Paris Paredes

Oblongichytrium RT2316-13 synthesizes lipids rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The content of these fatty acids in the total lipids depended on growth temperature. Sequencing technology was used in this work to examine the thraustochytrid’s response to a decrease in growth temperature from 15 °C to 5 °C. Around 4% (2944) of the genes were differentially expressed (DE) and only a few of the DE genes (533 upregulated; 206 downregulated) had significant matches to those in the SwissProt database. Most of the annotated DE genes were related to cell membrane composition (fatty acids, sterols, phosphatidylinositol), the membrane enzymes linked to cell energetics, and membrane structure (cytoskeletal proteins and enzymes). In RT2316-13, the synthesis of long-chain polyunsaturated fatty acids occurred through ω3- and ω6-pathways. Enzymes of the alternative pathways (Δ8-desaturase and Δ9-elongase) were also expressed. The upregulation of the genes coding for a Δ5-desaturase and a Δ5-elongase involved in the synthesis of EPA and DHA, explained the enrichment of total lipid with these two long-chain fatty acids at the low temperature. This molecular response has the potential to be used for producing microbial lipids with a fatty acids profile similar to that of fish oils.

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.

Thraustochytrids have been isolated from different aquatic systems; however, few studies have reported their occurrence in Antarctica. In this study, 13 strains close to strains belonging to the genera Oblongichytrium, Thraustochytrium, and Aurantiochytrium were isolated from seawater samples collected near the Antarctic Base Professor Julio Escudero (S 62°12′57′ E 58°57′35″). Docosahexaenoic acid (DHA) was found in the total lipids of all the isolates; DHA content of the biomass (dry weight) varied between 3.3 and 33 mg/g under the growth conditions for isolation. Five of the Antarctic thraustochytrids were able to accumulate lipids at levels higher than 20% w/w. Two strains, RT2316‐7 and RT2316‐13, were selected to test the effect of the incubation temperature (at 5°C for 14 days and at 15°C for 5 days). Incubation temperature had little effect on the lipid content and biomass yield; however, its effect on the fatty acid composition was significant (p < .05). The low incubation temperature favored the accumulation of eicosapentaenoic acid (EPA), palmitic acid and stearic acid in the total lipids of RT2316‐7. Percentage of EPA, DHA and the omega‐6 fatty acid dihomo‐γ‐linolenic acid of total fatty acids of RT2316‐13 was higher at the low incubation temperature. RT2316‐13 accumulated the highest lipid content (30.0 ± 0.5%) with a carbon to nitrogen mass ratio equal to 16.9. On the contrary, lipid accumulation in RT2316‐7 occurred at high concentration of the nitrogen sources (monosodium glutamate or yeast extract). The capability to accumulate lipids with a fatty acid profile that can be tuned through cultivation temperature make the Antarctic thraustochytrid RT2316‐13 a candidate for the production of lipids with different uses.