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Carbon dioxide fixation and its regulation in cyanobacteria

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... It has been stressed that there are areas of considerable homology within the respective large (226) and small (3,234,291,293,322) subunits of RuBPC/O from diverse sources. Of particular interest are the conserved sequences of the large subunit, within which are found residues important for catalysis or activation or both. ...
... Of particular interest is the lack of control over RuBPC/O synthesis in strains capable of dark heterotrophic growth (49), suggesting fundamental differences in the regulation of CO2 fixation in these organisms. This topic has been recently reviewed (322). ...
... strains 6308 and 6714, yielded rapid fluxes in the intracellular levels of phosphogluconate and other sugar phosphates (240,241), it was proposed that phosphogluconate might regulate CO2 fixation in 168 TABITA (327), a condition in which C02 fixation rapidly ceases. The intracellular level of RuBPC/0 active sites in cyanobacteria appears to be about 0.4 mM, perhaps lending credence to control by millimolar concentrations of intracellular phosphorylated metabolites (322). In situ RuBPC/0 assays, using toluene-permeabilized whole cells of Agmenellum quadruplicatum PR-6, Aphanocapsa sp. ...
... Much like Cm. vinosum (Hurlbert and Lascelles, 1963), the addition of organic compounds, particularly pyruvate, to photolithoautotrophically-grown (1.5% cultures, results in a drop in RubisCO activity. This effect was mimicked in autotrophic cultures after the concentration of was raised from the usual 1.5% to 6% (Jouanneau and Tabita, 1987). Immunological assays indicated that the levels of both form I and form II RubisCO protein remained constant during the time activity was lost, suggestive of some modulation of enzyme activity not related to protein degradation. ...
... Isolation and separation of inactivated from active enzyme further indicated that only the form I RubisCO was affected. Complicating things, the inactivated form I enzyme exhibited a marked propensity to become reactivated in vitro (Jouanneau and Tabita, 1987). Subsequent studies showed that inactivation occurred by some process that was reversible in vivo, since activity recovered soon after the cells consumed pyruvate or from the growth medium in the presence of protein synthesis inhibitors (Wang and Tabita, 1992a). ...
... vinosum enzyme does not require NADH for activity; in this respect the Cm. vinosum enzyme resembles the enzyme of oxygen-evolving photosynthetic organisms (Tabita, 1980;1987). Furthermore, the activity of enzymes isolated from all purple bacteria is negatively regulated by compounds such as AMP, 3-PGA, 3-PGAL, and PEP (Tabita, 1988). ...
Chapter
Purple photosynthetic bacteria exhibit great diversity in the metabolism of simple carbon compounds. In this chapter, the reactions and metabolic schemes that the organisms, particularly purple nonsulfur bacteria, employ to break down and/or assimilate one-carbon, two-carbon, three-carbon, and four-carbon compounds and sugars is examined. Knowledge of the biochemistry and physiology of carbon metabolism and its molecular control has benefited somewhat from the application of recombinant DNA approaches, yet there are significant gaps in our understanding of how catabolic and anabolic reaction sequences are integrated. By contrast, great advances have been made relative to the biochemistry of CO2 fixation, due primarily to recent enzymological, molecular, and structural studies of the key enzyme, Rubis CO. Indeed the enzyme from Rhodospirillum rubrum has become the paradigm for such work. The ability to prepare recombinant enzymes that catalyze additional key steps of CO2 fixation should result in similar advances concerning these proteins in the future. Facile genetic manipulation of mutant Rhodobacter and Rhodospirillum strains has already resulted in the uncovering of alternative CO2 assimilatory routes that replace the Calvin cycle, and prospects for gaining an understanding of the biochemistry and molecular control of both schemes should follow. The latter studies probably would not be possible with other organisms, further attesting to the versatility of the purple nonsulfur bacteria for investigating basic metabolic processes. This chapter considers the current state of our knowledge of carbon dioxide fixation and carbon metabolism in purple bacteria.
... Aquatic cyanobacteria are expert scavengers of CO 2 , utilising both free CO 2 and bicarbonate ions in the water (Tabita 1987). Green algae, on the other hand, preferentially take up bicarbonate and dehydrate it to CO 2 for use in photosynthesis. ...
