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 + CO2 + glucose (3.16 per day) reaches the sum of those grown on light + CO2 (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 02 evolution was measured as a function of the CO2 concentration. These experiments were conducted with cells which experienced different concentrations of CO2 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 CO2. Growth with glucose induced a reduction in the apparent affinity (45 micromolar) even though cells had not been provided with CO2. Experiments performed at different pH values indicate CO2 as the major carbon species taken from the medium by Chlorella vulgaris UAM 101. We (9) have previously described the heterotrophic potential of the algal population from a sugar refinery wastewater environment. The most abundant alga in this habitat, Chlorella vulgaris UAM 101, exhibited a relatively low rate of growth when cultured photoautotrophically. Its growth rate, however, was strongly stimulated when the medium was supplemented with some of the organic compounds normally present in its habitat.The present paper reports the effect of light on the growth ofthis strain, as well as special characteristics ofglucose uptake and photosynthetic and respiratory performance in light that are related to the glucose stimulation of growth.
MATERIALS AND METHODS
OrganismChlorella vulgaris UAM 101 is a wild strain that we have isolated from the wastewater effluent of a sugar refinery '
Cyanobacterial mutants are being used to elucidate the processes involved in their ability to adapt to changes in the ambient concentration of CO,, including the operation of the Ci-concentrating mechanism. The latter enables the cells to grow in the presence of low concentrations of ambient CO, (for recent reviews, see Pierce and
Inactivation of ccmO in Synechococcus sp. strain PCC 7942 resulted in a mutant which possesses aberrant carboxysomes and a normal inorganic carbon uptake capability but a reduced ability to photosynthetically utilize the internal inorganic carbon pool. Consequently, it exhibits low apparent photosynthetic affinity for extracellular inorganic carbon and demands high levels of CO2 for growth.
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