Responses of Nannochloropsis oceanica IMET1 to Long-Term Nitrogen Starvation and Recovery      

Abstract

The Nannochloropsis genus contains oleaginous microalgae that have served as model systems for developing renewable biodiesel. Recent genomic and transcriptomic studies on Nannochloropsis species have provided insights into the regulation of lipid production in response to nitrogen stress. Previous studies have focused on the responses of Nannochloropsis species to short-term nitrogen stress, but the effect of long-term nitrogen deprivation remains largely unknown. In this study, physiological and proteomic approaches were combined to understand the mechanisms by which Nannochloropsis oceanica IMET1 is able to endure long-term nitrate deprivation and its ability to recover homeostasis when nitrogen is amended. Changes of the proteome during chronic nitrogen starvation espoused the physiological changes observed, and there was a general trend toward recycling nitrogen and storage of lipids. This was evidenced by a global down-regulation of protein expression, a retained expression of proteins involved in glycolysis and the synthesis of fatty acids, as well as an up-regulation of enzymes used in nitrogen scavenging and protein turnover. Also, lipid accumulation and autophagy of plastids may play a key role in maintaining cell vitality. Following the addition of nitrogen, there were proteomic changes and metabolic changes observed within 24 h, which resulted in a return of the culture to steady state within 4 d. These results demonstrate the ability of N. oceanica IMET1 to recover from long periods of nitrate deprivation without apparent detriment to the culture and provide proteomic markers for genetic modification.

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

“…PSII maximum efficiency [expressed as F v /F m = (F m -F 0 )/F m ] was monitored through in vivo chlorophyll fluorescence determination with the DUAL-PAM-100 fluorimeter (Heinz-Walz). F v /F m under LL and ML conditions was consistent with the one reported for various Nannochloropsis species in other works (Kotabová et al, 2011;Simionato et al, 2011;Dong et al, 2013). PSII functional antenna size (ASII) was determined using a JTS10 spectrophotometer (Bio-Logic) at a concentration of 200 * 10 6 cells/mL, with 80 mM DCMU incubation for 10 min.…”

Choreography of Transcriptomes and Lipidomes ofNannochloropsisReveals the Mechanisms of Oil Synthesis in Microalgae

“…Previous studies of the unicellular green alga C. reinhardtii suggested that conversion of storage polysaccharides (e.g., starch) into the precursors for lipid biosynthesis contributed to TAG accumulation under N-conditions (Li et al, 2010b(Li et al, , 2011Work et al, 2010). Microscope observations indicated Nannochloropsis cells lack pyrenoid starch (Vieler et al, 2012;Dong et al, 2013), consistent with the absence of genes responsible for starch biosynthesis in the IMET1 genome. Laminarin and chrysolaminarin, which are glucans with various ratios of b-(1,3) to b-(1,6)-linked Glc, with predominantly b-(1,3)-linkages, have been suggested to be the major storage carbohydrate in heterokonts (Beattie et al, 1961).…”

Ultrastructure and Composition of the Nannochloropsis gaditana Cell Wall

“…No trace of sucrose or fructose could be found in the resulting preparations when digested and analyzed by IC. The Takeda method also includes an ␣-amylase digestion to remove starch, but this step was deemed unnecessary because (i) Nannochloropsis species are not believed to produce starch, as is also the case for other stramenopiles (94), (ii) no starch grains are evident by QFDE-EM of intact cells, and (iii) genomic evidence of starch biosynthetic enzymes (i.e., starch synthase and isoamylase) is lacking (5,9,40,68,93,(95)(96)(97). Furthermore, the low abundance of 1,3-linked glucose detected, combined with the absence of detectable mannitol, suggested minimal contamination with laminarin, a storage product common in related brown algae (98).…”