ISSN:0008-4026    

DOI:10.1139/b91-117

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

CO2-concentrating mechanisms based on active inorganic C influx across a membrane (or membranes) are widespread in aquatic phototrophs. They are apparently absent from, or poorly developed in, taxa such as bryophytes and freshwater red algae, but are retained in some terrestrial phototrophs, i.e., some lichens and free-living algae and cyanobacteria related to the lichen photobionts. The natural occurrence of CO2-concentrating mechanisms is negatively correlated with CO2enrichment of aquatic habitats from respiration of organic C produced elsewhere and, less clearly, with low temperatures during the growing season, with low external pH, and with rapid water movement over the plant surface. Predictions based on laboratory data and on theoretical considerations as to the influence of light, nitrogen, and iron availability on the occurrence of CO2-concentrating mechanisms have yet to be rigorously tested in the field. The evolution of CO2-concentrating mechanisms is not well understood, but clearly the location of inorganic C pumps must have been influenced by successive symbiotic events. Increasing atmospheric CO2levels, and other anthropogenic effects (acidification, eutrophication), may influence the selective advantage (or disadvantage) associated with possession of CO2-concentrating mechanisms in particular environments.Key words: bicarbonate, CO2-concentrating mechanisms, iron, light, nitrogen, unstirred layers.

ISSN:0008-4026    

DOI:10.1139/b91-118

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Cyanobacteria appear to possess an active transport system for molecular CO2. This system, first discovered by Badger and Andrews in 1982 (1982. Plant Physiol. 70: 517–523), is without reported precedence in the bacterial, animal, or plant literature. The transport system operates so efficiently that in dense cell suspensions the extracellular CO2concentration is pulled far below the equilibrium value. This CO2drawdown is not due to CO2fixation but can be accounted for by a transport system that recognizes molecular CO2and causes it to be transported into the cell. The fact that operation of the system causes a massive disequilibration of the extracellular CO2–HCO3−system means that there must be an expenditure of metabolic energy. The CO2is actually moved against a considerable CO2concentration gradient. In this review we discuss methods that can be used to monitor CO2transport in cyanobacteria. We present evidence that CO2transport is an active process. It is emphasized that little is known about the concomitant ion fluxes that must occur to ensure charge and pH regulation during CO2transport.Key words: cyanobacteria, active CO2transport, metabolic inhibitors, transport models.

ISSN:0008-4026    

DOI:10.1139/b91-119

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Cyanobacteria possess systems for the active transport of both CO2and HCO3−. While the active CO2transport system seems to be present in cells grown on all levels of CO2or dissolved inorganic carbon, the bicarbonate transport systems are only present in cells grown on low levels of CO2or dissolved inorganic carbon (air levels or lower). Active bicarbonate transport can be shown to occur when the rate of photosynthesis exceeds that which could be sustained by the production of CO2from the dehydration of bicarbonate or when CO2transport is inhibited with carbon oxysulfide or hydrogen sulfide. Two systems for active bicarbonate transport have been identified: one is dependent on the presence of millimolar concentrations of sodium, and the other is independent of the sodium requirement. Cells grown with air bubbling normally possess the first whereas cells grown in standing culture normally possess the second. The sodium-dependent bicarbonate transport can be inhibited by omitting sodium from the reaction medium or competitively with lithium when sodium is present. Monensin and amiloride also inhibit sodium-dependent bicarbonate transport. It does not appear to be inhibited by ethoxyzolamide. The inhibition of sodium-independent bicarbonate transport is not yet established. Bicarbonate transport appears to have no effect on CO2transport and CO2transport appears to have no effect on bicarbonate transport. Hence, the transport systems seems to be independent. Although a number of mechanisms have been proposed for bicarbonate transport, the experimental data are not sufficient to clearly distinguish between them.Key words: cyanobacteria, active CO2transport, active HCO3−transport, photosynthesis, sodium.

