High recovery of nitrogenase activity and of Fe-labeled nitrogenase in heterocysts isolated from Anabaena variabilis

5-Aminolevulinate Synthesis in Permeabilized Filaments of the Blue-Green Alga Anabaena variabilis

Filaments of the blue-green alga Anabaena variabilis permeabilized by dimethylsulfoxide (DMSO) produce increased amounts of 5-aminolevulinate in the presence of levulinic acid. The metabolic activity of the filaments remains unperturbed in the presence of up to 7.5% (v/v) DMSO. Studies utilizing DMSO-permeabilized filaments confirm that 5-aminolevulinate is synthesized preferably from glutamate and, to a lesser extent, from alpha-ketoglutarate in this organism.

Feasibility of 55 Fe Autoradiography as Performed on N 2 -Fixing Anabaena spp. Populations and Associated Bacteria

55 Fe emits low-energy X rays and Auger electrons by electron capture decay. Auger electrons are useful for autoradiographic examination of 55 Fe incorporation among microbial communities. Attainable resolution, in terms of silver grain deposition, is excellent and comparable to 3 H. Two known Fe-demanding processes, photosynthetic CO 2 fixation and N 2 fixation, were examined by autoradiography of Anabaena populations. During photosynthetically active (illuminated) N 2 -fixing periods, biological incorporation of 55 FeCl 3 by vegetative cells and heterocysts was evident. When N 2 fixation was suppressed by NH 4 + additions, heterocysts revealed no incorporation of 55 Fe. Conversely, when N 2 -fixing Anabaena filaments were placed in darkness, 55 Fe incorporation decreased in vegetative cells, whereas heterocysts showed sustained rates of 55 Fe incorporation. Bacteria actively incorporated 55 Fe under both light and dark conditions. The chelated (by Na 2 -ethylenediaminetetraacetate) form of 55 FeCl 3 was more readily incorporated than the nonchelated form. Furthermore, abiotic adsorption of 55 Fe to filters and nonliving particles proved lower when chelated 55 Fe was used in experiments. 55 Fe autoradiography is useful for observing the fate and cellular distribution of various forms of Fe among aquatic microbial communities.

Light and dark reactions of the uptake hydrogenase in anabaena 7120

Reactions of the uptake hydrogenase from Anabaena 7120 (A.T.C.C. 27893, Nostoc muscorum) were examined in whole filaments, isolated heterocysts, and membrane particles. Whole filaments or isolated heterocysts that contained nitrogenase consumed H(2) in the presence of C(2)H(2) or N(2) in a light-dependent reaction. If nitrogenase was inactivated by O(2) shock, filaments catalyzed H(2) uptake to an unidentified endogenous acceptor in the light. Addition of NO(3) (-) or NO(2) (-) enhanced these rates. Isolated heterocysts consumed H(2) in the dark in the presence of electron acceptors with positive midpoint potentials, and these reactions were not enhanced by light. With acceptors of negative midpoint potential, significant light enhancement of H(2) uptake occurred. Maximum rates of light-dependent uptake were approximately 25% of the maximum dark rates observed. Membrane particles prepared from isolated heterocysts showed similar specificity for electron acceptors. These particles catalyzed a cyanide-sensitive oxyhydrogen reaction that was inactivated by O(2) at O(2) concentrations above 2%. Light-dependent H(2) uptake to low potential acceptors by these particles was inhibited by dibromothymoquinone but was insensitive to cyanide. In the presence of O(2), light-dependent H(2) uptake occurred simultaneously with the oxyhydrogen reaction. The pH optima for both types of H(2) uptake were near 7.0. These results further clarify the role of uptake hydrogenase in donating electrons to both the photosynthetic and respiratory electron transport chains of Anabaena.

Metabolism of sulfur compounds by whole filaments and heterocysts of Anabaena variabilis

Filaments of the heterocyst-forming cyanobacterium Anabaena variabilis reproduced 35SO4(2)-, incorporating 35S into cysteine, methionine, glutathione, sulfolipid, and several unidentified metabolites. The majority of the incorporated label accumulated in reduced glutathione. Heterocysts isolated from labeled filaments contained the same major labeled products. Isolated, metabolically active heterocysts were unable to reduce 35SO4(2)-, but were able to incorporate 35S2- into cysteine and glutathione. The results suggest that the initial activation of SO4(2)- occurs in vegetative cells and that some reduced forms, possibly including S20, are translocated into heterocysts.

