Presentation Information
[P04-551]Effect of light/dark cycle on extracellular organic carbon production in the marine diatom Fistulifera solaris
○Taro Kaigawa1, Tsuyoshi Tanaka1, Kosuke Kataoka1,2 (1. Graduate School of Engineering, Tokyo University of Agriculture and Technology (Japan), 2. Comprehensive Research Organization, Waseda University (Japan))
Keywords:
Extracellular organic carbon,Microalgae,Diatom
[Purpose] Microalgae have attracted attention as promising hosts for sustainable production as they convert CO2 into diverse valuable metabolites through photosynthetic carbon fixation. However, downstream processing remains a major bottleneck, as most products require biomass harvesting and intracellular extraction. Recent reports have shown that several microalgal species can release water-soluble sugars into the surrounding culture medium, which could enable simpler and more cost-effective recovery than conventional extraction workflows. Nonetheless, the phenotype varies among species, and both the underlying mechanisms and cultivation condition to enhance sugar secretion remain poorly understood. Because photoperiod strongly effect carbon partitioning in microalgae, we hypothesized that light dark cycle conditions can modulate extracellular sugar accumulation. To test this, we evaluated the effect of photoperiod on extracellular sugar accumulation in industrially relevant microalgal strains.
[Method] The diatoms Phaeodactylum tricornutum and Fistuirifela solaris, and the green algae Tetraselmis sp. NKG400013 were cultured for 7 days. Extracellular organic carbon (EOC) was measured based on the non-purgeable organic carbon concentration using a total organic carbon analyzer. Next, for the species with the highest EOC, cultures were conducted for 7 days, 350 µmol photons/m2/s light intensity, and five L:D cycle conditions in an appropriate medium. The supernatant was collected and EOC was measured on day 7. Non-photochemical quenching (NPQ) was determined using the PAM fluorescence method.[Results&Consideration] Among the microalgal strains tested, F. solaris showed the highest EOC release, reaching 52.1 mg/l. To evaluate the effect of photoperiod on EOC release, we compared EOC accumulation during cultivation under 24 h:0 h, 18 h:6 h, 12 h:12 h and 6 h:18 h light dark cycles in F. solaris. The 18 h:6 h condition yielded the highest EOC, 62.3 mg/l. To assess how photoperiod influenced photosynthetic performance, we compared NPQ across the same conditions. NPQ decreased under 18 h:6 h relative to 24 h:0 h, from 62.3 mg/l to 28.3 mg/l. This suggests that introducing an appropriate dark period alleviates high light stress and improves photosynthetic performance. Under sustained high light stress, carbon fixation is reduced, which likely limits EOC accumulation in the medium. Assuming that all EOC measured in this study consisted of soluble sugars, the estimated sugar titer of F. solaris under the 18 h:6 h condition reached 1.56×102 mg/l. Overall, these results indicate that an appropriate light dark cycle can enhance extracellular sugar release by suppressing light stress.
[Conclusion] This study demonstrates that adjusting the photoperiod to 18 h:6 h contributes to efficient production of EOC in F. solaris.
[Method] The diatoms Phaeodactylum tricornutum and Fistuirifela solaris, and the green algae Tetraselmis sp. NKG400013 were cultured for 7 days. Extracellular organic carbon (EOC) was measured based on the non-purgeable organic carbon concentration using a total organic carbon analyzer. Next, for the species with the highest EOC, cultures were conducted for 7 days, 350 µmol photons/m2/s light intensity, and five L:D cycle conditions in an appropriate medium. The supernatant was collected and EOC was measured on day 7. Non-photochemical quenching (NPQ) was determined using the PAM fluorescence method.[Results&Consideration] Among the microalgal strains tested, F. solaris showed the highest EOC release, reaching 52.1 mg/l. To evaluate the effect of photoperiod on EOC release, we compared EOC accumulation during cultivation under 24 h:0 h, 18 h:6 h, 12 h:12 h and 6 h:18 h light dark cycles in F. solaris. The 18 h:6 h condition yielded the highest EOC, 62.3 mg/l. To assess how photoperiod influenced photosynthetic performance, we compared NPQ across the same conditions. NPQ decreased under 18 h:6 h relative to 24 h:0 h, from 62.3 mg/l to 28.3 mg/l. This suggests that introducing an appropriate dark period alleviates high light stress and improves photosynthetic performance. Under sustained high light stress, carbon fixation is reduced, which likely limits EOC accumulation in the medium. Assuming that all EOC measured in this study consisted of soluble sugars, the estimated sugar titer of F. solaris under the 18 h:6 h condition reached 1.56×102 mg/l. Overall, these results indicate that an appropriate light dark cycle can enhance extracellular sugar release by suppressing light stress.
[Conclusion] This study demonstrates that adjusting the photoperiod to 18 h:6 h contributes to efficient production of EOC in F. solaris.
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