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Thesis
Microcystins (MCYSTs) are cyclic heptapeptides that occur in several species of cyanobacteria. They potently inhibit protein phosphatases and are powerful hepatotoxins. This thesis examines the production of MCYST by Microcystis aeruginosa by determining changes in the intracellular MCYST quota (QMCYST) under various growth conditions. A novel protein phosphatase inhibition assay and an antibody detection method were developed for the detection and analysis of MCYST-producing strains of M. aeruginosa. However, for the routine analysis of MCYST an HPLC method was adopted as it permitted the quantification of specific MCYSTs. In N-limited chemostat-grown cells of M. aeruginosa MASH-01A19, QMCYST is strongly correlated with the growth rate (μ). For a specified growth rate, QMCYST can be predicted from the maximum (QMCYSTmax) and minimum (QMCYSTmin) intracellular MCYST quotas and the maximum growth rate (μmax). Since the cell volume was inversely related to μ, the intracellular concentration of MCYST was >10-fold greater in rapidly growing cells (μ = 0.96 d-1) than in slow growing cells (μ = 0.10 d-1). These data have important implications with respect to the toxicity of M. aeruginosa under field conditions. QMCYST was examined in batch cultures of M. aeruginosa MASH-01A19 to determine whether the relationship between QMCYST and its determinants μ, μmax, QMCYSTmin and QMCYSTmax, as they apply in N-limited chemostat cultures, also apply under other growth conditions. In batch cultures, μmax increased with temperature and irradiance but was not significantly affected by the level of P, S, N or Fe nutrition. QMCYST decreased as the level of S and Fe nutrition decreased but low P enhanced QMCYSTmin. QMCYSTmin decreased as the temperature and the irradiance increased but QMCYSTmin was not significantly affected by N nutrition. QMCYSTmax decreased as the level of S and N nutrition decreased but was not significantly affected by P and Fe nutrition. However, QMCYSTmax showed evidence of optima at intermediate temperature (26°C) and irradiance (40 μmol photons m-2 s-1). The strong effect of S and Fe nutrition on QMCYSTmin suggests that these elements play an important role in MCYST production. Due to the relationship between μ and QMCYST, environmental factors that affect μ will therefore affect QMCYST. The data in the thesis emphasise the importance of μ in determining QMCYST under a particular set of growth conditions and indicate that QMCYST can be predicted provided the parameters μmax, QMCYSTmax and QMCYSTmin are known for those conditions. The thesis also highlights the physiological inadequacies of determining MCYST relative to biomass indicators other than cell number.
... The presence of a biofilm can influence CaCO 3 precipitation through microbial metabolism and production of EPS ). Cyanobacterial photosynthesis generates carbonate ions and increases the saturation state of calcium carbonates (e.g., Bisset et al. 2008;Chafetz 1986;Chafetz and Buczynski 1992;Ludwig et al. 2005;Merz 1992;Paerl et al. 2001;Shiraishi et al. 2010;Tabita 1987;Verrecchia et al. 1995). However, this effect is inconsistent with the observation that aragonite precipitation was scarce during the daytime ( Figures 5A2, and 5B2 and 5F2). ...
Article
Lamina-forming processes of moderately thermophilic (∼55°C) unicellular cyanobacteria were identified for the carbonate travertine in the Myoken Hot Spring, Kagoshima Prefecture, southwestern Japan. Continuous 28-h monitoring of surface textures clearly showed a diurnal pattern in sub-millimeter order lamination, comprised of daytime dark colored aragonite layers, and night-time light colored calcite layers. The layering was controlled principally by daily cycles of unicellular cyanobacteria closely related to Thermosynechococcus elongatus BP-1. During a day, cyanobacteria migrated to the surface, and formed a dark green biofilm, in which CaCO3 is precipitated as radial aggregates of needle aragonite. After sunset, calcite precipitation formed dendritic aggregates of rhombic crystals that cover the biofilm. Physicochemical conditions of the ambient water were stable throughout a day; therefore CaCO3 polymorphs (aragonite/calcite) were controlled by the presence/absence of certain microbial effects, such as extracellular polymeric substances secreted by cyanobacteria. When travertine growth reached the water level, a yellow-green microbial mat developed on the subaerially exposed surface. Here, filamentous cyanobacteria joined in the microbial community under lowered temperature (∼40°C). Aragonite crystal precipitation occurring in the microbial mat supported the microbial effects on CaCO3 polymorphs. Geomicrobiological processes, effects, and the environmental conditions demonstrated in this travertine provide insights into a further understand of microbial textures in ancient carbonate sediments.
... Several phosphorylated metabolites, such as RBP, 2-carboxyarabinitol monophosphate (CA1P) or 6-phosphogluconate have been described as important inhibitors to Rubisco activity under certain conditions (Li and Tabita 1994). In that way, 6-phosphogluconate is one of the most effective in regulating both the partially active and the fully activated enzyme in the cell (Tabita 1987) and it is known that this effect is mediated by the small subunit of the Rubisco (Li and Tabita 1994). ...
