Physiological Adaptation of Chromochloris zofingiensis in Three-Phased Cultivation Performed in a Pilot-Scale Photobioreactor

<i>Chromochloris zofingiensis</i> is a green alga that serves as a valuable source of lipids, proteins, and carotenoids. Compared to well-studied microalgal carotenoid producers, <i>C. zofingiensis</i> offers several advantages, including high biomass, lipid and carotenoid productivity as well as less susceptibility to contaminations. <i>C. zofingiensis</i> can achieve growth rates up to four times higher than those of <i>H. pluvialis</i> under optimal phototrophic conditions. Although several studies have examined its cultivation and carotenogenesis under different tropic growth modes at laboratory scale, few have focused on pilot-scale systems. The goal of this study is to investigate the microalga's physiological adaptation in a 200 L tubular photobioreactor during a three-phase semi-continuous cultivation strategy, particularly focusing on the changes in macromolecular and pigment composition. After an initial biomass accumulation phase, a two-phased stress phase was applied combining nutrient depletion (phase 1) and osmotic salt stress conditions (phase 2). Following this procedure, the cellular protein content dropped to 44.7% of its initial level, while the lipid content rose by up to 320%. Additionally, the astaxanthin concentration increased from 1.1 mg/g_DW to 4.9 mg/g_DW during the last osmotic stress phases, aligning with results from published laboratory-scale studies.