Variations in the biochemical composition of the diatom Coscinodiscus eccentricus with culture age and salinity

Abstract

Cultures of the marine diatom Coscinodiscus eccentricus Ehrenberg were grown at four salinities, namely 20, 25, 30 and 35%. The changes in the carbohydrate, protein, silicon and pigment concentrations of the cells were studied throughout the growth cycles in these salinities. The carbohydrate content, expressed as a percentage of the cell dry weight, increased in all cultures during the lag and early log phases. It later fell, sharply at first, as it was used up faster than it was produced. It was not stored during the stationary phase. The protein percentage composition built up to a peak at different stages during the exponential or stationary growth stages, depending on the salinity, but was later respired. The silicon percentage of the dry weight usually decreased during the log phase, as the cells were dividing before becoming fully silicified, and remained low in the stationary phase due to an increase in the volume of the cells. The changes in the frustular thickness were also calculated. The values ranged from 0.24 to 0.35 μm (at the beginning and end of the experiments) to 0.15 μm during the log growth phase. The pigment content was always low. The lipid composition of the cells was calculated by difference. It was usually low during the exponential growth phase, but was accumulated during the stationary phase. The point at which this accumulation began was associated with the time when protein respiration started.