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Article
The cyanobacterium Anabaena variabilis ATCC 29413 grown at low CO2 concentration under mixotrophic conditions with fructose showed a repression in the ability to fix inorganic carbon. This repression was not due to a diminution in the ability to transport external inorganic carbon but could be explained by a decrease of two enzymatic activities involved in the assimilation of inorganic carbon: carbonic anhydrase and Rubisco. Carbonic anhydrase activity was close to 50% lower in amixtrophis than in autotrophic cells. Moreover growth under mixotrophic conditions reduced Rubisco activity at all dissolved inorganic carbon concentrations assayed (5-60 mM). Maximum Rubisco activity (Vmax) decreased from 4.7 μmol CO2 mg protein-1 h-1 in autotrophic cells to 2.3 μmol CO2 mg protein-1 h-1 in mixotrophic cells. No significant differencess in Km (Ci) between autotrophic and mixotrophic cells were however observed. The possible mechanisms involved in the inhibition of Rubisco are discussed.
... They fix C0 2 via the Calvin cycle. Some are capable of limited heterotrophic growth, but C0 2 is the preferred source of C for all species (Tabita 1987). Some cyanobacteria can fix nitrogen in addition to carbon. ...
... (3)). HCO 3 − is transported into the cyanobacterial cell as a source of inorganic carbon for photosynthesis and converted to CO 2 by the carbonic anhydrase enzyme (Tabita, 1987;Merz, 1992;Verrecchia et al., 1995;Badger, 2001). When cyanobacteria convert HCO 3 − into CO 2 , OH − is released in the exopolymeric sheath environment, which results in an increase of carbonate in solution (see Section 4.2.1). ...
Article
Microbial communities are situated at the interface between the biosphere, the lithosphere and the hydrosphere. These microbes are key players in the global carbon cycle, where they influence the balance between the organic and inorganic carbon reservoirs. Microbial populations can be organized in microbial mats, which can be defined as organosedimentary biofilms that are dominated by cyanobacteria, and exhibit tight coupling of element cycles. Complex interactions between mat microbes and their surrounding environment can result in the precipitation of carbonate minerals. This process refers as ‘organomineralization sensu lato' (Dupraz et al. in press), which differs from ‘biomineralization’ (e.g., in shells and bones) by lacking genetic control on the mineral product. Organomineralization can be: (1) active, when microbial metabolic reactions are responsible for the precipitation (“biologically-induced” mineralization) or (2) passive, when mineralization within a microbial organic matrix is environmentally driven (e.g., through degassing or desiccation) (“biologically-influenced” mineralization). Studying microbe-mineral interactions is essential to many emerging fields of the biogeoscience, such as the study of life in extreme environments (e.g, deep biosphere), the origin of life, the search for traces of extraterrestrial life or the seek of new carbon sink. This research approach combines sedimentology, biogeochemistry and microbiology. Two tightly coupled components that control carbonate organomineralization s.l.: (1) the alkalinity engine and (2) the extracellular organic matter (EOM), which is ultimately the location of mineral nucleation. Carbonate alkalinity can be altered both by microbial metabolism and environmental factors. In microbial mats, the net accumulation of carbonate minerals often reflect the balance between metabolic activities that consume/produce CO2 and/or organic acids. For example, photosynthesis and sulfate reduction will increase carbonate alkalinity and the potential of precipitation, whereas aerobic respiration and sulfide oxidation will promote carbonate dissolution. The EOM is composed of two main carbon pools: the high molecular weight extracellular polymeric substances (EPS) and the low molecular weight organic carbon compounds (LMW-OC). Both pools play a critical role in carbonate precipitation by providing Ca2+ and CO32- as well as a nucleation template for mineral growth. EOM contains several negatively charged functional groups, which, depending on the pH, can be deprotonated (each group has unique pK value(s)) and, thus, bind cations. This binding capacity can deplete the surrounding environment of cations (e.g., Ca2+, Mg2+) and, thus, inhibits carbonate precipitation. Therefore, organomineralization is only possible if the inhibition potential is reduced through (1) oversaturation of the EOM binding capacity or (2) EOM degradation.
... (3)). HCO 3 − is transported into the cyanobacterial cell as a source of inorganic carbon for photosynthesis and converted to CO 2 by the carbonic anhydrase enzyme (Tabita, 1987;Merz, 1992;Verrecchia et al., 1995;Badger, 2001). When cyanobacteria convert HCO 3 − into CO 2 , OH − is released in the exopolymeric sheath environment, which results in an increase of carbonate in solution (see Section 4.2.1). ...
