group of glutamine. The thickened cell wall enables molecular oxygen to enter the cell, to be reduced (Bryant 1994, Paerl et al.2016, 2001), thus helping to maintain a highly reducing environment within the cell, necessary for nitrogen reduction.