Heterocyst structure in Chlorogloea fritschii

Summary Heterocysts of Chlorogloea fritschii were studied with the aid of light and electron microscopy. Two main types of heterocyst were recognized. One of these, termed here the H.1 cell, is the only type in filaments, but occurs also among endospore groups. The other, the H.3 cell, is restricted to endospore groups. The transition from one type of heterocyst to the other, therefore, does not coincide exactly with the transition in arrangement of vegetative cells from filaments to endospores. Both types of heterocyst differ considerably from other published accounts of heterocysts.The differences between H.1 and H.3 cells reside mainly in the arrangement, and relative development or disappearance of the various cell organelles.A summary is given of other types of cell seen with the electron microscope which share some features with typical heterocysts. Some of these would probably be recognized as heterocysts by light microscopy, whereas others would not.     

Properties of the primary electron acceptor complex of photosystem I in the blue green alga Chlorogloea fritschii.

Photooxidation of P700 at low temperatures in membrane fractions from the blue-green alga $\text{Chlorogloea fritschii}$ may be coupled irreversibly to the reduction of a bound ferredoxin. If this ferredoxin is reduced before freezing, P700 photooxidation at low temperatures becomes reversible. This reversible photooxidation is coupled to the reduction of a component with an EPR signal at g = 2.08, 1.88 and 1.78. A complete spectrum of this component has been obtained for the first time. We propose that as in higher plants this component is the primary electron acceptor of Photosystem I, the bound ferredoxin is a secondary electron acceptor. Using ⁵⁷Fe enriched preparations we have shown that the ERP signals attributed to the bound ferredoxin are due to iron containing centres. This experiment did not show the presence of iron in the primary electron acceptor.     

Photosystem 1 preparations from dark-and light-grown cells of the cyanobacterium,Chlorogloea fritschii

Photosystem 1 (PS1) enriched preparations have been extracted from the cyanobacterium Chlorogloea fritschii grown either in darkness or in the light. Absorption spectra show that the main chlorophyll peak has shifted from 678 nm in PS1 from light grown cells to 675 nm in PS1 from dark grown cells. Fluorescence spectra show a similar blue shift in wavelength maximum from 690 nm to 678 nm and the fluorescence intensity is higher in PS1 from dark grown cells. Allophycocyanin is present in PS1 from light grown cells, but absent from preparations from C. fritschii grown in the dark. P700: chlorophyll a ratios of the preparations from light and dark grown cells are 1:35 and 1:80 respectively, all P700 being photoactive. The results are interpreted to suggest that allophycocyanin is not attached to PS1 in dark grown C. fritschii, neither is all chlorophyll arranged in such a way as to ensure efficient energy transfer to P700.     

A requirement for EDTA in the separation of Photosystems 1 and 2 from the cyanobacterium Chlorogloea fritschii.

Fractions enriched in Photosystem 1 or Photosystem 2 activity have been isolated from the cyanobacterium Chlorogloea fritschii after extraction of the membranes with digitonin and Triton X-100. Separation of the extract into the two components was achieved by using a Sepharose 6B column, calibration of which gave Kd values of 0.3 for the Photosystem 1 fraction and 0.53 for Photosystem 2. These values corresponded to molecular weights of approx. 500000 and 90000 respectively. The Photosystem 1 particle was shown to aggregate on storage and EDTA was shown to be necessary to separate the Photosystem 1 and 2 fractions.     

Toxic and inhibitory effects of the blue-green alga Microcystis aeruginosa on herbivorous zooplankton

Blooms of blue-green algae are often associated with declinesin populations of large-bodied cladocerans and increased importanceof small cladocerans, copepods, and rotifers. We conducted toxicityand herbivory experiments, using a wide range of herbivore taxa,to test the hypothesis that the blue-green alga Microcystisaeruginosa most strongly inhibits large cladocerans. For a varietyof herbivore taxa, M. aeruginosa was toxic or non-nutritious,and inhibited feeding on co-occurring nutritious food. The rotiferBrachionus calyciflorus was unique in several respects: it wasunaffected by M. aeruginosa toxins, it showed some ability togrow and reproduce on a diet of M. aeruginosa, and it maintainedhigh feeding rates on co-occurring nutritious food in the presenceof bloom densities of M. aeruginosa. There was a strong relationbetween the toxicity of M. aeruginosa and its inhibitory effecton herbivore feeding rates. Copepods strongly avoided consumingM. aeruginosa, but all cladocerans and rotifers tested filteredunicellular M. aeruginosa at rates similar to or higher thannutritious Chlamydomonas reinhardi. Our results indicate thatthere are a variety of mechanisms whereby herbivorous zooplanktoncan coexist with blooms of M. aeruginosa, including resistanceto toxic chemicals (B. calyciflorus), and avoidance of consumptionof M. aeruginosa by chemosensory means (copepods), or by theinability to consume large colonies (some small cladocerans). ¹Present Address: Department of Biology, George Mason University,4400 University Drive, Fairfax, VA 22030, USA     

