The effects of growth conditions on the elemental and biochemical composition of the diatom Thalassiosira weissflogii and the haptophyte Emiliania huxleyi

A change in environmental conditions often leads to changes of physiology and biochemical composition of microalgae. Temperature and light intensity are important environmental factors regulating the growth of microalgae. In this study, the elemental and biochemical composition were measured in 2 marine microalgae under different temperatures and light intensities in nutrient replete and deplete conditions. The effect of temperature was observed in the marine haptophyte Emiliania huxleyi (CCMP 1516) at nutrient replete semi-continuous cultures. Triplicate cultures were incubated different temperature from 14 to 22oC and under photon flux densities (PFD) 600 μmol photons m−2 s−1. The growth rate (GR) of E. huxleyi increased with temperature. Cell volume varied with temperature, being about 40% smaller at higher temperature (22oC). Cellular chlorophyll a (chl a), nitrogen, phosphorus, and carbon contents were also lower at 22oC than other temperatures. Protein, total amino acids from free and combined amino acid, and total pigments [mol accessory pigment (mol chl a)-1] were decreased with increasing temperature; however, the opposite response was observed in fatty acids. In addition to the effect of combined temperature and light intensity was investigated in the marine diatom Thalassiosira weissflogii (CCMP 1056) under nutrient-limited semi-continuous cultures. The cultures were incubated at 16 and 26°C and PFD of 50 ± 10 (low light; LL) and 500 ± 10 (high light; HL) μmol photons m−2 s−1. HL incubated-cultures were diluted at 50% day-1 and LL incubated-cultures were diluted at 25% day-1. The GR were largely set by dilution rate (nitrogen limitation), but not by temperature and irradiance. The GR were around 0.72 d-1 in HL placed-cultures and 0.32 d-1 in the LL placed-cultures. Temperature did not affect mean cell size, whereas mean cell size decreased with increased irradiance by 20 to 29 %. Both temperature and irradiance influenced cellular chl a, carbon and chl a specific light absorption. Cellular nitrogen and phosphorus varied with temperature and irradiance. Protein, total amino acid (free and combined amino acid) and total fatty acid increased with increased temperature and irradiance; however, the opposite response was found in carbohydrate. Overall, temperature and light affected elemental and biochemical composition in 2 marine microalgae. Both relationship of the chlorophyll (chl):carbon (C) and RNA:protein ratio and growth rate in E. huxleyi under variable temperature positively supported a bio-optical and growth rate hypothesis respectively. However, the opposite response was found in T. weissflogii. Instead the C:chl and RNA:protein ratio and growth rate in T. weissflogii under variable irradiance positively supported a bio-optical and growth rate hypothesis.