Accumulation of reserve compounds (i.e., lipids and chrysolaminarin) in diatoms depends on the environmental conditions, and is often triggered by stress conditions, such as nutrient limitation. Manipulation of CO2 supply can also be used to improve both lipids and carbohydrates accumulation. Given the high diversity among diatoms, we studied the two marine model diatoms—Thalassiosira pseudonana and Phaeodactylum tricornutum, a freshwater diatom, Asterionella formosa, and Navicula pelliculosa—found in fresh- and sea-water environments. We measured the accumulation of reserve compounds and the activity of enzymes involved in carbon metabolism in these diatoms grown at high and atmospheric CO2. We observed that biomass and lipid accumulation in cells grown at high CO2 differ among the diatoms. Lipid accumulation increased only in P. tricornutum and N. pelliculosa grown in seawater in response to elevated CO2. Moreover, accumulation of lipids was also accompanied by an increased activity of the enzymes tested. However, lipid accumulation and enzyme activity decreased in N. pelliculosa cultured in fresh water. Chrysolaminarin accumulation was also affected by CO2 concentration; however, there was no clear relation with lipids accumulation. Our results are relevant to understand better the ecological role of the environment in the diatom adaptation to CO2 and the mechanisms underpinning the production of storage compounds considering diatom diversity.

ARTICLEResponse to oxidative stress induced by high light and carbon dioxide (CO 2 ) in the biodiesel producer model Nannochloropsis salina (Ochrophyta, Eustigmatales)Respuesta a estrés oxidativo generado por alta luz y dióxido de carbono (CO 2 ) en el modelo productor de biodiesel Nannochloropsis salina (Ochrophyta, Eustigmatales) Resumen.-Producto del agotamiento de los recursos mundiales de combustibles fósiles, las microalgas han tomado fuerza como alternativa de biocombustible. Buscando hacer sustentable el proceso, en general se propone realizar los cultivos acoplados a fuentes de emisión de CO 2 , logrando con ello mayores rendimientos en biomasa y mitigando la huella de carbono de los procesos de combustión. Nannochloropsis salina es una microalga de la familia Monodopsidaceae de fácil crecimiento y que produce compuestos de valor comercial, tales como pigmentos esenciales, ácidos grasos poliinsaturados y alta cantidad de lípidos. Estudios previos muestran que en presencia de algunas concentraciones de CO 2 (hasta 2%) se produce un aumento de la biomasa y de la producción de ácidos grasos. Sin embargo, estas condiciones traen consigo una acidificación del medio, condición que afecta la eficiencia del proceso de fotosíntesis y promueve la generación de especies reactivas de oxígeno. En este trabajo, se estudió la respuesta antioxidante de cultivos de Nannochloropsis salina suplementados con CO 2 , por medio de 3 metodologías: analizando la actividad enzimática antioxidante (catalasa, ascorbato peroxidasa y peroxirredoxina), cuantificando los compuestos fenólicos, H 2 O 2 y lipoperóxidos (i.e., marcador de daño celular) y evaluando los niveles de expresión génica. Los resultados sugieren que un aumento en la concentración de CO 2 en el cultivo, junto con alta luz, induce una condición de estrés oxidativo en Nannochloropsis salina. Sin embargo, la respuesta celular observada en esta microalga logra atenuar este estrés, sin afectar su rendimiento global. KarenPalabras clave: Nannochloropsis salina, especies reactivas de oxígeno, enzimas antioxidantes, dióxido de carbono, qPCRAbstract.-Due to overconsumption of fossil fuels, microalgae have arrived as an alternative source of biofuel. Looking forward to generate a sustainable process, it is proposed to couple the cultures to CO 2 emission sources, reaching in this way higher biomass performance and helping in the way with the capture of carbon released by the combustion processes. Nannochloropsis salina is a microalgae from the Monodopsidaceae family, which is easy to grow and produces high value compounds like essential pigments, polyunsaturated fatty acids and high amounts of lipids. Previous studies showed that adding CO 2 to cultures (until 2%) generated an increment in biomass and in the production of fatty acids. However, these conditions also induce acidification of the media, a condition that may promote the generation of oxygen reactive species. In this work, the antioxidant performance of N. salina was studied under different culture conditions invo...