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Article
Microbial mats are ecosystems that arguably greatly affected the conditions of the biosphere on Earth through geological time. These laminated organosedimentary systems, which date back to > 3.4 Ga bp, are characterized by high metabolic rates, and coupled to this, rapid cycling of major elements on very small (mm-µm) scales. The activity of the mat communities has changed Earth's redox conditions (i.e. oxidation state) through oxygen and hydrogen production. Interpretation of fossil microbial mats and their potential role in alteration of the Earth's geochemical environment is challenging because these mats are generally not well preserved.Preservation of microbial mats in the fossil record can be enhanced through carbonate precipitation, resulting in the formation of lithified mats, or microbialites. Several types of microbially-mediated mineralization can be distinguished, including biologically-induced and biologically influenced mineralization. Biologically-induced mineralization results from the interaction between biological activity and the environment. Biologically-influenced mineralization is defined as passive mineralization of organic matter (biogenic or abiogenic in origin), whose properties influence crystal morphology and composition. We propose to use the term organomineralization sensu lato as an umbrella term encompassing biologically influenced and biologically induced mineralization. Key components of organomineralization sensu lato are the “alkalinity” engine (microbial metabolism and environmental conditions impacting the calcium carbonate saturation index) and an organic matrix comprised of extracellular polymeric substances (EPS), which may provide a template for carbonate nucleation. Here we review the specific role of microbes and the EPS matrix in various mineralization processes and discuss examples of modern aquatic (freshwater, marine and hypersaline) and terrestrial microbialites.
... This amino acid is taken up effectively by Synechocystis sp. PCC 6803 (Montesinos et al., 1997), is the end-product of an alternative CO 2 fixation pathway (Linko et al., 1957; Tabita, 1987 Tabita, , 1994), and might also accumulate at such a concentration intracellularly , when cyanophycin (multi-L-arginyl-poly-Laspartate ) (Simon, 1971Simon, , 1987 Allen, 1984; Kolodny et al., 2006; Maheswaran et al., 2006) becomes degraded. The presence of an L-arginine dehydrogenase as an alternative substrate dehydrogenase sheds new light on the special role of L-arginine in the cyanobacterial metabolism and might contribute to a better understanding of the complex dynamic metabolism of cyanophycin as a N-and also Creservoir (Simon, 1971Simon, , 1987 Allen, 1984 Allen, , 1988 Mackerras et al., 1990a, b; Berg et al., 2000; Maheswaran et al., 2006) and of the complex interrelationship of L-arginine catabolism with photosynthesis/ respiration (Schriek 2008, Schriek et al., 2007, Stephan et al.., 2000) Our model (Fig. 7) implies that under conditions, under which the L-arginine concentration reaches a threshold level, L-arginine via Slr0782 and water via PSII are alternative electron donors to the electron transport chain. ...
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Article
The protein Slr0782 from Synechocystis sp. PCC 6803, which has similarity to L-amino acid oxidase from Synechococcus elongatus PCC 6301 and PCC 7942, has been characterized in part. Immunoblot blot analysis showed that Slr0782 is mainly thylakoid membrane-associated. Moreover, expression of slr0782 mRNA and Slr0782 protein were analyzed and an activity assay was developed. Utilizing toluene-permeabilized cells, an L-arginine-stimulated O2 uptake became detectable in Synechocystis sp. PCC 6803. Besides oxidizing the basic L-amino acids L-arginine, L-lysine, L-ornithine, and L-histidine, a number of other L-amino acids were also substrates, while D-amino acids were not. The best substrate was L-cysteine, and the second best was L-arginine. The L-arginine-stimulated O2 uptake was inhibited by cations. The inhibition by o-phenanthroline and salicylhydroxamic acid suggested the presence of a transition metal besides FAD in the enzyme. Moreover, it is shown that inhibitors of the respiratory electron transport chain, such as KCN and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, also inhibited the L-arginine-stimulated O2 uptake, suggesting that Slr0782 functions as an L-arginine dehydrogenase, mediating electron transfer from L-arginine into the respiratory electron transport chain utilizing O2 as electron acceptor via cytochrome oxidase. The results imply that Slr0782 is an additional substrate dehydrogenase being able to interact with the electron transport chain of the thylakoid membrane.
... The deduced amino acid sequence of the Haloarcula gap gene product shares roughly 50~o identical residues with GAPDH proteins from eubacteria and eukaryotes, but like eubacterial GAPDH, it shares only ca. 15~o identical residues with sequences from methanogenic archaebacteria[19]suggesting that, in analogy to class I and class II aldolases[36], type I and type II glutamine syntheases[27], or form I and form II Rubisco[7,33,47], archaebacteria may possess 'class I' and 'class II' GAPDH (manuscript in preparation). Downstream of the gap gene we found a 1203 bp open reading frame, the predicted product of which (Fig. 1) shows ~ 3 7 ~ identity to PGK from methanogenic archaebacteria and < 30~o identity to PGK from eukaryotes and eubacteria. ...
