Presentation Information
[P02-192]Effects of nitrogen and sulfur sources on the photoautotrophic production of astaxanthin by Haematococcus pluvialis
Keishin Ide1, Kotaro Kataoka1, Kotaro Miyake1, Hideki Yamaji1, ○Tomohisa Katsuda1 (1. Kobe University (Japan))
Keywords:
Haematococcus pluvialis,Astaxanthin,Red vegetative cells
The green alga Haematococcus pluvialis is a primary source of astaxanthin (AX), a potent antioxidant used in health foods and cosmetics. AX production typically employs a two-stage process: a growth phase for vegetative cell proliferation and a production phase for AX accumulation in cyst cells. This study investigated how the concentration and timing of addition of nitrogen (nitrate) and sulfur (sulfate) sources influence cell growth and AX yield.
In the experiments, Molina's standard inorganic medium including 12 mM NaNO3 and 0.2 mM MgSO4 as principal nitrogen and sulfur sources was used for the photoautotrophic cultivation of H. pluvialis NIES-144. Bubble column photobioreactors with the working volume of 180 mL were used and fluorescent lamps were employed for light supply. The cultivation temperature (20/27°C) and light intensity (70/210 µmol·m-2·s-1) were cyclically changed in every 12 h during the growth phase. AX production was induced by elevating light intensity (to 500 µmol·m-2·s-1), temperature (to 30.5°C), and iron concentration (to 450 μM).
Regarding the nitrogen source, reducing the initial nitrate concentration in the medium from 12 mM to 8.4–9.6 mM significantly enhanced AX productivity. Lower nitrate levels resulted in lower cell densities, which increased the relative light intensity per cell. Consequently, the morphological transition from vegetative to cyst cells was accelerated and the AX productivity improved by 40–50% compared to the control. Regarding the sulfur source, we observed that sulfate depletion in the growth phase induced red-colored motile vegetative cells by day 2. These cells that accumulated AX while retaining flagella are rarely reported with clarified conditions. Although low initial sulfate triggered early AX biosynthesis, it also limited cell proliferation, leading to a decrease in total AX yield. To overcome this growth limitations, sulfate addition during the AX production phase was examined: Maintaining a low sulfate concentration (0.05 mM) during this phase increased AX production by approximately 30% compared to the control where sulfate was allowed to deplete. This method successfully balanced the induction of AX production with the nutrient requirements for cell growth and maintenance.
In conclusion, reducing nitrate in the growth phase and maintaining a low sulfate concentration during the AX production phase are effective strategies for optimizing AX production.
In the experiments, Molina's standard inorganic medium including 12 mM NaNO3 and 0.2 mM MgSO4 as principal nitrogen and sulfur sources was used for the photoautotrophic cultivation of H. pluvialis NIES-144. Bubble column photobioreactors with the working volume of 180 mL were used and fluorescent lamps were employed for light supply. The cultivation temperature (20/27°C) and light intensity (70/210 µmol·m-2·s-1) were cyclically changed in every 12 h during the growth phase. AX production was induced by elevating light intensity (to 500 µmol·m-2·s-1), temperature (to 30.5°C), and iron concentration (to 450 μM).
Regarding the nitrogen source, reducing the initial nitrate concentration in the medium from 12 mM to 8.4–9.6 mM significantly enhanced AX productivity. Lower nitrate levels resulted in lower cell densities, which increased the relative light intensity per cell. Consequently, the morphological transition from vegetative to cyst cells was accelerated and the AX productivity improved by 40–50% compared to the control. Regarding the sulfur source, we observed that sulfate depletion in the growth phase induced red-colored motile vegetative cells by day 2. These cells that accumulated AX while retaining flagella are rarely reported with clarified conditions. Although low initial sulfate triggered early AX biosynthesis, it also limited cell proliferation, leading to a decrease in total AX yield. To overcome this growth limitations, sulfate addition during the AX production phase was examined: Maintaining a low sulfate concentration (0.05 mM) during this phase increased AX production by approximately 30% compared to the control where sulfate was allowed to deplete. This method successfully balanced the induction of AX production with the nutrient requirements for cell growth and maintenance.
In conclusion, reducing nitrate in the growth phase and maintaining a low sulfate concentration during the AX production phase are effective strategies for optimizing AX production.
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