Growth and biochemical variability of the marine microalga Chlorella stigmatophora in batch cultures with different salinities and nutrient gradient concentration

Abstract

[Abstract] Chlorella stigmatophora was cultured under 56 different combinations of nutrient-salinity concentrations, ranging from 1 to 64 mM NaNO3 and from 0 to 35%. salinity. Optimal growth conditions for obtaining maximum cellular densities were between 1 and 8 mM NaNO3 for any salinity, with a maximum growth rate at the logarithmic phase of 0·51 doublings d-1. Production over the 15 days as measured by chlorophyll a estimation were maximal between 5 and 20%. and 8–32 mM NaNO3. Maximum protein per ml occurred at 8 and 16 mM NaNO3 for all the salinities, whereas maximum protein/cell contents were obtained at 16 and 32 mM NaNO3. Protein content per ml and per cell was not affected by salinity. The nitrate/protein transformation rate is related to nitrate concentration. Maximum rates were obtained at 1 mM NaNO3, with values between 92% and 100%. Nutrient concentration produced changes in the biomass production and biochemical composition of this marine microalga, with wide variations in the chlorophyll a and protein content per ml (up to 700% and 500%, respectively). This microalga shows an important capacity to adapt to changes in salinity, ranging from freshwater (0%.) to oceanic sea-water (35%.). The significance of these results for the possible utilization of Ch. stigmatophora as source of Single Cell Protein (SCP) is discussed.