Accumulation of docosahexaenoic acid-rich lipid in thraustochytrid Aurantiochytrium sp. strain T66: effects of N and P starvation and O2 limitation

Abstract

Aurantiochytrium sp. strain T66 was grown in batch bioreactor cultures in a defined glutamate- and glycerol-containing growth medium. Exponentially growing cells had a lipid content of 13% (w/w) of dry weight. A fattening of cells fed excess glycerol occurred in the post-exponential growth phase, after the medium was depleted of N or P. Lipid accumulation was also initiated by O2 limitation (below 1% of saturation). N starvation per se, or in combination with O2 limitation, gave the highest lipid content, i.e., 54% to 63% (w/w) of dry weight. The corresponding maximum culture density was 90 to 100 g/l dry biomass. The content of docosahexaenoic acid (22:6n-3) in N starved, well-oxygenated cells reached 29% (w/w) of total fatty acids but increased to 36% to 52% in O2-limited cells, depending on the time span of the limitation. O2-limited cells did not accumulate the monounsaturated fatty acids that were normally present. We inferred that the biological explanation is that O2 limitation hindered the O2-dependent desaturase(s) and favored the O2-independent polyunsaturated fatty acid synthase. The highest overall volumetric productivity of docosahexaenoic acid observed was 93 mg/l/h. Additionally, we present a protocol for quantitative lipid extraction, involving heat and protease treatment of freeze-dried thraustochytrids.

Detection of Genes Involved in Fatty Acid Elongation and Desaturation in Thraustochytrid Marine Eukaryotes

“…The DHA content in these species commonly reaches 50 of their total fatty acids 17,22 . In this study, similarly higher DHA contents were also observed in T. aureum and T. roseum, in which they were much higher than those in all of the other strains T. striatum and Schizochytrium spp.…”

Reactive Oxygen Species-Mediated Cellular Stress Response and Lipid Accumulation in Oleaginous Microorganisms: The State of the Art and Future Perspectives

“…For example, Duan et al (2012) reported that Chlorella vulgaris experienced a 21.1% increase of lipid yield when exposed to salt pressure. Biosynthesis of lipids is also induced by other physical environmental stresses, such as low oxygen in the microalga Aurantiochytrium sp., and dehydration in the green alga Chlorella kessleri (Jakobsen et al, 2008; Shiratake et al, 2013). …”

Microbial lipid production by Rhodosporidium toruloides under sulfate-limited conditions

“…Very recently, it has also been suggested as a potential feedstock for biodiesel industry (Adamczak et al, 2009;Easterling et al, 2009;Li et al, 2008;Vicente et al, 2010), because microbial lipid can be produced using various cheap feedstocks, especially renewable biomaterials such as lignocelluloses. Early studies suggested that oleaginous microorganisms should be cultivated for lipid accumulation in the media with excess carbon sources and one particular limiting element such as nitrogen, phosphorus, zinc, iron or magnesium (Gill et al, 1977;Jakobsen et al, 2008). Thus, when the limiting nutrient was exhausted, cell growth was repressed and the remaining carbon source was converted to storage lipid.…”