Abstract
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.
Highlights
Diatoms are important primary producers in fresh and seawater environments
The growth of seawater and freshwater diatom species grown at atmospheric CO2 (400 ppm; low) or at high CO2 (20,000 ppm) was followed by measuring the optical density of the cultures at 750 nm (Figure 1).From all diatom species studied, the growth of A. formosa was the most affected in cells grown at high CO2 and the calculated growth rate was 0.57 ± 0.09 day−1 at high CO2 and
We observed that the growth of T. pseudonana cells cultured at high CO2 was arrested after six days with a concomitant strong cell flocculation and precipitation, impeding the continuity of these cultures
Summary
Diatoms are important primary producers in fresh and seawater environments. They contribute up to 20% of global CO2 fixation [1]. Chrysolaminarin is stored in the vacuole [3], while lipids are accumulated in diatoms mainly as oil bodies in the cytoplasm and, in less amounts, in the chloroplasts [4]. Lipid accumulation in some microalgae species can reach up to 73% of their dry weight and show higher productivities compared to crop plants [9,10]. Diatoms have emerged as a good source of lipids because of their exceptional photosynthetic efficiency and their ability to accumulate high amounts of lipids in many different culture conditions [6,11,12,13]
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