Low oxygen levels contribute to improve photohydrogen production in mixotrophic non‑stressed Chlamydomonas cultures

Background: Currently, hydrogen fuel is derived mainly from fossil fuels, but there is an increasing interest in clean and sustainable technologies for hydrogen production. In this context, the ability of some photosynthetic microorganisms, particularly cyanobacteria and microalgae, to produce hydrogen is a promising alternative for renewable, clean-energy production. Among a diverse array of photosynthetic microorganisms able to produce hydrogen, the green algae Chlamydomonas reinhardtii is the model organism widely used to study hydrogen production. Despite the well-known fact that acetate-containing medium enhances hydrogen production in this algae, little is known about the precise role of acetate during this process. Results: We have examined several physiological aspects related to acetate assimilation in the context of hydrogen production metabolism. Measurements of oxygen and CO2 levels, acetate uptake, and cell growth were performed under different light conditions, and oxygenic regimes. We show that oxygen and light intensity levels control acetate assimilation and modulate hydrogen production. We also demonstrate that the determination of the contribution of the PSII-dependent hydrogen production pathway in mixotrophic cultures, using the photosynthetic inhibitor DCMU, can lead to dissimilar results when used under various oxygenic regimes. The level of inhibition of DCMU in hydrogen production under low light seems to be linked to the acetate uptake rates. Moreover, we highlight the importance of releasing the hydrogen partial pressure to avoid an inherent inhibitory factor on the hydrogen production. Conclusion: Low levels of oxygen allow for low acetate uptake rates, and paradoxically, lead to efficient and sustained production of hydrogen. Our data suggest that acetate plays an important role in the hydrogen production process, during non-stressed conditions, other than establishing anaerobiosis, and independent of starch accumulation. Potential metabolic pathways involved in hydrogen production in mixotrophic cultures are discussed. Mixotrophic nutrient-replete cultures under low light are shown to be an alternative for the simultaneous production of hydrogen and biomass

Dietary α‐Linolenic Acid, Marine ω‐3 Fatty Acids, and Mortality in a Population With High Fish Consumption: Findings From the PREvención con DIeta MEDiterránea (PREDIMED) Study

Background: Epidemiological evidence suggests a cardioprotective role of α‐linolenic acid (ALA), a plant‐derived ω‐3 fatty acid. It is unclear whether ALA is beneficial in a background of high marine ω‐3 fatty acids (long‐chain n‐3 polyunsaturated fatty acids) intake. In persons at high cardiovascular risk from Spain, a country in which fish consumption is customarily high, we investigated whether meeting the International Society for the Study of Fatty Acids and Lipids recommendation for dietary ALA (0.7% of total energy) at baseline was related to all‐cause and cardiovascular disease mortality. We also examined the effect of meeting the society's recommendation for long‐chain n‐3 polyunsaturated fatty acids (≥500 mg/day). Methods and Results: We longitudinally evaluated 7202 participants in the PREvención con DIeta MEDiterránea (PREDIMED) trial. Multivariable‐adjusted Cox regression models were fitted to estimate hazard ratios. ALA intake correlated to walnut consumption (r=0.94). During a 5.9‐y follow‐up, 431 deaths occurred (104 cardiovascular disease, 55 coronary heart disease, 32 sudden cardiac death, 25 stroke). The hazard ratios for meeting ALA recommendation (n=1615, 22.4%) were 0.72 (95% CI 0.56–0.92) for all‐cause mortality and 0.95 (95% CI 0.58–1.57) for fatal cardiovascular disease. The hazard ratios for meeting the recommendation for long‐chain n‐3 polyunsaturated fatty acids (n=5452, 75.7%) were 0.84 (95% CI 0.67–1.05) for all‐cause mortality, 0.61 (95% CI 0.39–0.96) for fatal cardiovascular disease, 0.54 (95% CI 0.29–0.99) for fatal coronary heart disease, and 0.49 (95% CI 0.22–1.01) for sudden cardiac death. The highest reduction in all‐cause mortality occurred in participants meeting both recommendations (hazard ratio 0.63 [95% CI 0.45–0.87]). Conclusions: In participants without prior cardiovascular disease and high fish consumption, dietary ALA, supplied mainly by walnuts and olive oil, relates inversely to all‐cause mortality, whereas protection from cardiac mortality is limited to fish‐derived long‐chain n‐3 polyunsaturated fatty acids. Clinical Trial Registration URL: http://www.Controlled-trials.com/. Unique identifier: ISRCTN35739639

Optimización de la producción de hidrógeno en el alga Chlamydomonas mediante el uso de mutantes y condiciones de cultivo no estresantes

Para promover la producción de H2 por Chlamydomonas se utilizan normalmente condiciones de deficiencia nutricional. En esta Tesis se describe la producción sostenida de H2 por Chlamydomonas en medio de cultivo rico gracias al descenso de la intensidad lumínica, la liberación de la presión parcial de H2 en el espacio de cabeza de los cultivos y el suplemento discontinuo de O2. Esta condición permite, además, el crecimiento del cultivo para la obtención simultánea de biomasa. Asimismo, se ha demostrado una relación directa entre el consumo de acetato y la producción de H2. Por otro lado, bajo la premisa de que un aumento en la producción de H2 puede lograrse mediante la disminución de la producción fotosintética de O2 o el aumento de las reservas de almidón, durante el desarrollo de esta Tesis Doctoral se ha escrutado parcialmente una colección de mutantes insercionales para la selección de aquellos con cada uno de estos fenotipos.In order to promote the H2 production by Chlamydomonas, some nutrients are frequently removed from the culture medium. This Thesis describes how to get a sustained H2-production using Chlamydomonas cultures growing in replete-media (without nutritional deficiency) by decreasing light intensity, releasing H2 partial pressure in the culture’s headspace and supplying O2. This culture conditions let the culture grow, getting H2 and biomass simultaneously. Likewise, a direct relationship between H2 production and acetate uptake has been reported. On the other hand, it is believed that a lower photosynthetic O2 production or higher starch reserves in the cell can produce an increase in H2 production by Chlamydomonas. In this sense, an insercional-mutants library was partially screened to select those mutants with the desired phenotypes