Lipid Profile Remodeling in Response to Nitrogen Deprivation in the Microalgae Chlorella sp. (Trebouxiophyceae) and Nannochloropsis sp. (Eustigmatophyceae)

Abstract

Many species of microalgae produce greatly enhanced amounts of triacylglycerides (TAGs), the key product for biodiesel production, in response to specific environmental stresses. Improvement of TAG production by microalgae through optimization of growth regimes is of great interest. This relies on understanding microalgal lipid metabolism in relation to stress response in particular the deprivation of nutrients that can induce enhanced TAG synthesis. In this study, a detailed investigation of changes in lipid composition in Chlorella sp. and Nannochloropsis sp. in response to nitrogen deprivation (N-deprivation) was performed to provide novel mechanistic insights into the lipidome during stress. As expected, an increase in TAGs and an overall decrease in polar lipids were observed. However, while most membrane lipid classes (phosphoglycerolipids and glycolipids) were found to decrease, the non-nitrogen containing phosphatidylglycerol levels increased considerably in both algae from initially low levels. Of particular significance, it was observed that the acyl composition of TAGs in Nannochloropsis sp. remain relatively constant, whereas Chlorella sp. showed greater variability following N-deprivation. In both algae the overall fatty acid profiles of the polar lipid classes were largely unaffected by N-deprivation, suggesting a specific FA profile for each compartment is maintained to enable continued function despite considerable reductions in the amount of these lipids. The changes observed in the overall fatty acid profile were due primarily to the decrease in proportion of polar lipids to TAGs. This study provides the most detailed lipidomic information on two different microalgae with utility in biodiesel production and nutraceutical industries and proposes the mechanisms for this rearrangement. This research also highlights the usefulness of the latest MS-based approaches for microalgae lipid research.

A biorefinery for Nannochloropsis: Induction, harvesting, and extraction of EPA-rich oil and high-value protein

“…Nevertheless, the decrease in the other lipid classes is not equivalent to the increase in the content of the neutral lipids. This observation implies that, aside from the rearrangement of some polar lipids to form neutral lipids, de novo fatty acid synthesis is also induced (Martin et al, 2014;Simionato et al, 2013).…”

“…Martin et al (2014) showed a 52% increase in the total lipid of nitrogen-depleted Nannochloropsis sp. Furthermore, Bondioli et al (2012) observed a 75% increase in the lipid content for the nitrogen depleted Nannochloropsis sp.…”

“…Most of these neutral lipids are triacylglycerides (TAGs); however, there are notable decreases in the other lipid classes (Martin et al, 2014;Simionato et al, 2013). Nevertheless, the decrease in the other lipid classes is not equivalent to the increase in the content of the neutral lipids.…”

Nitrate Reductase Knockout Uncouples Nitrate Transport from Nitrate Assimilation and Drives Repartitioning of Carbon Flux in a Model Pennate Diatom

“…Increases in TAG inversely track with the decline in C20:5 FA concentrations in both cell types (Supplemental Figures 7C and 7D). In P. tricornutum and other microalgae, the decrease in C20:5 FA during N-stress is believed to reflect the efforts by alga to pursue a second source for TAG by recycling C20:5 and C16 FA moieties from chloroplast thylakoid membrane glycerolipids (Abida et al, 2015;Li et al, 2012;Martin et al, 2014;Simionato et al, 2013). Specific galactoglycerolipid lipases, known in plants as patatin lipases (reviewed in Scherer et al, 2010), have been functionally characterized in C. reinhardtii and Nannochloropsis oceanica Li et al, 2014) as thylakoid glycerolipid recyclers.…”

Light Remodels Lipid Biosynthesis in Nannochloropsis gaditana by Modulating Carbon Partitioning between Organelles

“…Lipid accumulation in several algal species is triggered by nitrogen (N) depletion, and these conditions have been heavily investigated to understand lipid metabolism regulation (Miller et al, 2010;Simionato et al, 2013;Li et al, 2014;Lu et al, 2014;Martin et al, 2014;Abida et al, 2015;Jia et al, 2015). Nitrogen deprivation also leads to accumulation of storage sugars like starch or chrysolaminarin, depending on the organism (Jia et al, 2015), and the impairment of the storage sugar metabolism was observed to further increase TAGs (Blaby et al, 2013).…”