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Summary Molecular biology has provided new tools to decipher genetic information and can be used in attempts to reconstruct the evolution of organisms and improve their taxonomy. In the cyanobacteria, the use of molecular methods to study the genotypic relationships is underway, and initial results are promising. Different chemotaxonomic and macromolecular techniques are reviewed and their usefulness...
Summary The initial interest in the phycoerythrin-containing picoplanktonic cyanobacteria, assigned to the genus Synechococcus, stemmed directly from a recognition of their considerable contribution to marine primary productivity, as well as to their widespread distribution in an environment hitherto characterized by its relative paucity of cyanobacteria. However, recent work has increasingly indicated...
Summary The interest in Prochlorophytes (Oxychlorobacteria) was originally boosted by the endosymbiont theory on chloroplast evolution. The first organism of this type: Prochloron didemni, was described as a procaryote performing oxygenic photosynthesis and containing both Chls a andb. The combination ofthose two pigments was until then only characteristic of Chlorophyte chloroplasts. The prochlorophytes...
Summary In a number of systematically unrelated eucaryotes, plastid-like organelles, termed cyanelles, are found which resemble present day cyanobacteria in morphology, biochemical organization of their photosynthetic apparatus, and in the presence of a peptidoglycan wall. The existence of cyanelles in species of different systematic position indicates repeated invasions of heterotrophically living...
Summary Plasmids from extant plants exhibit considerable diversity in morphological and biochemical characters. Although most authors have agreed on xenogenous (endosymbiotic) rather than autogenous origins of plastids (discussed by Doolittle (1982) in ‘The Biology of Cyanobacteria’), details concerning the endosymbiotic events remain unresolved. In the eleven years since ‘The Biology of Cyanobacteria’,...
Summary In cyanobacteria the outer membrane, plasma membrane and thylakoid membrane represent three structurally and functionally distinct membranes. Common themes are emerging from studies of thylakoid membranes which show that the major functional components, including Photosystem I, Photosystem II, cytochrome b6f, NADH dehydrogenase, cytochrome oxidase, and ATP synthase, exist as multisubunit...
Summary Phycobilisomes serve as the primary light-harvesting antennae for Photosystem II in cyanobacteria and red algae. These supramolecular complexes are primarily composed of phycobiliproteins, a brilliantly colored family of water-soluble proteins bearing covalently attached, open-chain tetrapyrroles known as phycobilins. In addition, phycobilisomes also contain smaller amounts ‘linker polypeptides,’...
Summary Oxygenic photosynthesis occurs in plants, green algae, and procaryotic cyanobacteria.Two chlorophyll-containing photosystems cooperate to transfer electrons from water to NADP+. Photosystem II is the membrane protein complex that carries out the light-catalyzed oxidation of water and reduction of plastoquinone. The reaction center is composed ofboth intrinsic and extrinsic proteins; the prosthetic...
Summary The plastoquinol-cytochrome c553/plastocyanin oxidoreductase (Cyt b6f complex) catalyzes the rate limiting, quinol-oxidation step in oxygenic photosynthesis. Overall, it transfers electrons between the two photochemical reaction centers (PS II and PS I), is required for cyclic electron flow around PS I, and establishes a transmembrane gradient of protons for ATP synthesis. Four polypeptides...
Summary The Photosystem I (PS I) complex in cyanobacteria functions most typically as a light-driven, cytochrome c6:ferredoxin oxidoreductase. The adaptability of cyanobacteria to conditions of nutrient availability allows cytochrome c6 to be replaced by plastocyanin when copper is plentiful, and ferredoxin to be replaced by flavodoxin when iron is limiting. These changes, however, do not lead to...
Summary The structure and mechanism of the F1F0-ATPase from cyanobacteria shares several characteristics with the chloroplast enzyme but also resembles a bacterial ATPase in many ways. The overall subunit composition and organization of the enzyme appear closely similar in all organisms. The F1 substructure is composed of three heterodimers of α and β subunits in which the β subunits are some what...
Summary This review covers only a fraction of the area of one written a dozen years ago on photosynthesis in cyanobacteria (Ho and Krogmann, 1982) yet it cites many more references than that earlier work. The power of reductionist laboratory science has increased immensely in the intervening years. The soluble electron transfer catalysts of photosynthesis have received disproportionate attention since...
Summary Cyanobacterial respiration is unique in several respects. Oxygenic photosynthesis and aerobic respiration are not separated in different organelles as in plants, but are active in the same compartment. Moreover, at least some cyanobacteria contain two distinct and complete respiratory chains, with one being found in each of their bioenergetically active membranes: the cell membrane and the...
Summary Carbon dioxide is a greenhouse gas whose accumulation in the biosphere has been the cause for increasing concern. CO2 is also the source for virtually all organic carbon on Earth and its efficient assimilation is directly related to agricultural productivity.As organisms which often depend on the reduction and assimilation of CO2 as their prime source ofcarbon, cyanobacteria have become important...
Summary The ability of cyanobacteria to adapt to a wide range of ambient CO2 concentrations involves modulation of the activity of an inorganic carbon-concentrating mechanism (CCM), as well as other changes at various cellular levels including the biosynthetic pathway of purines. Studies of high-CO2-requiring mutants have identified several of the genes involved in the operation of the CCM and in...
Summary The element nitrogen (N) constitutes about 5–10% of the dry weight of a cyanobacterial cell. The purpose of this chapter is to review the assimilatory pathways which in free-living cyanobacteria lead from different extracellular N-sources to cellular N-containing components. Inorganic nitrogen in the form of ammonium is incorporated into glutamine and glutamate via the glutamine synthetase/glutamate...
Summary Cyanobacteria are versatile tetrapyrrole synthesizers that are able to produce end products representing all major branches of the tetrapyrrole biosynthetic pathway: hemes, chlorophylls, phycobilins, and siroheme. Although tetrapyrrole biosynthesis has not been characterized as extensively in cyanobacteria as in plants and anoxygenic photosynthetic bacteria, recent studies ofthe biochemistry...
Summary Carotenoids in cyanobacteria have two main functions: they serve as light-harvesting pigments in photosynthesis, and they protect against photooxidative damage. Carotenoids are generally hydrophobic isoprenoid compounds that are synthesized in membranes. They mostly accumulate in protein complexes in the photosynthetic membrane, in the cell membrane and in the cell wall. In addition to the...
Summary In recent years great strides have been made in developing genetic systems for the analysis of various aspects of cyanobacterial physiology and development. Transformation, electroporation and conjugation systems provide effective means for gene transfer in diverse cyanobacterial strains. Gene transfer, combined with the ability to clone and inactivate genes in cyanobacteria, has opened the...
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