Screening of the Two Pseudochloris wilhelmii Strains (Adriatic SAG 55.87 and Mangrove SAG 1.80) Cultured Under a Wide Range of Conditions: Nitrogen Concentration, Nitrogen Source and Salinity

The growth of two strains of Pseudochloris wilhelmii, Adriatic strain SAG 55.87 and Mangrove strain SAG 1.80, is compared under different salinities, nitrogen sources and concentrations by a fast 96-well screening method. Cultures were grown in BG11 medium with modifications of nitrogen source (ammonium and nitrate) and nitrogen concentrations (0.3 to 19.2 mM) across salinities ranging from 2 to 24 PSU. Growth was measured by optical density at 690 nm, and specific growth rates were analyzed using a Bayesian generalized additive mixed model to identify optimal conditions. Both strains tolerate a broad range of salinities, but cell density was generally higher with nitrate as a nitrogen source than with ammonium nitrogen. The Adriatic strain showed better growth performance when grown on nitrate, with a mean observed growth rate of 0.143 d−1 and a 1.96-fold increase in OD690. The Mangrove strain showed narrower response and lower mean growth rates on nitrate (0.104 d−1). Overall, both strains showed similar growth performance on ammonium, with comparable mean growth rates of 0.0304 for the Adriatic strain and 0.0358 for the Mangrove strain. The results show high intraspecific variation in tolerance to salinity and nitrogen for P. wilhelmii. This 96-well screening method for microalgae cultivation is a powerful and rapid tool for narrowing down optimal growth conditions, as well as to be used as a guide for a larger-scale setup.