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Article
Previous studies indicated that plant nuclear genes for chloroplast and cytosolic isoenzymes of 3-phosphoglycerate kinase (PGK) arose through recombination between a preexisting gene of the eukaryotic host nucleus for the cytosolic enzyme and an endosymbiont-derived gene for the chloroplast enzyme. We readdressed the evolution of eukaryotic pgk genes through isolation and characterisation of a pgk gene from the extreme halophilic, photosynthetic archaebacterium Haloarcula vallismortis and analysis of PGK sequences from the three urkingdoms. A very high calculated net negative charge of 63 for PGK from H. vallismortis was found which is suggested to result from selection for enzyme solubility in this extremely halophilic cytosol. We refute the recombination hypothesis proposed for the origin of plant PGK isoenzymes. The data indicate that the ancestral gene from which contemporary homologues for the Calvin cycle/glycolytic isoenzymes in higher plants derive was acquired by the nucleus from (endosymbiotic) eubacteria. Gene duplication subsequent to separation of Chlamydomonas and land plant lineages gave rise to the contemporary genes for chloroplast and cytosolic PGK isoenzymes in higher plants, and resulted in replacement of the preexisting gene for PGK of the eukaryotic cytosol. Evidence suggesting a eubacterial origin of plant genes for PGK via endosymbiotic gene replacement indicates that plant nuclear genomes are more highly chimaeric, i.e. contain more genes of eubacterial origin, than is generally assumed.
Article
The enigmatic coexistence of O2-sensitive nitrogenase and O2-evolving photosynthesis in diazotrophic cyanobacteria has fascinated researchers for over two decades. Research efforts in the past 10 years have revealed a range of O2 sensitivity of nitrogenase in different strains of cyanobacteria and a variety of adaptations for the protection of nitrogenase from damage by both atmospheric and photosynthetic sources of O2. The most complex and apparently most efficient mechanisms for the protection of nitrogenase are incorporated in the heterocysts, the N2-fixing cells of cyanobacteria. Genetic studies indicate that the controls of heterocyst development and nitrogenase synthesis are closely interrelated and that the expression of N2 fixation (nif) genes is regulated by pO2.
Chapter
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 of carbon, cyanobacteria have become important tools for gaining an understanding of the biochemical and molecular mechanisms involved. These organisms take on added significance because the entire process, the catalysts employed and their structural genes, are to some extent quite similar to those of higher plants. Because of the relative ease in using molecular techniques and transferring genetic information in cyanobacteria, there are many advantages to these organisms as models for green plant CO2 metabolism. There are also differences that make cyanobacteria fascinating in their own right. Over the last few years, there has been a tremendous upsurge in interest in cyanobacterial CO2 fixation research. Important insights relative to the biochemistry of the process have emerged, fueled by the revolution in molecular biology. This chapter thus considers the current state of the field and reviews the many important contributions that have been made on this interesting and important area of cyanobacterial research.
Chapter
At present we have considerable knowledge of the pathways of carbon and nitrogen metabolism in photosynthetic microorganisms, although relatively little is known about the precise biochemical mechanisms involved in their regulation or the interrelationships between them (see Smith 1982; Lara et al. 1987; Turpin et al. 1988). In this paper we consider the mechanisms by which the enzyme glucose-6-phosphate dehydrogenase (G6PDH) of cyanobacteria is regulated. The oxidative pentose phosphate (OPP) pathway, is the main route of fixed carbon dissimilation in cyanobacteria and it is considered that metabolic control is exerted at the first step of the pathway, catalyzed by G6PDH (Pelroy and Bassham 1972; Pelroy et al. 1972).
Chapter
Cyanobacteria are photosynthetic prokaryotes that mainly use CO2 and bicarbonate as carbon sources, and ammonium and nitrate as nitrogen sources to fulfil their requirement for growth. Some strains can also fix molecular N2 either under aerobic or anaerobic conditions16,27. Under autotrophic conditions, the enzymatic reactions required for the utilization of any form of inorganic nitrogen depend upon the availability of energy (ATP) and reductant generated from photosynthesis, as well as upon CO2-fixation products, which in part act as amino acceptors to generate amino acids and other organic nitrogenous compounds. There might thus exist tight interactions between nitrogen and carbon metabolism to balance the intracellular N/C ratio.
