Fatty acid and metabolomic profiling approaches differentiate heterotrophic and mixotrophic culture conditions in a microalgal food supplement 'Euglena'

Abstract

BackgroundMicroalgae have been recognized as a good food source of natural biologically active ingredients. Among them, the green microalga Euglena is a very promising food and nutritional supplements, providing high value-added poly-unsaturated fatty acids, paramylon and proteins. Different culture conditions could affect the chemical composition and food quality of microalgal cells. However, little information is available for distinguishing the different cellular changes especially the active ingredients including poly-saturated fatty acids and other metabolites under different culture conditions, such as light and dark.ResultsIn this study, together with fatty acid profiling, we applied a gas chromatography–mass spectrometry (GC-MS)-based metabolomics to differentiate hetrotrophic and mixotrophic culture conditions.ConclusionsThis study suggests metabolomics can shed light on understanding metabolomic changes under different culture conditions and provides a theoretical basis for industrial applications of microalgae, as food with better high-quality active ingredients.

Euglena gracilis growth and cell composition under different temperature, light and trophic conditions

“…gracilis contained up to five times more unsaturated fatty acids than the cells grown in the dark ( Fig 4b ). The same trend has also been observed by Schwarzhans et al [ 28 ] and Zeng et al [ 43 ].…”

“…In the current study, we provided 3 x 400 μmol m 2 s -1 and observed a delay of 8 days before glucose consumption started at 23 °C, reduced to only 4 days at 27 °C ( Fig 2 ). Although the specific growth rate in mixotrophic cultures was slightly lower than in heterotrophic cultures ( Table 3 ), the final biomass concentration was higher in the mixotrophic conditions, as observed by Yamane et al [ 42 ] and Zeng et al [ 43 ]. Providing light to the mixotrophic culture at 27 °C was sufficient to prevent cell death and lysis after glucose had been consumed.…”

“…to produce 39.6 g L -1 biomass [ 17 ]) conditions to generate high biomass concentrations. Although providing light incurs cost, mixotrophy remains of interest since specific products, such as unsaturated fatty acids, are only produced or are produced in larger amounts when cultures are exposed to light [ 42 , 43 , 45 ].…”

“…gracilis accumulates much less lipid than oleogenic microalgal species like Chlorella (30–57% lipid) [ 32 ] and Nannochloropsis (26–42% lipid) [ 46 ], but is known to contain a large proportion of unsaturated lipids [ 47 ]. Although lipid content as high as 37% has been reported from photoautotrophic conditions [ 48 ], the lipid content is typically only 8 to 18% of the cell biomass [ 43 , 44 ]. Neutral lipids are not the main storage compounds of E .…”

“…gracilis are found in chloroplast membranes [ 48 ] and the unsaturated fatty acid content of the cells is affected by the activity and amount of chloroplasts, which, in turn, are dependent on light availability. Up to 80% of the lipids in light grown cells may be unsaturated, while the proportion in dark grown cells was 32% [ 43 , 51 ]. In the current study, we observed 78 to 88% unsaturated fatty acids in cells grown in light and around 72% in cells grown without light.…”