Interactions between Glucose and Inorganic Carbon Metabolism in Chlorella vulgaris Strain UAM 101

Abstract

Chlorella vulgaris strain UAM 101 has been isolated from the effluent of a sugar refinery. This alga requires glucose to achieve maximal growth rate even under light saturating conditions. The growth rate of cultures grown on light + CO(2) + glucose (3.16 per day) reaches the sum of those grown on light + CO(2) (1.95 per day) and on dark + glucose (1.20 per day). Unlike other Chlorella strains, uptake of glucose (about 2 micromoles per milligram dry weight per hour) was induced to the same extent in the light and dark and was not photosensitive. The rate of dark respiration was not affected by light and was strongly stimulated by the presence of glucose (up to about 40% in 4 hours). The rate of photosynthetic O(2) evolution was measured as a function of the CO(2) concentration. These experiments were conducted with cells which experienced different concentrations of CO(2) or glucose during growth. The maximal photosynthetic rate was inhibited severely by growing the cells in the presence of glucose. A rather small difference in the apparent photosynthetic affinity for extracellular inorganic carbon (from 10-30 micromolar) was found between cells grown under low and high CO(2). Growth with glucose induced a reduction in the apparent affinity (45 micromolar) even though cells had not been provided with CO(2). Experiments performed at different pH values indicate CO(2) as the major carbon species taken from the medium by Chlorella vulgaris UAM 101.