Comparative characterization of two distinct hydrogenases from Anabaena sp. strain 7120

Two distinct hydrogenases, hereafter referred to as "uptake" and "reversible" hydrogenase, were extracted from Anabaena sp. strain 7120 and partially purified. The properties of the two enzymes were compared in cell-free extracts. Uptake hydrogenase was largely particulate, and although membrane bound, it could catalyze an oxyhydrogen reaction. Particulate and solubilized uptake hydrogenase could catalyze H2 uptake with a variety of artificial electron acceptors which had midpoint potentials above 0 mV. Reversible hydrogenase was soluble, could donate electrons rapidly to electron acceptors of both positive and negative midpoint potential, and could evolve H2 rapidly when provided with reduced methyl viologen. Uptake hydrogenase was irreversibly inactivated by O2, whereas reversible hydrogenase was reversibly inactivated and could be reactivated by exposure to dithionite or H2. Reversible hydrogenase was stable to heating at 70 degrees C, but uptake hydrogenase was inactivated with a half-life of 12 min at this temperature. Uptake hydrogenase was eluted from Sephadex G-200 in a single peak of molecular weight 56,000, whereas reversible hydrogenase was eluted in two peaks with molecular weights of 165,000 and 113,000. CO was competitive with H2 for each enzyme; the Ki's for CO were 0.0095 atm for reversible hydrogenase and 0.039 atm for uptake hydrogenase. The pH optima for H2 evolution and H2 uptake by reversible hydrogenase were 6 and 9, respectively. Uptake hydrogenase existed in two forms with pH optima of 6 and 8.5. Both enzymes had very low Km's for H2, and neither was inhibited by C2H2.

The developmental biology of heterocyst and akinete formation in cyanobacteria

We will be concerned with the two major differentiated cell types of filamentous cyanobacteria--the heterocyst and the akinete. The former is generally accepted to be the site of aerobic nitrogen fixation in heterocystous cyanobacteria. The latter is a spore-like cell capable of withstanding certain environmental extremes and of germination. A short general introduction to cyanobacteria and their cell types will be included. The remainder of the review will fall into four main sections. The first will deal with the metabolism of the heterocyst and akinete, with particular reference to nitrogen fixation in the former. The next will be concerned with a description of the metabolic and ultrastructural changes associated with heterocyst and a kinete development. A third section will describe the special arrangement of the heterocyst and akinete (one of the features which makes this group of prokaryotes unique), the relationship between the cell types, and methods of altering this normal regular spatial pattern. The final section will describe in detail present theories of pattern control in cyanobacteria and the mechanisms by which the process of differentiation itself is regulated.

Control of phycobiliprotein proteolysis and heterocyst differentiation in Anabaena

Phycobiliprotein degradation can be initiated in cultures of the cyanobacterium Anabaena by removal of combined nitrogen from the medium. Certain strains of Anabaena differentiate cells specialized for aerobic nitrogen fixation (heterocysts) under such conditions. We describe here a procedure for the preparation of extracts from heterocysts or vegetative cells that contain an activity capable of degrading only the phycobiliproteins in a mixture of soluble Anabaena proteins in vitro. This activity increased under nitrogen starvation conditions or in ammonia-replete cultures treated with the glutamine synthetase inhibitor methionine sulfoximine. The increase in activity induced by nitrogen starvation was prevented by chloramphenicol or by carbon starvation. Under all these conditions, phycobiliprotein degradative activity assayed in vitro was correlated with the loss of phycobiliprotein absorbance in vivo. Finally, starvation of a met auxotroph of Anabaena for methionine (in the presence of ammonia) did not induce phycobiliprotein degradation in vivo or the increase in proteinase activity. Together with direct measurements of ppGpp, these results indicate that proteolysis in Anabaena is not controlled by compounds associated with the stringent response in Escherichia coli. Since the increase in proteinase activity appears to be regulated by the same variables that control heterocyst differentiation, the activity should provide a useful biochemical marker for the early events of differentiation.