ISSN:0008-4026    

DOI:10.1139/b91-120

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Modifications of the genomic region near (and including)rbc, the operon that codes for the large and small subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), resulted in cyanobacterial mutants that demand high CO2for growth. Mutant EK6 originated from the fusion of the 3' end ofrbcS(which codes for the small subunit of Rubisco) with 84 nucleotides from the 5′ flanking region ofnptII(kanamycin-resistance gene), leading to a 17-kDa small subunit, as compared to 14 kDa in the wild type. Mutant D4 originated from substitution of the 1.4-kbPstI fragment, downstream ofrbc, withnptII, inactivating several open reading frames in this region. Mutant O105 was obtained by chemical mutagenesis and the mutation was mapped approximately 9 kb upstream ofrbc. Mutants EK6 and O105 exhibited a very low apparent photosynthetic affinity for inorganic carbon, whereas D4 had an affinity similar to that observed in wild-type cells grown under high CO2. These mutants, and the constructs used to raise them, can be used to study the role of the small subunit of Rubisco and the genomic region nearrbcin cyanobacterial photosynthesis. We propose that this region contains a cluster of genes involved in the ability of cyanobacteria to grow under low ambient CO2..

ISSN:0008-4026    

DOI:10.1139/b91-121

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Transformation of the high CO2-requiring mutants ofSynechocystisPCC6803 defective in inorganic carbon (Ci) transport (RKa and RKb) by wild type (WT) DNA libraries restored their ability to grow under air levels of CO2. Two clones (PK-1 and HP-1), which complement RKa and RKb, respectively, were isolated from the libraries. PK-1 contained an 11.8-kilobase pair (kbp) DNA insert. The sequence of amino acid coded in the DNA in the region of the mutation showed an extensive homology to that of thendh2 gene product of liverwort chloroplasts, which is suspected to be the subunit 2 of NADH dehydrogenase. Based on the result, we designated the gene mutated in RKa asndh2. Inactivation of thendh2 gene in the WT cells by inserting an aminoglycoside-3′-phosphotransferase gene generated a mutant (M57) that was unable to grow under low CO2conditions. HP-1 contained a 5.4-kbp DNA insert. Sequencing of nucleotides in the region of the mutation revealed an open reading frame that codes a hydrophobic protein that consists of 80 amino acids. Insertional inactivation of this putative Citransport gene, designatedictA, generated a high CO2-requiring mutant (M9). All these mutants (RKa, RKb, M9, and M57) showed very low activity of CO2uptake into the intracellular Cipools. The activity of HCO3−uptake was negligibly low in RKb, M9, M57 and high CO2-grown cells of RKa, and was about 10% the activity of wild type cells in low CO2-adapted cells of RKa.Key words: CO2-concentrating mechanism, inorganic carbon transport,SynechocystisPCC6803, mutant, NADH dehydrogenase, insertional inactivation.

ISSN:0008-4026    

DOI:10.1139/b91-122

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Since first being isolated and named carboxysomes more than 17 years ago, these prokaryotic inclusions have been studied with great interest. Several summary statements can be made regarding the structure, composition, and function of carboxysomes. The carboxysome is composed of 7–15 peptides, of which 3–5 are shell glycoproteins. The only enzyme demonstrated to be associated with the carboxysomes is ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The carboxysome may be a dodecahedron or an icosahedron. The molecular weight of the carboxysomes fromThiobacillus neapolitanusis approximately 2.4 × 108. Rubisco may fill the carboxysome or line the inner surface of the shell. The carboxysome is active in CO2fixation. The function of the carboxysome is related to the availability of CO2to the cells. The molecular mechanisms of carboxysome function are not yet available.Key words: carboxysomes, review, ribulose-1,5-bisphosphate carboxylase/oxygenase, Rubisco, structure, composition.