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Chapter
errestrial carbonates are formed by the combination of calcium and carbonate ions. This combination is related to the biogeodynamics of carbonate solutions at the surface of continents and their crust. Calcium is a ubiquitous element on Earth. The principles of calcium carbonate formation are relatively simple. It combines with carbonate ions and is mainly linked to pH and CO2 activity. Nevertheless, the formation of terrestrial carbonates is not only re- lated to purely physico-chemical reactions. Life plays a major role in their formation on the surface of the conti- nents. The main living contributors to calcium carbonate precipitation are micro-organisms such as bacteria, fungi and algae. Plants also contribute to the formation of specific facies such as nodules, rhizoconcretions or cyto- morphous pseudo-sands. Plants are major contributors to carbonate pedogenesis. Terrestrial carbonate environments are extremely diverse: hilly interfliwes and pediment areas, lakes and marshes, travertines and carbonate dunes are only a few examples. Terrestrial carbonates form many different sedimentary facies. Calcitic cements, pedogenic and organic features are used to study the paleo-conditions of facies formation. The petrology of terrestrial carbonates is often complex but enables various steps to be reconstructed which have led to the carbonate sediment diagenesis. Terrestrial carbonates are excellent tools for paleogeographic investigations because of their ability to record all the fluctuations of their environment.
Article
A daily rhythm of microbial processes, in terms of sub-mm order lamination, was identified for a microbe-rich aragonite travertine formed at a low-flow site of the Nagano-yu Hot Spring in Southwestern Japan. Continuous observation and sampling clearly showed that the lamination consisted of diurnal microbe-rich layers (M-layers) and nocturnal crystalline layers (C-layers). The M-layers originated from biofilm formed by growth and upward migration of filamentous cyanobacteria related to Microcoleus sp., which can rapidly glide and secrete extracellular polymeric substances (EPS). During the daytime, cyanobacterial biofilm development inhibited aragonite precipitation on the travertine surface due to the calcium-binding ability of EPS. After sunset, aragonite precipitation started on the surface where aerobic heterotrophic bacteria decomposed EPS, which induced precipitation of micritic crystals. This early stage of C-layer formation was followed by abiotic precipitation of fan-shaped aragonite aggregates. Despite their major role in lamina formation, the cyanobacteria were readily degraded within 6–10 days after embedding, and the remaining open spaces in the M-layers were sparsely filled with crystal clots. These lamina-forming processes were different from those observed in a high-flow site where the travertine has a dense texture of aragonite crystals. The microbial travertine at Nagano-yu is similar to some Precambrian stromatolites in terms of in situ mineral precipitation, regular sub-mm order lamination, and arrangement of filamentous microbes; therefore, the lamination of these stromatolites possibly occur with a daily rhythm. The microbial processes demonstrated in this study may revise the interpretation of ancient stromatolite formation.
Article
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 tools for gaining an understanding ofthe biochemical and molecular mechanisms involved. These organisms take on added significance because the entire process, the catalysts employed and their structural genes, are to some extent quite similar to those of higher plants. Because of the relative ease in using molecular techniques and transferring genetic information in cyanobacteria, there are many advantages to these organisms as models for green plant CO2 metabolism. There are also differences that make cyanobacteria fascinating in their own right. Over the last fewyears, there has been a tremendous upsurge in interest in Cyanobacterial CO2 fixation research. Important insights relative to the biochemistry of the process have emerged, fueled by the revolution in molecular biology. This chapter thus considers the current state of the field and reviews the many important contributions that have been made on this interesting and important area of cyanobacterial research.
Article
Growth, morphological, biochemical and physiological characteristics of cyanobacteria are influenced by adaptation to different light and CO2 conditions. Despite the individual features of every cyanobacterial strain, several common adaptation mechanisms are understood. The primary photosynthetic apparatus of most cyanobacteria comprises five functional protein complexes: phycobilisomes, photosystem I (PS I), photosystem II (PS II), plastoquinone-plastocyanin oxidoreductase and ATP synthase. The carbon utilization apparatus is closely related in function and it contains carbonic anhydrase(s) and ribulose-bisphosphate carboxylase/oxygenase integrated in carboxysomes.
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A biogeochemical traverse is presented for a juvenile benthic mat covering the depth profile of an artificially stratified and eutrophicated hypersaline heliothermal pond with known gradients of temperature, salinity, pH, and light transmission. It can be shown that visual mat development depends primarily on temperature and salinity as main environmental steering variables whose increase with depth goes along with the attenuation and final disappearance of a visible microbial film in the pond's hypolimnic compartment. Recorded biogeochemical parameters (Corg content, cell numbers, chlorophyll-a content) evidently reflect, as either biomass- or productivity-related index functions, the visually perceptible growth gradient of the microbial ecosystem along the pond slope. The observed coincidence of maxima in these index functions with maxima in δ13Corg clearly identifies high rates of primary productivity as the agent ultimately responsible for the generation of isotopically heavy (13C-enriched) biomass in these and related environments. Extreme demands placed on the local feeder pool of dissolved inorganic carbon by high rates of primary productivity entertained by the mat-forming microbenthos obviously give rise to severe CO2 limitation, enforcing the operation of a diffusion-(supply-)limited assimilatory pathway with an isotopically indiscriminate metabolization of the available CO2 resources.
