Interrelations of photosynthetic behaviour and buoyancy regulation in a natural population of a blue-green alga

The photosynthetic activity of Anabaena cirdnalis and associated changes in buoyancy were determined from prepared suspensions exposed in the natural light field of Crose Mere. The observations are related to variations in subsurface irradiance and temperature. Parallel experiments, aimed at trapping algal colonies undertaking controlled vertical movements within the lake system, are also described. Buoyancy loss and downward migration are clearly associated with specific photosynthetic rates: rates as low as 1.8 mg O₂ (mg chlorophyll a) h⁻¹ are shown to be sufficient to effect buoyancy loss, while movements in the lake tend towards a depth where rates of 5–7 mg O₂ (mg chlorophyll a)⁻¹ h⁻¹ are possible. These rates are significantly less than those possible at light saturation. The effect of increasing temperature is to depress the population in the light-gradient. The significance of this response is discussed in relation to the growth of natural populations of blue-green algae.     

An investigation into the possible light-shielding role of gas vacuoles in a planktonic blue-green alga

When the gas vacuoles of Anabaena flos-aquae Bréb. ex Born. et Flah. are collapsed, the optical properties of the alga change. While this may suggest a light-shielding role, photosynthetic measurements indicate that intact gas vacuoles reduce the light falling on the thylakoids by only 4%, or less. Intact gas vacuoles offer no protection against the lethal effects of ultraviolet light. When the alga is grown at high light intensity the gas vacuoles are fewer in number but are oriented peripherally in the cells. However, this does not markedly affect their light shielding efficiency. Spectrophotometric measurements carried out by others indicate a light shielding role by gas vacuoles in a non-planktonic blue-green alga, Nostoc muscorum Kütz., but do not give a quantitative estimate of this effect. In Anabaena no definite evidence of light-shielding is obtained by such a method. All of the experiments described were conducted with dilute algal suspensions to investigate shielding effects in individual cells. Possible self-shading effects in dense suspensions and surface water blooms require further investigation.     

Disappearance of gas vacuoles in the blue-green alga Microcystis aeruginosa

Abstract In a culture of Microcystis aeruginosa, which had been transferred from a mineral medium into distilled water, the number of gas vacuoles per cell decreased and reached a value of 20% of the control 24 h after transfer. In senescent cells grown on a mineral agar for several weeks, the gas vacuoles also disappeared. The disappearance of the gas vacuoles may be a response to a nutrient deficiency in both cultures.     

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; )     

Components of natural gas resulting from thermal degradation of the blue-green alga (cyanobacterium)Oscillatoria tenuis

Cultures of the blue-green alga (cyanobacterium)Oscillatoria tenuis were used to simulate thermal degradation and gas formation by heating without oxygen at 250° and 350 °C for 100 h. Analysis through gas chromatography showed that the gases were mainly CH₄, C₂H₆, C₃H₈, iC₄ (isobutane), nC₄ (normal butane), iC₅ (isopentane), nC₅ (normal pentane), H₂, C0₂ and N₂. The volume of gases per g dry weight of alga was 44 ml at 250 °C and 100 ml at 350 °C. Alkane gas comprised only 2.04% of the total at 250 °C and rising to 40.0% at 350 °C. The fraction of C0₂ decreased from 83.3% at 250 °C to 40.0% at 350 °C. The quantity of alkane in the soluble organic matter doubled with rising temperature but the H/C atomic ratio in the ‘kerogen’, insoluble organic matter, decreased sharply. Infrared spectra of the ‘kerogen’ showed that the peak of adipose radical at 2900 cm⁻¹ disappeared gradually with rising temperature, which reflects the gradual break of CH₄ or C₂H₆ from ‘kerogen’. This demonstrates that insoluble organic matter rather than soluble organic matter in blue-green algae are the main sources of the gas alkanes in the process of simulated thermal degradation.     

Ion metabolism in a halophilic blue-green alga,Aphanothece halophytica

The intracellular ion content of the halophilic blue-green alga, Aphanothece halophytica was studied as a function of age, external sodium and external potassium concentration. Intracellular Na⁺ was found to be about 0.38 millimoles/g dry mass. Intracellular K⁺ concentrations were as high as 1 M and varied directly with external salinity. Intracellular Ca⁺⁺ and Mg⁺⁺ were in the range previously reported for fresh water blue-green algae despite their extremely high extracellular concentrations. Average cell size is consistent at room temperature with two exceptions. When the outside K⁺ is lower than 6.5 mM the cells tend to be smaller with less intracellular K⁺ and high Ca⁺⁺. In stationary phase cultures the cells are larger with high intracellular Mg⁺⁺ and low K⁺.     

