CARBON-DIOXIDE FIXATION AND ALPHA-LINOLENIC ACID PRODUCTION BY THE HOT-SPRING ALGA CYANIDIUM-CALDARIUM

Focusing on CO2 fixation and alpha-linolenic acid (ALA) production, photoautotrophic cultivation of the hot-spring alga Cyanidium caldarium was investigated using Allen's medium under a 5 % CO2-enriched atmosphere. Although the growth rate was maximum at ca. 40-degrees-C, the optimum cultivation conditions (temperature, H+ concentration in the medium and light intensity) for ALA production were found to be 30-degrees-C, pH 2.0-4.0 and ca. 10,000 lux respectively. Simulation of a chemostat cultivation at these optimum conditions showed that the rates of CO2 fixation and of ALA production could reach 0.75 kg-CO2/(kg-cells.d) and 5.44 g-ALA/(kg-cells.d), respectively, in the exponential phase. This rate of CO2 fixation corresponded to 0.030 kg-CO2/(m3.h) at a cell concentration of 0.96 kg/m3. This activity of C. caldarium for CO2 fixation was comparable to that of blue-green algae and was 10 to 100 times greater than that of green plants. Thus, C. caldarium was shown to be useful for the fixation of CO2.