The chemical composition of Chaetoceros sp. (Bacillariophyceae) under different light conditions

Abstract

Chaetoceros sp. growth with white, pure blue and mixed blue light in 10-1 semicontinuous culture with 50% daily dilutions was light-limited at photon flux densities of 199 μmol m −2 s −1. At the above light level the type of light did not cause variations in protein content, but the use of mixed blue (192.5 μmol m −2 s −1 of blue, and 6.5 of white, light) caused an important decrease in carbohydrates and an increase in lipids. Chlorophyll a was higher in blue than in white light. Increasing photon flux densities increased biomass production. In white light photoinhibition occurred earlier than in blue light ( >498 and 565 μmol m −2 s −1, respectively). The highest cell densities were in white light, but the highest yields in biomass (mg l −1) were in mixed blue, due to the higher mean cell weight. There were no differences in chlorophyll content. The proximate composition of the biomass produced at saturating photon fluxes did not change considerably in white light. Both types of blue caused an increase in proteins but the alternative carbon sinks were lipids in mixed blue and carbohydrates in pure blue light. Methionine was highest in mixed blue and there were no other important differences in amino acid profiles. 18C fatty acids were greater than 24% in pure blue and less than 5% in white and mixed blue. The unsaturate 18:1 (oleic acid) was more than 15% of the total fatty acids in pure blue, which might have important effects on the dietary value of the biomass produced.