Dynamic flux balance analysis of biomass and lipid production by Antarctic thraustochytrid Oblongichytrium sp. RT2316‐13

Abstract

Production of biomass and lipids in batch cultures of the Antarctic thraustochytrid Oblongichytrium sp. RT2316‐13, is reported. The microorganism proved capable of producing nearly 67% docosahexaenoic acid (DHA) and 15% eicosapentaenoic acid (EPA) in its total lipid fraction. Biomass with a maximum total lipid content of 33.5% (wt/wt) could be produced at 15°C in batch culture using a medium containing glucose (20 g/L), yeast extract (10.5 g/L), and other minor components. A lower culture temperature (5°C) reduced biomass and lipid productivities compared to culture at 15°C, but enhanced the DHA and EPA content of the lipids by 6.4‐ and 3.3‐fold, respectively. Both a simple minimally structured mathematical model and a more complex genome‐scale metabolic model (GEM) allowed the fermentation profiles in batch cultures to be satisfactorily simulated, but the GEM provided much greater insight in the biochemical and physiological phenomena underlying the observed behavior. Unlike the simpler model, the GEM could be interrogated for the possible effects of various external factors such as oxygen supply, on the expected outcomes. In silico predictions of oxygen effects were consistent with literature observations for DHA producing thraustochytrids.

High-quality genome-scale metabolic model ofAurantiochytriumsp. T66

“…The biomass composition was adapted from the neutral lipid-free biomass (Shene et al, 2020). Splitting the biomass into preceding precursor reactions, we formulated unique biomass reactions of the following categories: proteins, carbohydrates, DNA, RNA, unsaponifiable matter, polar lipids, and free fatty acids.…”

“…We also swapped each amino acid for their corresponding aminoacyl-tRNA and added additional energy carriers required for the process of translation. The total carbohydrate content was obtained from previous work (Shene et al, 2020), while the weight fractions was assumed to be the same as that of S. limacinum (C Ye et al, 2015). To estimate the energy requirements for the polymerization of these monomeric carbohydrates, we employed their corresponding nucleotide sugars.…”

“…We stoichiometrically weighted the components of each of the precursor reactions using appropriate correction factors and further scaled the precursors in the final biomass reaction using experimentally determined weight fractions (i.e. g component gDW -1 ) (Shene et al, 2020).…”

“…We also substituted the monomeric precursors with corresponding (deoxy)nucleoside triphosphates, simulating the energetic cost of replication and transcription, respectively. We used previously determined levels of unsaponifiable matter, polar lipids, and free fatty acids (Shene et al, 2020), while updating the fatty acyl distribution to that of T66 cells sampled during exponential growth. Lacking detailed experimental data on the quantitative levels of specific lipids of particular chain configurations, we further assumed that all lipid classes would have the same fractional acyl chain composition.…”

“…RT2316-13 (Shene et al, 2020). This biomass reaction is specifically tailored for exponentially growing cells where the lipid proportion is free of neutral lipids such as TAG, and predominately contains the polar lipids phosphatidylcholine and phosphatidylethanolamine.…”