Article
Growth, morphological, biochemical and physiological characteristics of cyanobacteria are influenced by adaptation to different light and CO2 conditions. Despite the individual features of every cyanobacterial strain, several common adaptation mechanisms are understood. The primary photosynthetic apparatus of most cyanobacteria comprises five functional protein complexes: phycobilisomes, photosystem I (PS I), photosystem II (PS II), plastoquinone-plastocyanin oxidoreductase and ATP synthase. The carbon utilization apparatus is closely related in function and it contains carbonic anhydrase(s) and ribulose-bisphosphate carboxylase/oxygenase integrated in carboxysomes.Phycobilisomes function as light-harvesting antennae, exhibiting a high sensitivity to alterations on light and CO2. Their remarkable response to environmental factors consists in variations of size and/or biliprotein compositions, adaptations of the core influencing the energy sharing, and in alterations of the number of phycobilisomes per cell. This amount of phycobilisomes is strongly related to the number of PS II core particles. Consequently their variation means a differentiation of the PS II:PS I ratio. The ratio of PS II/PS I is also changed by an increase or decrease of PS I. It is suggested that these alterations depend on the redox state of the electron transport chain. Additional to the photosystem core complexes (PS I/PS II), light-harvesting and/or protecting chlorophyll-and caroteno-proteins are differentiated. They generally accumulate in the cells at stress conditions. The carbon-concentrating mechanism of cyanobacteria reacts to supplements of CO2, HCO−3 or general deprivation of both by changing the activity of the carbonic anhydrase(s) and/or by the amount of carboxysomes. Photosynthetic and carbon utilization apparatus are correlated which is demonstrated by the adaptation of phycobilisomes, PS I/ PS II ratios, carotenoid content and carbonic anhydrase(s) activity as well as all other physiological data.
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Dating from the Pre-Cambrian era, cyanobacteria have a long history of adaptation to the Earth's environment. By evolving oxygen via photosynthetic reactions similar to those of plants and green algae, these prokaryotes were essential to the evolution of the present biosphere. They continue to make a large contribution to the equilibrium of the Earth's atmosphere by production oxygen and removing carbon dioxide. To survive in extreme or variable environments, cyanobacteria have developed specific regulatory systems, in addition to more general mechanisms equivalent to those of other prokaryotes or photosynthesis eukaryotes. Specific regulatory systems control the differentiation of specialized nitrogen-fixing cells and of cell types facilitating the dispersion of species. In the past decade, considerable progress has been made towards understanding the expression of the cyanobacterial genome in response to variations in the intensity and spectral quality of incident light and in response to nutritional conditions, especially carbon, nitrogen and sulphur sources. These studies have provided insights into the relationships between carbon and nitrogen intermediary metabolism, and a start towards understanding of the interconnected pathways which lead from the perception of environmental signals to the regulation of enzyme activities and gene expression. Cyanobacterial regulatory mechanisms share common features with those of other prokaryotes, but are unique since these essentially photo-autotrophic organisms must maintain a proper cellular C/N balance, in spite of dailty variations in incident light. Thus an appropriate coordination between photosynthesis and other metabolic processes must be achieved through control of the catalytic activity of key enzymes by reducing equivalents and ATP produced by photosynthetic or respiratory electron transport. Recently discovered kinases/phosphatases act by post-translational modification of specific proteins which probably act as signal transducers or modulators of gene expression in a manner similar to the well-known two-component regulatory systems described in other bacteria. In this overview, we present our current knowledge on the molecular aspects of the biology of cyanobacteria, as well as on their mechanisms of resistance to metal ions and their responses to metabolic stress.
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Rhodobacter sphaeroides was found to contain two clusters of chromosomally encoded CO2 fixation structural genes. Recent studies indicate that genes within each cluster are cotranscribed, suggesting that there is a single long transcript for each cluster. All of the genes have been sequenced, homologies noted, specific mutations obtained, and interesting upstream regulatory sequences found. Site-directed mutagenesis studies of the Anacystis rbcS has begun to provide information relative to RubisCO structure and function. In addition, RubisCO-negative strains of photosynthetic bacteria have been constructed to screen for altered RubisCO sequences.