ISSN:0008-4026    

DOI:10.1139/b91-123

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

In this paper we provide a brief summary of recent work that supports the notion that the carboxysome, a polyhedral body containing Rubisco, plays a pivotal role in the cyanobacterial CO2-concentrating mechanism. This work includes (i) experiments in which active human carbonic anhydrase II was expressed in the cytosol of the cyanobacteriumSynechococcusPCC7942 resulting in a high CO2-requiring phenotype, and (iii) characterization of two types of high CO2requiring mutants ofSynechococcusthat appear to be incapable of generating CO2within the carboxysomes. Carboxysomes appear to serve as a microcompartment where CO2can be generated and elevated at the site of carboxylation. We also report on the identification by complementation and sequence analysis of a 300 base pair open reading frame that is located upstream ofrbcLand that is involved in the correct functioning of the carboxysome. Preliminary electron microscopy data is also considered on the biogenesis of carboxysomes inAnabaena variabilisM3.Key words: carboxysome, cyanobacteria, carbonic anhydrase, CO2-concentrating mechanism, genetic analysis, mutants.

ISSN:0008-4026    

DOI:10.1139/b91-124

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The selection and analysis of mutants of the CO2-concentrating mechanism in cyanobacteria have greatly advanced our understanding of the physiological and genetic components of this mechanism. This paper reviews the processes for the creation of mutants and the properties of mutants that have been produced so far. In addition to this, consideration is given to developing new mutant selection protocols, based on our current knowledge of the operation of the CO2-concentrating mechanism. As a result, new screens are suggested for the isolation of transport mutants that are defective in either HCO3−or CO2transport activity, and putative carboxysomal mutants that have altered carbonic anhydrase activities. The procedures for physiological analysis of mutants are also reviewed, with a conclusion that there is a great need for the further development ofin vitroassays, particularly for the inorganic carbon transport process and carboxysome function. Particular consideration is given to thein vitrocarboxysome assay, and it is concluded that many of the properties of a carboxysomal Rubisco may be difficult to resolve owing to increases in carboxysomal leakiness during isolation and the higher ratio of [CO2] to [HCO3−] experienced during assays compared with thein vitrosituation. Finally, consideration is given to the genetic analysis of cyanobacterial mutants and the progress that will need to be made in the future, discovering what are the functions of the proteins coded for by the genes that are isolated.Key words: cyanobacteria, mutants, photosynthesis, carboxysome, CO2-concentrating mechanism.

ISSN:0008-4026    

DOI:10.1139/b91-125

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A barrier to CO2diffusion within the cyanobacterial cell has been regarded as essential for the inorganic carbon concentrating mechanism. We present here an extension of our earlier quantitative model demonstrating that it may be unnecessary to postulate any barrier other than the ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) molecules themselves. It is proposed that carbonic anhydrase is located in the interior of the carboxysome and that the CO2generated is largely fixed as it diffuses outwards past Rubisco sites located along the diffusion path. Equations have been developed, by combining a mass balance equation with Fick's Law and the Michaelis-Menten equation (representing CO2fixation), estimate the value that must be assigned to the diffusion coefficient for CO2within the carboxysome if the CO2concentration is to be reduced to near zero at the carboxysome outer surface. A solution has been obtained for two limiting cases, that where CO2concentration is nearly saturating and that where it is at theKm(CO2) value or below. These two estimates predict that the permeability constant for the Rubisco zone in the carboxysome would have to be 10−2–10−3 cm∙s−1, a value that we suggest is reasonable for three-dimensional diffusion through a densely packed protein layer. The concentration gradient in the inward direction, for substrates penetrating the carboxysomes from the cytoplasm, is shown to be relatively flat, owing to the concentrating effect experienced by solutes passing from the periphery to the center of a sphere.Key words: cyanobacteria, carboxysomes, inorganic carbon fluxes, photosynthesis, mode

ISSN:0008-4026    

DOI:10.1139/b91-126

出版商:NRC Research Press    

年代:1991

数据来源: NRC