Nitrogen Starvation Induced Oxidative Stress in an Oil-Producing Green Alga Chlorella sorokiniana C3

Abstract

Microalgal lipid is one of the most promising feedstocks for biodiesel production. Chlorella appears to be a particularly good option, and nitrogen (N) starvation is an efficient environmental pressure used to increase lipid accumulation in Chlorella cells. The effects of N starvation of an oil-producing wild microalga, Chlorella sorokiniana C3, on lipid accumulation were investigated using thin layer chromatography (TLC), confocal laser scanning microscopy (CLSM) and flow cytometry (FCM). The results showed that N starvation resulted in lipid accumulation in C. sorokiniana C3 cells, oil droplet (OD) formation and significant lipid accumulation in cells were detected after 2 d and 8 d of N starvation, respectively. During OD formation, reduced photosynthetic rate, respiration rate and photochemistry efficiency accompanied by increased damage to PSII were observed, demonstrated by chlorophyll (Chl) fluorescence, 77K fluorescence and oxygen evolution tests. In the mean time the rate of cyclic electron transportation increased correspondingly to produce more ATP for triacylglycerols (TAGs) synthesis. And 0.5 d was found to be the turning point for the early stress response and acclimation of cells to N starvation. Increased level of membrane peroxidation was also observed during OD formation, and superoxide dismutase (SOD), peroxide dismutase (POD) and catalase (CAT) enzyme activity assays suggested impaired reactive oxygen species (ROS) scavenging ability. Significant neutral lipid accumulation was also observed by artificial oxidative stress induced by H2O2 treatment. These results suggested coupled neutral lipid accumulation and oxidative stress during N starvation in C. sorokiniana C3.

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

“…This study shows the synergistic effect of two different stresses, i.e., the addition of hydrogen peroxide and nutrient starvation. This synergistic effect was also apparent in a study by Zhang et al (2013) on Chlorella sorokiniana C3. In fact, they found that hydrogen peroxide addition is able to induce more lipid accumulation than nutrient starvation.…”

The acclimation of Chlorella to high-level nitrite for potential application in biological NOx removal from industrial flue gases

“…The N-sufficient (17.65 mmol L −1 nitrate) medium used for the control group was full-strength BG11 medium (Stanier et al, 1971), whereas the N-free medium was BG11 without NaNO 3 . Cells cultured with fullstrength BG11 were harvested at mid-logarithmic growth phase (OD 700 value approximately 0.8) by centrifuging the culture at 3000g for 3 min, at 20 • C; the pellet was then washed with N-free BG11 medium and re-suspended to OD 700 0.5 in either regular BG11 or N-free medium with sodium nitrite added as the nitrogen source at various concentrations (Zhang et al, 2013). For the nitrite treatment, the nitrite concentrations were 17.65, 35.3, 88.25, and 176.5 mmol L −1 (1 × , 2 × , 5 × , and 10 × NaNO 2 ) (Zhang et al, 2014a).…”

“…All Chlorella strains were cultured as described above in either BG11 or 10 × NaNO 2 (176.5 mmol L −1 ) medium for 10 days (the starting optical density OD 700 was 0.05) (Zhang et al, 2013). OD 700 values were measured with a spectrophotometer every 24 h. The OD data were used to generate the cell growth curves.…”

“…Photosynthetic oxygen evolution and dark respiration rates. Rates of steady-state photosynthetic oxygen evolution and respiration were measured using a Clark-type oxygen electrode (Oxylab 2, Hansatech, UK) at 25 • C, as described before (Zhang et al, 2013). Cell suspensions (2 ml, OD 700 = 1.0) were illuminated at a quantum flux density of 300 mol m −2 s −1 .…”

An informatics-based analysis of developments to date and prospects for the application of microalgae in the biological sequestration of industrial flue gas

“…As one of the oldest lower photosynthetic organisms, some microalgae can directly use sunlight, CO 2 , nitrogen (N), phosphorus (P), and other simple nutrient substances to grow rapidly and to synthesize fat (primarily triglycerides) which could provide new oil resource for biodiesel production Gao et al 2013;Zhang et al 2013). Microalgal biomass contains approximately 50 % carbon and 7-12 % nitrogen by dry weight (Miron et al 2003).…”