Assessment of the impact of salinity and irradiance on the combined carbon dioxide sequestration and carotenoids production by Dunaliella salina: A mathematical model.

Current anthropogenic activities have been causing a significant increase in the atmospheric concentration of CO2 over the past 60 years. To mitigate the consequent global warming problem, efficient technological solutions, based on economical and technical grounds, are required. In this work, microalgae are studied as important biological systems of CO2 fixation into organic compounds through photosynthesis. These microorganisms are potential sources of a wide variety of interesting chemical compounds, which can be used for commercial purposes, reducing the cost of CO2 capture and sequestration. Specifically, Dunaliella salina culture was studied aiming at the impact evaluation of operational conditions over cellular growth and carotenoid production associated with the CO2 sequestration on focus. The main experimental parameters investigated were salinity and irradiance conditions. The experimental results supported the development of a descriptive mathematical model of the process. Based on the proposed model, a sensitivity analysis was carried out to investigate the operational conditions that maximize CO2 consumption and carotenoid production, in order to guide further development of technological routes for CO2 capture through microalgae. A preliminary cost estimation of CO2 sequestration combined to carotenoids production for a 200 MW power plant is presented, based on the growth rates achieved in this study.

Effect of the respiratory activity on photoinhibition of the cyanobacterium Synechocystis sp.

The influence of respiratory activity on photosynthesis in Synechocystis cells that had been exposed to high light intensity was studied using distinct conditions of nitrogen supply. The photoinhibitory rate of N-sufficient cells was not influenced by the presence of different nitrogen sources. In contrast, when N-starved cells were resupplied with ammonium, they were protected from photoinhibition. Although N-starved cells presented a higher rate of dark O(2) uptake than N-sufficient ones, the photoinhibitory rate increased in both cases after addition of sodium azide or sodium azide plus salicylhydroxamic acid in the photoinhibitory treatment. In the absence of the D(1) protein repair mechanism, photodamage to Photosystem II was faster in N-sufficient cells than in N-starved ones. Mitigation of photodamage disappeared when the respiratory activity of N-starved cells was partially suppressed by the addition of sodium azide or sodium azide and salicylhydroxamic acid. Our results suggest that electron flow through cyanobacterial terminal oxidases can assist Photosystem I in removing electrons from the reduced plastoquinone pool, thus contributing to both reopening of Photosystem II reaction centers and avoiding photogeneration of reactive oxygen species under photoinhibitory conditions.

Effects of the Alkaloid Gramine on the Light-Harvesting, Energy Transfer, and Growth of Anabaena sp. (PCC 7119).

Long-term and short-term effects of gramine on cells of Anabaena sp. were studied. Culture death was observed after an initial growth in the presence of 0.5 mM gramine, and lower concentrations decreased both the specific growth rate and the growth yield. Cultures showed a reduction in the chlorophyll content as well as an increase in the level of accessory pigments, which were proportional to the alkaloid concentration. When cultures were excited with green light in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the fluorescence spectra of the cells showed a shoulder at 685 nm related to the photosystem II (PSII) antennae emission. This band was reduced when gramine was present during the growth, suggesting that gramine suppresses the energy transfer between the phycobilisomes and PSII. At lethal concentrations for cellular growth, gramine suppressed immediately the photosynthetic oxygen production as well as the electron transport from H2O to p-benzoquinone. The influence of gramine on the PSII photochemical reactions was investigated by flash-induced fluorescence measurements, and the results suggest that the alkaloid could act as an electron donor to the PSII reaction center.

Pressure and low temperature effects on the fluorescence emission spectra and lifetimes of the photosynthetic components of cyanobacteria.

The effects of hydrostatic pressure on the excited state reactions of the photosynthetic system of cyanobacteria were studied with the use of stationary and dynamic fluorescence spectroscopy. When the cells were excited with blue light (442 nm), hydrostatic pressure promoted a large increase in the fluorescence emission of the phycobilisomes (PBS). When PBS were excited at 565 nm, the shoulder originating from photosystem II (PSII) emission (F685) disappeared under 2.4 kbar compression, suggesting suppression of the energy transfer from PBS to PSII. At atmospheric pressure, the excited state decay was complex due to energy transfer processes, and the best fit to the data consisted of a broad Lorentzian distribution of short lifetimes. At 2.4 kbar, the decay data changed to a narrower distribution of longer lifetimes, confirming the pressure-induced suppression of the energy transfer between the PBS and PSII. When the cells were excited with blue light, the decay at atmospheric pressure was even more complex and the best fit to the data consisted of a two-component Lorentzian distribution of short lifetimes. Under compression, the broad distribution of lifetimes spanning the region 100-1,000 ps disappeared and gave rise to the appearance of a narrow distribution characteristic of the PBS centered at 1.2 ns. The emission of photosystem I underwent 2.2-fold increase at 2.4 kbar and room temperature. A decrease in temperature from 20 to -10 degrees C at 2.4 kbar promoted a further increase in the fluorescence emission from photosystem I to a level comparable with that obtained at temperatures below 120 degrees K and atmospheric pressure. On the other hand, when the temperature was decreased under pressure, the PBS emission diminished to very low value at blue or green excitation, suggesting the disassembly into the phycobiliprotein subunits.

Effect of K+ on phosphorylation of the sarcoplasmic reticulum ATPase by either Pi or ATP.

The effect of K+ on phosphorylation of the Ca2+-dependent ATPase of the sarcoplasmic reticulum by either Pi or ATP was studied using a millisecond mixing and quenching device. Equilibrium levels of phosphoenzyme formed by Pi were progressively decreased in the presence of increasing K+ concentrations. This effect was more pronounced in empty vesicles than in vesicles previously loaded with calcium. Potassium did not modify the initial rate of enzyme phosphorylation by Pi but increased the rate of phosphoenzyme hydrolysis 4- to 6-fold. Using low ATP concentration (50 micro M), the steady state level of phosphoenzyme was decreased by the addition of K+. This effect disappeared when the ATP concentration was raised to 1 mM.