Inhibition of the growth of the red microalga Porphyridium sp. by limitation of nutrient transfer

The unicellular red alga Porphyridium sp. was cultured in a medium to which increasing concentrations of its cell wall polysaccharide were added. As the polysaccharide concentration in the culture medium increased, algal growth rate and maximum cell number progressively decreased. In a different series of experiments it was shown that the polysaccharide also inhibited the rate of carbon uptake by the cells and as a result photosynthesis was also inhibited. In‐vitro experiments showed that the mass transfer coefficient for nitrate, bicarbonate, phosphate and potassium decreased as the polysaccharide concentration increased. The data indicate that the polysaccharide inhibits nutrient transfer from the medium to the cells, resulting in a reduction of the growth rate.