Hirotaka Kakita1, Naoki Yanaoka1, Hideki Obika2
1Graduate School of Integrated Basic Sciences, Nihon University, Tokyo, 156-8550, Japan
2Health Research Institute, National Institute of Advanced Industrial Science and Technology, Kagawa, 761-0301, Japan
Interactions between macro algae and attached bacteria have been reported to date. The attached bacteria use the organic compounds secreted by macro algae as sources of nutrition. Some macro algae assimilates vitamins and phytohormones, such as indole-3-aceticacid (IAA), produced by bacteria for algal growth. On the other hand, Japanese species of the red algal family Gracilariaceae are important industrial macro algae, because they have been harvested in Japan as commercial sources of agar and for food additives. They also produce bioactive substances such as enzymes and hemagglutinins. However, details of the environmental bacteria on Japanese Gracilariaceae have never been reported on. Thus, in this study, we investigated the effects of a bacterial auxin, IAA, on algal growth of three kinds of Japanese algal family Gracilariaceae, Gracilaria vermiculophylla, Gracilaria blodgettii, and Gracilariopsis chorda. The effects of IAA on algal components such as sugars, proteins, carotenes were also investigated. Algal components were determined by colorimetric assay and high performance liquid chromatography. Algal apical fragments (each 5 mm length) were cultured in IAA-free medium for 2 weeks and then transferred to various concentrations of IAA-added medium to compare the algal growth rate. Among three Gracilariaceae species tested, the acceleration of algal growth rate by IAA addition was greatest in G. chorda. These findings suggest that IAA seems to be useful as an algal growth accelerator