A study of the strength and stability of gas vesicles isolated from a blue-green alga

Summary Acid phosphatase was studied by means of electron microscope cytochemistry in glutaraldehyde-fixed myxamoebae of Dictyostelium discoideum grown on dead bacteria. The enzyme activity was localized to the digestive vacuoles in vegetative as well as in aggregating cells. Biochemical experiments showed that the enzyme was not inactivated by fixation in 2% purified glutaraldehyde.Abbreviations used NPP p-nitrophenyl phosphate - NP p-nitrophenol - GP -glycerophosphate - glc-6-P glucose-6-phosphate - Pi orthophosphate     

Structures in a blue-green alga resembling prolamellar bodies

Summary Cells ofAnabaena (IUCC 380) from soil-water cultures 106 and 168 days after inoculation were fixed in 2% KMnO₄ and studied by electron microscopy. Thylakoid lattices morphologically similar to prolamellar bodies characteristic of etiolated higher plant chloroplasts were discovered. Prefixation sonication and centrifugation were eliminated as factors producing these lattices in the photosynthetic thylakoid system of these prokaryotic cells. Similar lattices are not seen in young cultures in the log phase of growth cultured under the same temperature and light conditions in the same medium. Factors, other than age, producing these lattices are yet to be determined.     

Site of action of the natural algicide,cyanobacterin, in the blue-green alga,Synechococcus sp.

Cyanobacterin is a secondary metabolite produced by the cyanobacterium, Scytonema hofmanni. Highly purified cyanobacterin was found to inhibit the growth of many cyanobacteria at a minimum effective dose of 2 g/ml (4.6 M). The antibiotic had no effect on eubacteria including the photosynthetic Rhodospirillum rubrum. The site of action of cyanobacterin was further investigated in the unicellular cyanobacterium, Synechococcus sp. Electron micrographs of antibiotic-treated Synechococcus cells indicated that cyanobacterin affects thylakoid membrane structure. The antibiotic also inhibited light-dependent oxygen evolution in Synechococcus cells and in spheroplasts. These data support our conclusion that cyanobacterin specifically inhibits photosynthetic electron transport. This activity is similar to herbicides such as 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU). The anhydro analog of cyanobacterin had no biological activity.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl urea - DCPIP dichlorophenolindophenol     

Superoxide dismutases from a blue-green alga, Plectonema boryanum.

Iron-containing and manganese-containing superoxide dismutases were found in Plectonema boryanum. The Mn-enzyme occupies about 10% of total activity. The Fe-enzyme was purified to near homogeneity. It contains 2 atoms of iron per mol. Its molecular weight is 41,700 and it is composed of two subunits of identical molecular weight without disulfide linkage. Amino acid composition is presented. Electron paramagnetic resonance spectrum revealed that iron occurs in a high spin ferric form and in some anisotropic environment. The absorption spectrum and the absence of acid-labile enzymes are insensitive to cyanide. Although the Fe-enzyme is sensitive to hydrogen peroxide, the Mn-enzyme is not.     

Electron microscopy of polyphosphate bodies in a blue-green alga,Nostoc pruniforme

Summary Preparations of the blue-green alga, Nostoc pruniforme, treated according to the lead-sulfide staining technique of Ebelet al. (1958b) were examined by light and electron microscopy. They were found to contain spherical, electron-dense bodies, generally in close association with the nucleoplasm and polyhedral bodies, and sometimes enclosed by a membrane. In preparations extracted with cold TCA prior to the application of the staining procedure, such electron-dense structures could no longer be found; electron microscopy revealed instead spherical, electron-transparent areas with an electron-dense periphery in positions generally occupied by the electron-dense bodies in preparations not extracted with TCA.     

Characteristics of a stable, filamentous mutant of a coccoid blue-green alga

Filamentous mutants were induced in a coccoid blue-green alga, Agmenellum quadruplicatum strain BG1, after treatment with N-methyl-N'-nitro-N-nitrosoguanidine (NTG). The mutants fall into two general classes: filaments with cross walls and filaments without cross walls. All mutants of these general types derived from BG1 are stable and have growth rates the same as or very similar to the wild type under a variety of conditions. Detailed examination of one mutant, 53SB2, revealed no difference in deoxyribonucleic acid content nor in base ratios. Mutant 53SB2 did not revert to the normal cell size and shape when grown under different physical conditions nor upon the addition of potential reversing agents to the basal medium. It is our general experience that filamentous mutants such as those described here in BG1 are commonly induced in other coccoid blue-green algae after NTG treatment.     

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.     

Intracellular localization of glycolate dehydrogenase in a blue-green alga

Glycolate dehydrogenase activity was detected in cell-free extracts of Oscillatoria sp. prepared by osmotic lysis of spheroplasts in 0.05 m potassium phosphate buffer, pH 7.5, containing 0.3 m mannitol. Most of the enzyme activity was found in a particulate fraction and localized in the photosynthetic lamellae after centrifugation in a discontinuous sucrose density gradient. Enzyme activity was detected in this fraction both in the presence and absence of the artificial electron acceptor 2,6-dichlorophenolindophenol (DPIP) and a low rate of O(2) uptake was detected in this lamellar fraction. Activity was lost from the lamellar fraction by repeated washing or by treatment with 0.005% Triton X-100 and the solubilized enzyme activity was DPIP-dependent. The data indicate that both glycolate dehydrogenase and its natural electron acceptor are bound to the photosynthetic lamellae in vivo. In contrast, catalase activity was found in the soluble cytoplasmic fraction.     

