Ｃｈｌｏｒｅｌｌａ ｓｐ（Ｃｓ）の増殖特性，特にＢ．ｍｅｇａｔｅｒｉｕｍ（Ｂｍ）との共生による増殖

Abstract

Growth characteristics of Chlorella sp. isolated from a sedimentation tank in glycine, glucose and inorganic medium and also in peptone medium in association with B. megaterium were discussed. Chlorella sp. utilized glycine phototrophycally and specific growth rate (μ) was 3.35 day-1 (25°C). The isolate also utilized small amount of glycine heterotrophycally (under dark and the supply of air) and specific growth rate (μ) was 2.76 day-1. The isolate utilized glucose heterotrophycally (μ= 2.70 day-1). Under the supply of CO2 enriched air to the inorganic medium, specific growth rate of 3.30 day was obtained at more than 0.6% CO2 concentration. Although the isolate showed a little growth in 0.5% peptone medium, it grew promptly when it was incubated in association with B. megaterium. This symbiotical growth took place under light and oxygen limited conditions (μ=4.50 day-1, 2°C). No growth of Chlorella sp. was observed under an aerobic condition. Growth rate of the isolate was accelerated with an increase of temperature and reached to the maximum μ of 8.0 day-1 at 36°C. Rapid growth was still observed at 42°C. But, this high growth rate continued only for 12 hrs. In 0.1% glycine medium, the maximum growth rate without bacteria was observed at 30°C., and growth was completely ceased above 40°C. Carbon analysis before and after incubation indicated that organic carbon degraded by the bacterium quantitatively transferred to the biomass. This symbiotical growth was also observed in simple organic medium in which B. megaterium could grow. From these results, it was assumed that the symbiosis observed between B. megaterium and Chlorella sp. fundamentaly consisted of interchange of CO2 and O2. But, high growth rate observed in symbiosis might indicate the existence of more complicated mechanisms supporting each other.