Limited feeding of potassium nitrate for intracellular lipid and triglyceride accumulation of Nannochloris sp. UTEX LB1999

Abstract

Limited feeding of nitrate during culture of Nannochloris sp. UTEX LB1999 for intracellular lipid and triglyceride accumulation was investigated with the aim of obtaining cells superior for liquefaction into a fuel oil. The intracellular lipid contents and the percentage of triglycerides in the lipids of cells grown in a nitrogen-limited medium (0.9 mM KNO3) were 1.3 times as high as those grown in a modified NORO medium containing 2.0-9.9 mM KNO3. However, the cell concentration was too low for the practical production of fuel oil by high-pressure liquefaction of the cell mass. A single feeding of 0.9 mM nitrate after nitrate depletion during cultivation in a nitrate-limited medium increased the cell concentration to twice that obtained without such feeding, and the lipid content was maintained at a high level. The timing of nitrate feeding, i.e., whether it was given during the log phase (before nitrate depletion), the constant growth phase (just after the depletion), or the stationary phase (after the depletion), had negligible effect on the intracellular lipid content and percentage of triglycerides in the lipids. When 0.9 mM nitrate was intermittently fed ten times during the log phase in addition to the initial nitrate feed (0.9 mM), the cell concentration reached almost the same (2.16 g/l) and the intracellular lipid content and the percentage of triglycerides in the lipids increased from 31.0 to 50.9% and 26.0 to 47.6%, respectively, compared with those of cells cultured in a modified NORO medium containing 9.9 mM KNO3 without additional nitrate feeding.

Effects of Environmental Factors and Nutrient Availability on the Biochemical Composition of Algae for Biofuels Production: A Review

“…Inorganic nitrogen taken up by algae is rapidly assimilated into biochemically active compounds and recycled within cells to meet changing physiological needs [156,157]. Major effects of nitrogen deficiency in algal culture include the enhanced biosynthesis and accumulation of lipids [75,80,[158][159][160] and triglycerides [161,162] with a concomitant reduction in protein content [25,29,[163][164][165][166]. This, in turn, results in a higher lipid/protein ratio [80] at the expense of growth rate [167].…”

Protocol for maximizing the triglycerides-enriched lipids production from <i>Dunaliella salina</i> SA32007 biomass, isolated from the Salar de Atacama (Northern Chile)

“…It has been stated that, under nitrogen limitation, microalgae can activate protection mechanisms like the modification of lipid metabolism, since the diacilglicerolaciltransferase enzyme can turn it into acetyl CoA and TAGs [2,11,14,44]. Thus, microalgae would be able to generate reservoirs of neutral lipids in the form of TAGs, which could be stored for the reconstruction of chloroplast membranes or mainly as sources of carbon (CO 2 ) and energy [13].…”

“…Moreover, other limiting treatments (5/1 and 0.5/1), being able to stimulate the synthesis of lipids [14,43,44], suffered a severe physiological restriction, which prevented them to express such stimulation. Then, there exists a nitrogen limitation threshold under which the strain would not be able to increase the concentration of lipids due to a metabolic block [45].…”

“…Different culture tests including high salinity and nutrient limitation (e.g. Mg, K, Na, NO 3 and PO 4 ) can enhance lipid synthesis and particularly triglycerides, but unfortunately these conditions produced a microalgae biomass reduction and therefore, the biodiesel yield also decreases [8][9][10][11][12][13][14][15][16]. The objective of this study was the assay of specific conditions in salinity and nitrogen deficiency and air bubbling that could stimulate the triglycerides production, while the negative effect over the biomass is mitigated.…”

Microalgae of Odisha Coast as a Potential Source for Biodiesel Production

“…The content of lipid, carbohydrate and proteins varies from species to species. Most common algae like Chlorella, Crypthecodinium, Cylindrotheca, Dunaliella, Isochrysis, Nannochloris, Nannochloropsis, Neochloris, Nitzschia, Phaeodactylum, Porphyridium, Schizochytrium, Tetraselmis, Botryococcus braunii and Scenedesmus have oil levels between 20 and 50% but higher productivities can be reached [1,[16][17][18][19][20]. Under adverse growth conditions such as nitrogen limitation, low temperature, high light intensity, high salt concentration and high iron concentration the lipid content in some of microalgae increased [21,19].…”