Advantageous characteristics of the diatomChaetoceros gracilisas a sustainable biofuel producer.
BACKGROUND
Diatoms have attracted interest as biofuel producers. Here, the contents of lipids and photosynthetic pigments were analyzed in a marine centric diatom,Chaetoceros gracilis. This diatom can be genetically engineered using our previously reported transformation technique and has a potential to produce valuable materials photosynthetically. Sustainable culture conditions for cost-effective production of biological materials under autotrophic conditions with atmospheric carbon dioxide were investigated in the laboratory. A large-scale, open-air culture was also performed.


RESULTS
Cell population doubling time was ~10 h under continuous illumination without CO2enrichment, and large amounts of triacylglycerols (TAG) and fucoxanthin accumulated under a wide range of salinity and nutrient conditions, reaching ~200 and 18.5 mg/L, respectively. It was also shown thatC. gracilisproduced high amounts of TAG without the need for nitrogen or silica deprivation, which is frequently imposed to induce lipid production in many other microalgae. Furthermore,C. graciliswas confirmed to be highly tolerant to changes in environmental conditions, such as salinity. The diatom grew well and produced abundant lipids when using sewage water or liquid fertilizer derived from cattle feces without augmented carbon dioxide. High growth rates (doubling time <20 h) were obtained in a large-scale, open-air culture, in which light irradiance and temperature fluctuated and were largely different from laboratory conditions.


CONCLUSIONS
The ability of this microalga to accumulate TAG without nutrient deprivation, which incurs added labor, high costs, and complicates scalability, is important for low-cost industrial applications. Furthermore, its high tolerance to changes in environmental conditions and high growth rates observed in large-scale, open-air culture implied scalability of this diatom for industrial applications. Therefore,C. graciliswould have great potential as a biofactory.
Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Ako-gun, Hyogo 678-1297 Japan.
Hiromi
H
Tokushima
Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Ako-gun, Hyogo 678-1297 Japan.
Natsuko
N
Inoue-Kashino
Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Ako-gun, Hyogo 678-1297 Japan.
Yukine
Y
Nakazato
Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Ako-gun, Hyogo 678-1297 Japan ; Yanmar Environmental Sustainability Support Association, Umeda Gate-Tower, 1-9 Tsuruno, Kita-ku, Osaka, 530-8311 Japan ; College of Agriculture, Tamagawa University, 6-1-1 Tamagawagakuen, Machida, Tokyo, 194-8610 Japan.
Atsunori
A
Masuda
Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502 Japan.
Kentaro
K
Ifuku
Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Ako-gun, Hyogo 678-1297 Japan.
Yasuhiro
0000-0002-4278-9359
Y
Kashino
Biofuel; Chaetoceros gracilis; Chlorophyll; Diatom; EPA; Fucoxanthin; Lipid; Triacylglycerols