Effects of pH shift and agitation speed on chlorophyll biosynthesis in heterotrophic culture of Chlorella

Chlorella sp., which has been used for industrial biomass production, was c ultured under a heterotrophic condition. When pH was kept at 6.0 during the initial period of the culture, corresponding to logarithmic growth of cell , and thereafter shifted to 8.0, the instantaneous specific production rate s of chlorophyll(CHL! throughout the culture were maintained at relatively high values. This pH shift pattern was proposed as the optimum one. The max imum CHL content under the optimum pH shift, however, was only 1.28 W/W % a t the agitation speed of 600 r.p.m.. On the other hand, low agitation speed s less than 300 r.p.m. were more favorable for CHL biosynthesis. The maximu m CHL content reached 3.1 W/W % at the agitation speed of 250 r.p.m.. This value was about 2.4 times higher than that in the case of 600 r.p.m.. It wa s suggested that the effect of agitation speed on CHL biosynthesis depended on the existence of a period lacking oxygen supply. Though the maximum CHL content reached also about 3 W/W % under the constant pH value of 6.0 at a gitation speed of 250 r.p.m., the specific production rate of CHL during th e middle period of the culture was 0.54x10(-3) kg/ (kg dry cell.h), and abo ut 70 % of that in the case of the optimum pH shift. This result revealed t hat CHL biosynthesis in the heterotrophic culture of Chlorella sp, was carr ied out more efficiently under both the optimum pH shift and the agitation speed of 250 r.p.m..