Fine structure of developing polyphosphate bodies in a blue-green alga,Plectonema boryanum

Summary Stages in the development of polyphosphate bodies in the blue-green alga, Plectonema boryanum, grown under continuous illumination in the presence of excess phosphate, are reported. During the first stage, an electronlucent area appears near the nucleoplasm or cross walls; it gradually increases to a size approximately equal to that of the final polyphosphate body. In this area a porous structure of medium electron density develops, while simultaneously electron-dense material, interpreted as polyphosphate, is deposited in the adjacent cytoplasm. Eventually, this material seems to penetrate into the porous structure. When the polyphosphate bodies are fully formed, the surrounding cytoplasm does not contain detectable amounts of polyphosphate.The formation of polyphosphate bodies in P. boryanum is compared with that in some bacterial species.     

Mutagenesis of the blue-green alga,Anabaena doliolum Bharadwaja

Mutagenesis in the blue-green alga, Anabaena doliolum Bharadwaja has been investigated with particular reference to N₂ fixation. Several types of mutant have been isolated after induction with UV, NG, acridine orange and acriflavine. From a comparative characterization it is concluded that the heterocyst is not the sole site of N₂ fixation. There does not appear to be a linkage between N₂ fixation and heterocyst or spore differentiation: they seem to be independent processes probably regulated either by different genes or by a single regulatory gene with independent operons. A common genetic determinant has also been suggested for nitrogenase and nitrate and nitrite reductases.     

Fine Structure of Poly-β-Hydroxybutyric Acid Granules in a Blue-Green Alga, Chlorogloea fritschii

Granules characterized as poly-beta-hydroxybutyric acid are described in Chlorogloea fritschii, a blue-green alga. They are generally spherical inclusions of slight electron density which are limited by a membrane approximately 3 nm in thickness.     

Possible toxic effects of the marine blue-green alga, Spirulina subsalsa, on the blue shrimp, Penaeus stylirostris.

Blooms of a marine species of blue-green algae identified as Spirulina subsalsa (Cyanophyta, Oscillatoriacae) were found to be related to a particular disease syndrome in raceway-reared blue shrimp, Penaeus stylirostris. The disease was characterized by necrosis of the lining epithelium of the midgut, dorsal cecum, and hindgut gland, and a consequent hemocytic enteritis. Bacterial infections due predominately to Vibrio alginolyticus were common in affected shrimp and presumed to be a secondary condition resulting from necrosis of the gut epithelium. These bacterial infections were expressed as local abscesses near or on the gut or as fulminating septicemias.     

The effects of ultraviolet irradiation on a coccoid blue-green alga: survival, photosynthesis, and photoreactivation

The effects of UV irradiation (254 mμ) on a coccoid blue-green alga Agmenellum quadruplicatum, Strain PR-6, have been examined in terms of the survival curve and measurement of short time photosynthetic rates. From study of survival evidence has been found for a strong photoreactivation centered near 430 mμ. Measurements of photosynthetic rate suggest that there is a correlation between decay of photosynthesis and survival after UV exposure. The UV induced decay in photosynthetic activity is reversed by the identical photoreactivation conditions that increase the survival level. The photosynthetic data are interpreted as demonstrating a photoreactivation of photosynthesis in blue-green algae.     

Changes in photosynthetic activity in the cyanobacterium Chlorogloea fritschii following transition from dark to light growth.

The cyanobacterium Chlorogloea fritschii loses Photosystem II activity, measured by delayed fluorescence and oxygen evolution, during dark heterotrophic growth, but retains Photosystem I, measured as light induced EPR signals. Following transition to the light, Photosystem II recovers in two stages, the first of which does not require protein synthesis. New Photosystem I reaction centres are not synthesised until after net chlorophyll synthesis has commenced. Carbon dioxide fixation recovery commences immediately, the initial rate being unaffected by chloramphenicol. The recovery of carbon dioxide fixation is not directly related to oxygen evolution rate and is only inhibited slightly by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone.     

