Peter Fay

Cell differentiation and pigment composition in Anabaena cylindrica

SummaryCell differentiation in Anabaena cylindrica is accompanied with characteristic changes in the pigment composition of heterocysts and spores. In both the absence of phycocyanin is consistent with the lack of CO2-fixing ability previously reported. The presence of chlorophyll and β-carotene suggests a functional photosystem I in heterocysts. In the spores chlorophyll is largely replaced by pheophytin. The quantitative distribution of carotenoids is also affected. An increase in the proportion of β-carotene is characteristic of heterocysts while spores show a larger proportion of xanthophylls compared with the intact filament.

Special aspects of nitrogen fixation by blue-green algae

When carbon dioxide fixation was over 90 % inhibited by CMU, nitrogen fixation remained unaffected in nitrogen-starved cells of Anabaena cylindrica. In normal cells under the same conditions nitrogen fixation was about 50 % inhibited by CMU. These data suggest, first, that nitrogen fixation in this organism is independent of reducing potential generated by non-cyclic photo-electron transport and, secondly, that nitrogen fixation is stimulated by photosynthetically produced carbon skeletons to assimilate the fixed nitrogen. Although nitrogen fixation occurred to a limited extent in the dark, increasing light intensity stimulated nitrogen fixation both in the presence and absence of CMU. This suggests that light-generated ATP is required for nitrogen fixation in this alga. A ratio of pyruvate decarboxylation to nitrogen fixation of 3:1 has been established for A. cylindrica. This accords with the hypothesis that pyruvate acts as a hydrogen donor for nitrogen reduction and that provision of the required reductant is independent of photosynthesis in blue-green algae.

Nitrogen metabolism and ultrastructure inAnabaena cylindrica

The structural and functional symptoms of molybdenum deficiency inAnabaena cylindrica grown in a medium without combined nitrogen and thus dependent on fixation of elemental nitrogen, resemble those brought about by nitrogen starvation. However, the substantially increased rate of heterocyst differentiation in this culture is not accompanied by a corresponding increase in nitrogenase activity; on the contrary, enzyme activity is severely impaired in the absence of molybdenum. When the supply of molybdenum, or of ammonia, is restored, the alga recovers rapidly. Vanadium exerts an inhibitory effect upon nitrogen-fixing ability of the alga, and its presence in the molybdenum-deficient culture results in the amplification of the symptoms of mlybdenum deficiency.

Photostimulation of nitrogen fixation in Anabaena cylindrica

Abstract Photostimulation of N 2 fixation in the blue-green alga Anabaena cylindrica was investigated using monochromatic light and by comparing action spectra of C 2 H 2 reduction with that of photosynthetic O 2 evolution. Maximum nitrogenase activity per unit energy was measured at a wavelength which corresponds to the maximum light absorption of chlorophyll a . The action spectrum of C 2 H 2 reduction indicates a primary involvement of Photosystem I in N 2 fixation by blue-green algae.

Tetrazolium reduction and nitrogenase activity in heterocystous blue-green algae.

SummaryHeterocysts reduce triphenyl tetrazolium chloride (TTC) faster than vegetative cells apparently because the absence of the O2-evolving photosystem II and the high electron transport activity in these cells. Although the rate of TTC reduction in vegetative cells is increased by the continuous removal of O2 evolved in photosynthesis, it has not been possible to obtain rates of TTC reduction comparable with those in heterocysts probably because of the continued competition for electrons between TTC and O2. The use of nitro-blue tetrazolium chloride (NBT) as a redox indicator has revealed the presence in filaments under aerobic conditions of a gradient of electron transport activity with strongest reducing power in the heterocysts, proheterocysts and vegetative cells next to heterocysts, and with gradually diminishing activity midway between two heterocysts. This pattern is indistinct in filaments grown under micro-aerophilic conditions. The strong electron transport activity in vegetative cells adjacent to heterocysts appears to promote reducing conditions in the heterocysts. Both, red-formazan formation in the heterocysts and blue-formazan deposition in vegetative cells greatly inhibit nitrogenase activity, and this was adversely affected also by the detachment of heterocysts from vegetative cells. The findings are consistent with the idea that the association of heterocysts with vegetative cells in essential for nitrogen fixation to occur in heterocystous blue-green algae.