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Heterocysts of free-living cyanobacteria lack ribulose-1,5-bisphosphate carboxylase activity. Nevertheless, using in situ hybridizations, we demonstrate that transcripts for the rbcL and rbcS genes are present in both heterocysts and vegetative cells of Anabaena spp. in association with, or isolated from, the Azolla-Anabaena symbiosis. In contrast, rbcLS transcripts were detected only in vegetative cells of the free-living cyanobacterium Anabaena strain 7120. Under anaerobic growth conditions that inhibited heterocyst differentiation, transcripts for nitrogenase were present in all cells composing Anabaena strain 7120 filaments, whereas rbcL and rbcS transcripts were not detected. Thus, transcriptional regulation of genes related to photosynthesis and nitrogen fixation is under environmental, as well as developmental, control in Anabaena spp. In addition, these results suggest either the possible retention of regulatory patterns in symbiotically derived cyanobacterial isolates or differences in expression of rbcLS genes in different free-living cyanobacteria.
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The involvement of a gene of Synechocystis PCC6803, icfG, in the co-ordinated regulation of inorganic carbon and glucose metabolism, was established. The icfG gene codes for a 72 kDa protein, which shows no homology with those registered in data libraries. Expression of icfG required glucose, the actual inducer probably being glucose-6-phosphate, and was independent of light and of the external inorganic carbon concentration. Mutants carrying an inactivated copy of icfG were constructed. Their growth characteristics were identical to those of the wild type under all regimes except in limiting inorganic carbon with glucose being present either before or after the transfer to the limiting conditions. These conditions completely prevented growth, both in the light and in the dark. The inhibition could be relieved by several intermediates of the tricarboxylic acid cycle. Assays of various enzymic activities related to inorganic carbon uptake and to its assimilation via either the Calvin cycle or phosphoenolpyruvate carboxylase did not reveal the level of action of IcfG. Possible models include a blockage of the assimilation of both carbon sources in the absence of IcfG, or the inhibition of Ci incorporation route(s) essential under limiting inorganic carbon conditions, even when glucose is present, and even in the dark.
Article
A gene encoding ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (rca) was found downstream from the rbcLrbcS operon in the heterocystous cyanobacterium Anabaena sp. strain CA. Two unknown open reading frames were shown to be located between rbcS and rca in strain CA and all the genes, rbcLrbcS, ORF1, ORF2, and rca were in the same transcriptional orientation. The deduced amino acid sequence of the Anabaena Rubisco activase showed both similarities and differences to the plant enzyme with considerable differences at the carboxy and amino termini. Proposed ATP-binding sites were conserved in the cyanobacterial protein. Recombinant cyanobacterial Rubisco activase, however, reacted with antisera to spinach Rubisco activase. Hybridization studies, using the Anabaena sp. strain CA rca gene as a heterologous probe, detected homologous sequences in heterocystous Anabaena/Nostoc strains but not in unicellular or nonheterocystous filamentous cyanobacteria, suggestive of a close evolutionary relationship of chloroplasts and heterocystous cyanobacteria.
Article
The gene (aoxA) coding for an L-amino acid oxidase (L-AOX) with high specificity for basic L-amino acids (L-arginine being the best substrate) in the cyanobacterium Synechococcus PCC 6301 has previously been identified, sequenced and analysed (Bockholt, R., Masepohl, M., Kruft, V., Wittmann-Liebold, B. and Pistorius, E.K. (1995) Biochim. Biophys. Acta 1264, 289-293). Here we report on the inactivation of the aoxA gene in the closely related Synechococcus PCC 7942 by interrupting the gene with a kanamycin resistance cassette from Tn5. The mutant called D6 has no detectable L-AOX activity and no detectable L-AOX protein. Characterization of the mutant showed that in contrast to Synechococcus PCC 7942 wild-type (WT) cells the mutant cells can not grow on L-arginine as sole N-source, suggesting that the L-AOX is essential for growth on L-arginine. Mutant cells can grow on nitrate or ammonium as N-source under photoautotropic conditions with a growth rate of about 75% of the WT rate. Under these conditions the photosynthetic O2 evolving activity is reduced by about the same amount, and the pigment content, especially the phycobiliprotein content, is much lower than in WT cells, indicating that the mutant suffers from some type of deficiency. Immunocytochemical investigations and extraction of the soluble proteins from periplasma after plasmolysing the cell wall gave evidence that the L-AOX is predominantly located in the periplasma with only a small amount being intracellularly located. A model of the possible function of the L-AOX in Synechococcus PCC 6301/7942 will be given.
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