Temperature and irradiance impacts on the growth,pigmentation and photosystem II quantum yields of Haematococcus pluvialis (Chlorophyceae)

The microalga Haematococcus pluvialis Flotow has been the subject of a number of studies concerned with maximizing astaxanthin production for use in animal feeds and for human consumption. Several of these studies have specifically attempted to ascertain the optimal temperature and irradiance combination for growth of H. pluvialis, but there has been a great deal of disagreement between laboratories. “Ideal” levels of temperature and irradiance have been reported to range from 14 to 28°C and 30 to 200 μmol photons m⁻² s⁻¹. The objective of the present study was to simultaneously explore temperature and irradiance effects for a single strain of H. pluvialis (UTEX 2505) across an experimental region that encompassed the reported “optimal” combinations of these factors for multiple strains. To this end, a two-dimensional experimental design based on response surface methodology (RSM) was created. Maximum growth rates for UTEX 2505 were achieved at 27°C and 260 μmol photons m⁻² s⁻¹, while maximum quantum yield for stable charge separation at PSII (F_v/F_m) was achieved at 27°C and 80 μmol photons m⁻² s⁻¹. Maximum pigment concentrations correlated closely with maximum F_v/F_m. Numeric optimization of growth rate and F_v/F_m produced an optimal combination of 27°C and 250 μmol photons m⁻² s⁻¹. Polynomial models of the various response surfaces were validated with multiple points and were found to be very useful for predicting several H. pluvialis UTEX 2505 responses across the entire two-dimensional experimental design space.