AUTO‐, HETERO‐, AND MIXOTROPHIC GROWTH OF CHLAMYDOMONAS HUMICOLA (CMLOROIMIYCKAK) ON ACETATE1

Abstract

ABSTRACTRelative growth rate, isocitrate lyase activity, chlorophyll, protein, lipid, and soluble carbohydrate contents were investigated in Chlamydomonas humicola Lucksch during auto‐, mixo‐, and heterotrnphic growth. Mixotrophic cells have a relative growth rate of 1.66 d –1as compared to 0.78 d –1 and 0.21 d –1 for hetero‐ and autotrophic cells, respectively. Addition of acetate to autotrophic cells resulted in an increase in cell dry weight during the first day, followed by a rapid decrease and stabilization at 40 pg·cell –1. Cellular yield of mixotrophu cells, on a dry weight basis, was 6.6 times that of heterotrophic cells and 21.9 limes that of autotrophic ones. After 4 d, mixotrophic cells were characterized by higher chlorophyll (3.6% dry weight [d.w.]) and protein (58.6% d.w.) contents and lower lipid (4.8% d.w.) and soluble carbohydrate (1.3% d.w.) contents than those of autotrophic (2.6% d.w. chlorophyll, 31.0% d.w. protein, 10.2% d.w. lipid, and 6.5% d.w. soluble carbohydrate) and heterotrophic (1.5% d.w. chlorophyll, 36.9% d.w. protein, 5.6% d.w. lipid, and 6.0% d.w. soluble carbohydrate) cells. The ratio of chlorophyll a/b was highest in heterotrophic cells due to lower chlorophyll b content. Isocitrate lyase activity, a key enzyme in ecetate assimitation, could not be detected in autotrophic cells. Addition of 10 mM acetate to the culture medium of hetero‐ and mixotrophic cells resulted in increased isocitrate lyase activity with a maximum after 24 h, followed by a decline in activity over a 7‐d period. After 7 d of growth, only 0.01 mM acetate was found in the culture medium of mixotrophic cells as compared to 3.2 mM in the medium of heterotrophic ones, from an initial concentration of 10 mM.