Influence of Carbon Sources on the Phenolic Compound Production by Euglena gracilis Using an Untargeted Metabolomic Approach

Abstract

Industrial development and urbanization has led to the diverse presence of metals in wastewater that are often improperly treated. The microalgae Euglena gracilis can tolerate high concentrations of metal via the excretion of organic metabolites, including phenolics. This study aims to evaluate how carbon amendment stimulates phenolic compound production by E. gracilis. The number, relative intensity and molecular composition of the phenolic compounds were significantly different between each of four carbon amended cultures (i.e., glutamic acid, malic acid, glucose, reduced glutathione) during the log phase. Phenolic compounds were mainly produced during the minimum growth rate, likely a response to stressful conditions. A better understanding of phenolic compounds production by E. gracilis and the impact of growth conditions will help identify conditions that favor certain phenolic compounds for dietary and metal chelation applications.

Keywords: Folin–Ciocalteu method; euglenoids; glutamic acid; metabolites; polyphenol.

Figure 1

Growth curve and the different phases with (A) glutamic acid, (B) glucose, (C) malic acid and (D) GSH amendment during lag (yellow), log (green), and stationary phases (red).

Figure 2

Mean reducing compound concentrations measured in the amended cultures (glutamic acid, glucose, malic and GSH) over the log phase. Different superscript letters indicate significant differences (p < 0.05) as determined by Wilcoxon test.

Figure 3

Cellular growth curve (black), number of molecular formulas (blue) and their relative intensities (red) attributed during the log phase with (A,E) glutamic acid, (B,F) glucose, (C,G) malic acid and (D,H) GSH amendment. The lag, log and stationary phases are shown in yellow, green and orange, respectively.

Figure 4

Elemental composition of phenolic compounds associated with (A) the minimum and (B) maximum growth rates. Different superscript letters indicate significant differences (p < 0.05) determined by Wilcoxon test.