Combined artificial high-silicate medium and LED illumination promote carotenoid accumulation in the marine diatom Phaeodactylum tricornutum

Abstract

BackgroundDiatoms, which can accumulate large amounts of carotenoids, are a major group of microalgae and the dominant primary producer in marine environments. Phaeodactylum tricornutum, a model diatom species, acquires little silicon for its growth although silicon is known to contribute to gene regulation and play an important role in diatom intracellular metabolism. In this study, we explored the effects of artificial high-silicate medium (i.e. 3.0 mM sodium metasilicate) and LED illumination conditions on the growth rate and pigment accumulation in P. tricornutum, which is the only known species so far that can grow without silicate. It’s well known that light-emitting diodes (LEDs) as novel illuminants are emerging to be superior monochromatic light sources for algal cultivation with defined and efficient red and blue lights.ResultsFirstly, we cultivated P. tricornutum in a synthetic medium supplemented with either 0.3 mM or 3.0 mM silicate. The morphology and size of diatom cells were examined: the proportion of the oval and triradiate cells decreased while the fusiform cells increased with more silicate addition in high-silicate medium; the average length of fusiform cells also slightly changed from 14.33 µm in 0.3 mM silicate medium to 12.20 µm in 3.0 mM silicate medium. Then we cultivated P. tricornutum under various intensities of red light in combination with the two different levels of silicate in the medium. Higher biomass productivity also achieved in 3.0 mM silicate medium than in 0.3 mM silicate medium under red LED light irradiation at 128 μmol/m2/s or higher light intensity. Increasing silicate reversed the down-regulation of fucoxanthin and chlorophyll a under high red-light illumination (i.e. 255 μmol/m2/s). When doubling the light intensity, fucoxanthin content decreased under red light but increased under combined red and blue (50:50) lights while chlorophyll a content reduced under both conditions. Fucoxanthin accumulation and biomass productivity increased with enhanced red and blue (50:50) lights.ConclusionHigh-silicate medium and blue light increased biomass and fucoxanthin production in P. tricornutum under high light conditions and this strategy may be beneficial for large-scale production of fucoxanthin in diatoms.

Red Light Variation an Effective Alternative to Regulate Biomass and Lipid Profiles in Phaeodactylum tricornutum

“…In addition, our results confirm observations from another study on the impact of red light where biomass increased by 40% under enriched red light [40]. Similarly, another study reported better growth and higher fucoxanthin content in P. tricornutum under red and blue light [30]. That study is similar to our treatment RS, where we have supplied a red wavelength for the first 7 days and then exposed the culture to the white light during the stationary phase.…”

“…Indeed, at day 11, the RS growth was significantly higher with 22% and 14% more cells than continuous W and R light, respectively ( Figure 2). The cell growth observed under R and RS treatment can be explained, in part, by the presence of a wide range of photoreceptors with the ability to sense red/far-red wavelengths and their potential to prevent photoinhibition [30,32]. A similar study has reported the increasing growth of P. tricornutum under defined and efficient combinations of red and blue lights [30].…”

“…The cell growth observed under R and RS treatment can be explained, in part, by the presence of a wide range of photoreceptors with the ability to sense red/far-red wavelengths and their potential to prevent photoinhibition [30,32]. A similar study has reported the increasing growth of P. tricornutum under defined and efficient combinations of red and blue lights [30]. Another study has shown the positive impact of supplementing different light colors on Chlamydomonas reinhardtii culture [13].…”

“…Furthermore, many studies have shown a positive trend of red light with an increase in the specific growth rate and lipid production in Chlorella, Botryococcus, and Nannochloropsis [7,26,29]. Another study showed a positive trend of the combined impact of red and blue light on biomass productivity and fucoxanthin production in P. tricornutum [30]. However, contrasting results have been reported where they observed high productivity under yellow light as compared to red and blue light for Chlamydomonas reinhardtii [13].…”

“…It is interesting to note the 1.8 fold increase in lipid from R to RS, which suggests that shifting from red light to full spectrum during the stationary phase has an impact on lipid accumulation. It is known that the usual change in the lipid composition is influenced by the cellular C/N ratio, light intensity, nutrient depletion, and other possible inducible biotic/abiotic stress conditions [28][29][30]. An increase in C/N ratio, lipid, and carbohydrate in red light acclimated P. tricornutum culture has been reported [11].…”