Stress-Induced Production of Bioactive Oxylipins in Marine Microalgae

Abstract

Microalgae, stemming from a complex evolutionary lineage, possess a metabolic composition influenced by their evolutionary journey. They have the capacity to generate diverse polyunsaturated fatty acids (PUFAs), akin to those found in terrestrial plants and oily fish. Also, because of their numerous double bonds, these metabolic compounds are prone to oxidation processes, leading to the creation of valuable bioactive molecules called oxylipins. Moreover, owing to their adaptability across various environments, microalgae offer an intriguing avenue for biosynthesizing these compounds. Thus, modifying the culture conditions could potentially impact the profiles of oxylipins. Indeed, the accumulation of oxylipins in microalgae is subject to the influence of growth conditions, nutrient availability, and stressors, and adjusting these factors can enhance their production in microalgae culture. Consequently, the present study scrutinized the LC-MS/MS profiles of oxylipins from three marine microalgae species (two Haptagophytes and one Chlorophyte) cultivated in 1 L of photobioreactors under varying stress-inducing conditions, such as the introduction of H₂O₂, EtOAc, and NaCl, during their exponential growth phase. Approximately 50 oxylipins were identified, exhibiting different concentrations depending on the species and growth circumstances. This research suggests that microalgae metabolisms can be steered toward the production of bioactive oxylipins through modifications in the culture conditions. In this instance, the application of a low dose of hydrogen peroxide to Mi 124 appears to stimulate the production of nonenzymatic oxylipins. For Mi136, it is the application of salt stress that seems to increase the overall production of oxylipins. In the case of Mi 168, either a low concentration of H₂O₂ or a high concentration of AcOEt appears to have this effect.

Keywords: LC-MS/MS; microalgae; osmotic stress; oxidative stress; oxylipins.

Figure 1

Enzymatic and nonenzymatic pathways of omega-3 and omega-6 PUFAs and their oxygenated derivatives in marine microalgae. Linoleic acid (LA), alpha-linolenic acid (ALA), arachidonic acid (ARA), eicosapentaenoic acid (EPA), docosapentanoic acid (DPA), docosahexaenoic acid (DHA), lipoxygenase (LOX), cytochrome (CYP), cyclooxygenase (COX), hydroxyoctadecadienoic acids (HODEs), prostagladines (PGs), thromboxanes (TxBs), epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraenoic acids (HETEs), lipoxins A (LxAs), hydroxyeicosapentaenoic acid (HEPEs), resolvins Es (RvE), resolvins Ds (RvD), hydroxydocosahexaenoic acid (HDHA), protectins Ds (PDs), phytoprostanes (PhytoPs), phytofurans (PhytoFs), isoprostanes (IsoPs), and neuroprostanes (NeuroP).

Figure 2

Sums of the concentrations, expressed in pg/mg DWB, of oxygenated metabolites classified by PUFAs in Mi124 depending on growing conditions: control condition versus stress-inducing conditions (H₂O₂ at 1 mM or 4 mM; EtOAc at 0.5 or 1 mM; and NaCl at 45 g/L).

Figure 3

Sums of the concentrations, expressed in pg/mg DWB, of oxygenated metabolites classified by PUFAs in Mi136 depending on the growing conditions; control condition versus stress-inducing conditions (H₂O₂ at 1 mM or 5 mM; EtOAc at 4 or 10 mM; and NaCl at 45 g/L).

Figure 4

Sums of the concentrations, expressed in pg/mg DWB, of oxygenated metabolites classified by PUFAs in Mi168 depending on the growing conditions; control condition versus stress-inducing conditions (H₂O₂ at 0.25 mM or 1 mM; EtOAc at 2 or 10 mM; and NaCl at 29 g/L or 45 g/L).

Figure 5

Experimental design of the stress inductions (+: Low dose; ++: high dose).