Anaerobic and aerobic hydrogen gas formation by the blue-green alga Anabaena cylindrica.

An investigation was made of certain factors involved in the formation of hydrogen gas, both in an anaerobic environment (argon) and in air, by the blue-green alga Anabaena cylindrica. The alga had not been previously adapted under hydrogen gas and hence the hydrogen evolution occurred entirely within the nitrogen-fixing heterocyst cells; organisms grown in a fixed nitrogen source, and which were therefore devoid of heterocysts, did not produce hydrogen under these conditions. Use of the inhibitor dichlorophenyl-dimethyl urea showed that hydrogen formation was directly dependent on photosystem I and only indirectly dependent on photosystem II, consistent with heterocysts being the site of hydrogen formation. The uncouplers carbonyl cyanide chlorophenyl hydrazone and dinitrophenol almost completely inhibited hydrogen formation, indicating that the process occurs almost entirely via the adenosine 5'-triphosphate-dependent nitrogenase. Salicylaldoxime also inhibited hydrogen formation, again illustrating the necessity of photophosphorylation. Whereas hydrogen formation could usually only be observed in anaerobic, dinitrogen-free environments, incubation in the presence of the dinitrogen-fixing inhibitor carbon monoxide plus the hydrogenase inhibitor acetylene resulted in significant formation of hydrogen even in air. Hydrogen formation was studied in batch cultures as a function of age of the cultures and also as a function of culture concentration, in both cases the cultures being harvested in logarithmic growth. Hydrogen evolution (and acetylene-reducing activity) exhibited a distinct maximum with respect to the age of the cultures. Finally, the levels of the protective enzyme, superoxide dismutase, were measured in heterocyst and vegetative cell fractions of the organism; the level was twice as high in heterocyst cells (2.3 units/mg of protein) as in vegetative cells (1.1 units/mg of protein). A simple procedure for isolating heterocyst cells is described.     

Two plant-type ferredoxins from a blue-green alga, Nostoc verrucosum.

Two plant-type ferredoxins were isolated and purified from a blue-green alga, Nostoc verrucosum. They were separable by chromatography on a DEAE-cellulose column. The slow-moving band was designated ferredoxin I (Fd I) and the fast-moving band was ferredoxin II (Fd II). The ratio of the yield of ferredoxins I and II was about 1 : 0.84. Both ferredoxins had absorption spectra similar to those of plant-type ferredoxins. Two atoms of non-heme iron and two of labile sulfur were found per mol of both ferredoxin I and ferredoxin II. Their molecular weights were identical and estimated to be about 18 000 by a gel filtration method. The biochemical activities of these Nostoc ferredoxins were studied: the NADP photoreduction activity on one hand and the NADP-cytochrome c reductase activity on the other.     

Phosphorus uptake and growth of blue-green alga, Microcystis aeruginosa

The specific uptake rate Q(p) of orthophosphate (expressed throughout as phosphorus) and the specific growth rate mu of Microcystis aeruginosa were measured using batch-precultured cells, whose growth phase, and intracellular and extracellular phosphorus concentrations f(p) and P, respectively, had been changed. When the cells from phosphorus-rich precultures were used, smaller values of Q(p) (0.1-0.3 mug P mg dry wt. (-1) h (-1)) were observed. However, if phosphorusstarved cells were used, the initial value of Q(p) was enhanced to more than ten times those smaller values referred to above, but declined rapidly with time after the transfer. Q(p) leveled off at around t = 4 h, when f(p) approached the maximum value, even if phosphorus was still available in the medium. A new correlation was presented here with respect to Q(p) as a function of P and f(p) as follows: \documentclass{article}\pagestyle{empty}\begin{document}$$ Q_p = Q_{p,\max } \frac{P}{{K_p + P}}\frac{{(f_{p,\max } - f_p )}}{{(f_{p,\max } - f_p )}} $$\end{document} Although numerical values of parameters involved in the equation depend on physiological state (or preculture history) of the cells, the above equation could account not only for phosphorus uptake, during which changes in phosphorus content in the cells were observed, but also for initial rates of uptake presented previously by other workers. mu Values were confirmed to be a hyperbolic function of f(p) as has been suggested by previous workers.     

Inhibition of nitrate uptake by ammonia in a blue-green alga,Anabaena cylindrica

Ammonia at concentrations above 1×10^-5 M inhibits uptake of nitrate in the nitrogen-fixing blue-green alga, Anabaena cylindrica. This inhibition takes place both in the light and in the dark. The rate of nitrate uptake is stimulated by light. Addition of relatively high concentrations of nitrate (1–10 mM) reversibly inhibits ammonia uptake. FCCP, an uncoupler of phosphorylation, inhibits both nitrate and ammonia uptake. Ammonia may inhibit nitrate uptake by reducing the supply of energy (ATP) for active nitrate transport.Abbreviations FCCP carbonyl cyanide p-trifluoromethoxy-phenylhydrazone - CCCP carbonyl cyanide m-chlorophenyl-hydrazone