O-031. Oxidative-Stress-Induced Metabolite Production with Sonocatalytic Formation of Reactive Oxygen Species

T. Katsuda1, C. Ogino1, H. Iwasaki1, K. Yamagami1, S. Katoh1, N. Shimizu2;
1Kobe Univ., Kobe, JAPAN, 2Kanazawa Univ., Kanazawa, JAPAN.

Background: Astaxanthin, a natural antioxidant, is produced by Haematococcus pluvialis along with the morphological change from the vegetative to cyst cell, and this change can be induced with reactive oxygen species (ROS). Previously, we found that the supplementation of TiO2 enhanced to form ROS in the aqueous media with the irradiation of ultrasounds. For the fermentative application of ROS formation with TiO2, ultrasounds are favorable stimuli because their attenuation behavior in suspension culture of microorganisms is much milder than that of ultraviolet light. In the present study, we applied TiO2 and ultrasounds to burden the ROS stresses onto the vegetative cells of H. pluvialis and induce the astaxanthin biosynthesis. Methods: The green alga H. pluvialis NIES 144 was grown at 20°C in 50 mL working volume of Kobayashi’s basal medium for 4 days under the illumination with fluorescent lamps. The cells were transferred to the fresh medium with the pellets of rutile type TiO2 (200 g L-1). The 42 kHz ultrasound was irradiated to the culture for 15 min at the sound pressure of 4.7 kPa in the water bath kept at 20 °C, and then the culture was incubated same as before after TiO2 pellets were removed. Results: After the ultrasound irradiation, H. pluvialis started to accumulate astaxanthin faster than the control experiment where the ultrasound was not irradiated to the culture: The production rate and the final concentration of astaxanthin in the ultrasound-irradiated experiment increased by 30% and 10%, respectively, while cell growth behaviors were same. On the other hand, we confirmed that the above ultrasound irradiation condition with TiO2 pellets oxidized methylene blue at the rate of 0.18 µM min-1. Conclusion: The ultrasound irradiation to the culture with TiO2 pellets accelerated the induction of astaxanthin accumulation in H. pluvialis by the formation of ROS, and this ROS formation method seemed suitable and advantageous for the industrial fermentative production of oxidative-stress-induced metabolite Production such as astaxanthin.