Multiple-stressor design-of-experiment (DOE) and one-factor-at-a-time (OFAT) observations defining Heterosigma akashiwo growth and cell permeability

Abstract

Heterosigma akashiwo is a cosmopolitan, fish-killing raphidophyte with blooms persisting from weeks to months in duration and extended periods of absence in coastal areas. Bloom initiation remains a conundrum, with environmental factors such as salinity, light, and temperature commonly considered the drivers. A common procedure to investigate the effect of these environmental factors on the growth of H. akashiwo is to use one-factor-at-a-time (OFAT) approach where only one factor is changed at a time while keeping others fixed. In this study, the design-of-experiment (DOE) approach, which is more efficient and accurate when examining the impact of two or more factors on a response, was used. The effect of these factors on the growth rate, doublings per day, yield, and cell membrane permeability of H. akashiwo (NWFSC-513) was determined to discover the optimum condition via a central composite design. Then, the effect of these factors was quantified, and a model for each response was computed to predict these reactions under the selected environmental conditions. Numerical optimization was used, and the models were confirmed through additional experiments and via analysis of variance (ANOVA). It was found that the maximum growth rate and doublings per day were detected at 25 °C, a salinity of 20.5, and light intensity of 200 μmol photons m⁻² s⁻¹. The highest yield (cells mL⁻¹) was observed at a temperature of 25 °C, a salinity of 30, and light intensity of 250 μmol photons m⁻² s⁻¹. Cell permeability, a strong positive correlate to cytotoxicity, was maximum when conditions were at the lower extremes (15 °C, a salinity of 5, and light intensity of 30 μmol photons m⁻² s⁻¹).