Photoorganotrophic growth of a blue-green alga, Anabaena variabilis

By training Anabaena variabilis in the presence of glucose andcasamino acids, the cells became proliferable without a supplyof CO₂. Their growth under these conditions was not affectedby CMU and their growth rates were linearly proportional tothe light intensity, inferring that this growth was independentof photosystem II action and its nutritional mode was of photoorganotrophicnature. The process of transition to this nutritional mode includedat least two consecutive stages: relief from the susceptibilityto organic substances which initially evoked arrest of cellgrowth, followed by the shift of cellular metabolism to organotrophy.In cells grown photoorganotrophically, the contents of phycobilinpigments decreased to nearly one-fifth as much as that of lithotrophicallygrown cells with concomitant degradation of the activity ofphotosynthetic oxygen evolution, while the chlorophyll contentsremained less altered. Accompanying these results, the activityfor incorporating external amino acids into cellular proteinswas enhanced several hundred times. Neither in the dark norin anaerobiosis was this organotrophic growth permitted butwhen light too dim to support lithotrophic growth was supplied,the organotrophic growth was affected at a slow but discerniblerate. (Received August 2, 1974; )     

NADH and NADPH dehydrogenases from the blue-green alga,Aphanocapsa

Two different NAD(P)H dehydrogenases could be demonstrated in the blue-green alga, Aphanocapsa. Both function as quinone reductases using benzoquinone as electron acceptor. One, which was found in the soluble fraction, was NADH specific and showed high sensitivity to rotenone, thenoyltrifluoroacetone and o-phenanthroline. The second dehydrogenase was membrane-bound and used NADH as well as NADPH as substrates. Inhibition by rotenone and o-phenanthroline was less pronounced with the bound enzyme than with the soluble enzyme. Based on studies with NADH or NADPH, the membrane-bound enzyme apparently was associated with a low-temperature EPR signal at g=1.92 in the reduced state, indicative of an iron-sulfur center. The membrane-bound dehydrogenase was solubilized with Triton X-100 and partially purified. This preparation was used for studies of enzyme kinetics and acceptor specificity.Abbreviations DBMIB 2,5-dibromo methyl isopropylbenzoquinone - TTFA thenoyltrifluoroacetone - E_m midpoint redox potential     

Dependence of the photophobic response of the blue-green alga,Phormidium uncinatum,on cations

It is suggested that photophobic responses caused by a sudden step-down in light intensity require the presence of cations in the blue-green alga, Phormidium uncinatum.Drastic removal of cations abolishes the phobic response, which recovers after addition of Ca²⁺ ions. Calcium can be substituted for partially by other cations with an effectivity following the sequence Ca>Mg>Na>Ba>Co=0. During the photophobic response there is a 25% increase in ⁴⁵Ca binding by the cells related to a step-down in light intensity. Three seconds after a light-dark transition there is a sharp increase in the binding of labelled calcium, followed by a subsequent release.Flushing the filaments with high cation concentrations, esp. calcium causes a reversal of movement in the absence of a light stimulus similar to a photophobic reversal. This stimulus could trigger the same sequence of events in the transduction chain bypassing the primary photoresponse.Abbreviations EDTA Ethylene diaminetetraacetic acid - EGTA ethylene glycol-bis (2-aminoethylether) N,N tetraacetic acid     

Accumulation of arsenic in blue-green alga, Phormidium sp

The behavior of a blue-green alga, Phormidium sp., against inorganic arsenic dissolved in media was studied. The Phormidium sp. was shown to have capabilities of endurance against a high concentration stress of arsenic and of accumulation of arsenic. Studies on excretion of arsenic by the alga showed that there were two excretion modes, each of which had a characteristic rate constant and it could be attributed to two types of binding situations between arsenic and the tissues of the alga. The arsenate absorbed by the algae was readily reduced to arsenite within their tissues.     

Die-offs of the blue-green alga,Anabaena variabilis,in fish ponds

Dense populations of the blue-green alga, Anabaena variabilis, frequently develop in fish ponds at Auburn, Alabama, during windy weather in March and early April. Massive die-offs of this alga can be expected when it forms surface scums during prolonged periods of calm, clear, warm weather between mid April and mid May. Dissolved oxygen concentrations decline following die-offs and fish kills may result.