GLUCOSE TRANSPORT SYSTEMS AND GROWTH CHARACTERISTICS OF BRACTEACOCCUS MINOR1,2

Bracteacoccus minor grows on glucose both in the dark and in the light. However, the growth rates at 50 ft-c or higher in the presence of glucose are considerably lower than those in inorganic media at the same intensities. The lowered growth rates in the presence of glucose appear to be related to changes in metabolism toward increased production of storage carbohydrates. Glucose shortens the length of the lag phase at high light intensities and increases the length of the exponential phase at all light intensities, resulting in very high cell yields compared to cultures grown in inorganic media. B. minor has 2 transport systems for glucose: (1) a high affinity system, K_S=1 × 10^?5 M, which is formed in the dark in the absence of external glucose; and (2) a low affinity system, K_S=5 × 10^?4 M, which appears to be constitutive. At high concentrations of glucose there is also significant free diffusion of glucose into the cells. The glucose analog, 3-O-methyl glucose, is also taken up by the inducible system, but at a lower rate than glucose. It is Acumulated, about 2000 times in a 20-min incubation period, indicating active transport. Cycloheximide inactivates the high affinity system to the same extent as high light intensities, and also prevents induction of this system in the dark. Rates of photosynthesis are inversely correlated to glucose uptake rates over a range of light intensities of pre-incubation. The possession of a light-regulated high-affinity transport system as well as a constitutive low-affinity system for glucose is probably of competitive advantage to this alga in the soil environment.