Hybrid photobioreactor operation for the intensified production of Haslea ostrearia and marennine in function of strain variability

Abstract

Marennine is a high-value compound produced by the benthic diatom Haslea ostrearia, which could be used as an alternative to synthetic antibiotics in aquaculture. Over the last few years, however, low production rates have been impeding its exploitation. Recent progress on H. ostrearia culture devices led to the design of a particular photobioreactor (PBR) for high yield marennine production, which remained to be further studied: the objective of this study is thus to evaluate the advantages of using a submerged membrane photobioreactor (MPBR) for the culture of H. ostrearia by testing the reliability of its performances when changing strains. In addition, the impact of the decrease in cell size through time, as experienced by H. ostrearia along its life cycle, was studied in regard to marennine productivity, thus considering inter- and intra-strain variability. Using the 1 L MPBR proposed by Gargouch et al. (2022) three different strains of H. ostrearia were cultivated in a fed-batch mode and marennine was collected in a semicontinuous way (D = 0,1 d−1) with an ultrafiltration membrane immersed in the culture. Biometrics of the inocula were measured, and biomass development and marennine production were followed over 20 days of culture. Results confirmed the advantage brought by the addition of a membrane inside the culture chamber enabling to maintain a minimal productivity of 2 mg d−1, using only 3 L of fresh culture medium over a 20-day culture. Results also showed that cell downsizing along H. ostrearia life cycle did impact marennine productivity per cell, with smaller cells (i.e. older strains), displaying a 4 to 15 times increase in biovolumetric marennine productivity depending on the strain. Hypotheses explaining this increase in marennine production along the life cycle of H. ostrearia are discussed, considering also changes in the microbiome or epigenetic variations along strain life cycle.