Akinete development in the planktonic blue-green alga Anabaena circinalis

Akinete development in Anabaena circinalis, which characteristically begins in vegetative cells two cells away from a heterocyst during the late exponential phase of growth in batch culture, coincides with the decline of nitrogenase activity and of heterocyst frequency. The trend of akinete production is inversely related to that of heterocyst differentiation. Akinete formation is suppressed by agitation and enhanced under undisturbed culture conditions. The latter permit surface accumulation of the buoyant filament material which leads to increased culture density, decreased light penetration into culture medium and hence to limitation of light-dependent reactions. The conditions resemble those present in surface blooms of buoyant planktonic populations in the natural habitat and in temperate eutrophic lakes in general. No conclusive evidence was obtained that the depletion of mineral nutrients is responsible for the initiation of akinete differentiation. Treatments like orthophosphate supplementation, t...

Blue-green algal growth and sporulation in response to simulated surface bloom conditions

Physical and chemical factors were investigated for their effect on growth and differentiation of unialgal isolates and natural planktonic populations of blue-green algae from the Salopian meres under laboratory conditions. Most extensively investigated were two strains of Aphanizomenon flos-aquae (L.) Ralfs. Deficiencies of orthophosphate and nitrate, and of minor elements, were found to reduce growth but not to stimulate sporulation. N-glycyl-glycine inhibited both heterocyst differentiation and sporulation, and HEPES stimulated sporulation; but extracellular compounds contained in filtrates from sporulating cultures had no effect on morphology. Exposures to extremes of light intensity, and to u.v. light of 365 nm reduced and often stopped growth, but did not induce akinete formation in either of the algal isolates or in any of the populations collected from the lakes.

A simple apparatus for the continuous culture of photosynthetic micro-organisms

A simple inexpensive all-glass culture apparatus for the continuous culture of micro-algae and photosynthetic bacteria is described. The basic apparatus can be equipped with a metering pump and an overflow device for automatic uninterrupted operation, or it can be operated manually with periodic sampling and adjustment of population density.

Oxygen inhibition of nitrogen fixation in cell-free preparations of blue-green algae

Abstract 1. Factors inhibiting N 2 fixation in cell-free preparations of two blue-green algae, Anabaena cylindrica and Chlorogloea fritschii were investigated. 2. 15 N uptake by particulate cell-free fractions of A. cylindrica was less in the light than in the dark, indicating some photo-inhibition of N 2 fixation. 3. Anaerobic conditions during preparation and incubation of particulate cell-free fractions of C. fritschii greatly increased their N 2 -fixing ability. 4. Soluble cell-free material was found to have an inhibitory effect on N 2 fixation by particulate cell-free preparations obtained from A. cylindrica . This inhibition was approximately proportional to the amount of soluble fraction supplied to the particulate material. Dialysis of the soluble cell-free fraction did not remove the inhibition which has therefore been attributed to the presence of a soluble enzyme, possibly an oxidase. 5. Dialysis of the soluble cell-free fraction or of particulate material suspended with soluble cell-free fraction resulted in a slight decrease of 15 N uptake, indicating the removal by dialysis of small-molecule factors required for N 2 fixation. 6. The presence of sulphydryl agents increased the rate of N 2 fixation in cell-free preparations of A. cylindrica .

Interaction between light quality and nitrogen availability in the differentiation of akinetes in the planktonic cyanobacterium Gloeotrichia echinulata

Akinete differentiation in Gloeotrichia echinulata is stimulated in batch cultures in the absence of a source of combined nitrogen. When inorganic nitrogen is available in the medium, the logarithmic phase of growth is prolonged and akinetes form at a higher culture density than when dinitrogen is supplied as the sole source of this element. Light quality also influences the timing of akinete differentiation; akinetes are formed at a lower culture density in green light in comparison to white light, particularly in the absence of combined nitrogen. These observations are interpreted in terms of the light-energy requirement for the maintenance of growth and the spectral requirements for nitrogen fixation in cultures free of combined nitrogen. The data are related to the influence of variations in underwater light climate on the development of akinetes in natural populations of planktonic blue-green algae.