Lipid Accumulation Stage Research Articles

Linking lipid accumulation and photosynthetic efficiency in Nannochloropsis sp. under nutrient limitation and replenishment

Oleaginous microalgae can accumulate large amounts of storage lipids that have many potential applications such as in the production of biodiesel and health products. All of the energy for the synthesis of lipids in microalgae is derived from photosynthesis. To date, however, the quantitative relationship between photosynthesis and lipid accumulation rate in microalgae is still unclear. In this study, Nannochloropsis sp. was selected to explore this relationship by investigating changes in lipid accumulation, photosynthetic efficiency, and the electron transport chain under nutrients limitation and replenishment. The results of the study demonstrated that lipids were the main form of storage of carbon and energy for this microalga. The alternative electron transport chain played an important role in photo-protection and lipid accumulation. The photosynthetic efficiency of this microalga showed a strong correlation with lipid accumulation rate (R2 = 0.959), with higher photosynthetic efficiency translating to higher lipid accumulation rates during the lipid accumulation stage of the growth cycle. The results of the present study indicated that nutrient depletion might not be the best signal to understand when microalgae begin to accumulate oil, as it appears that photosynthetic efficiency also has a large role in the rate of oil accumulation. Additionally, the study shows that excessive light might not be needed in later stages of growth for lipid accumulation, which in turn would alleviate the damage to microalgae caused by strong light making large-scale cultivation more cost-effective.

Growth kinetics, fatty acid composition and metabolic activity changes of Crypthecodinium cohnii under different nitrogen source and concentration

The effect of varying concentrations of the nitrogen source on the growth kinetics, lipid accumulation, lipid and DHA productivity, and fatty acid composition of C. cohnii was elucidated. Growth of C. cohnii was in three distinct growth stages: cell growth, lipid accumulation and a final lipid turnover stage. Most of lipids were accumulated in lipid accumulation stage (48–120 h) though, slow growth rate was observed during this stage. NaNO3 supported significantly higher lipid content (26.9% of DCW), DHA content (0.99 g/L) and DHA yield (44.2 mg/g glucose) which were 2.5 to 3.3-folds higher than other N-sources. The maximum level of C16–C18 content (% TFA) was calculated as 43, 54 and 43% in lipid accumulation stage under low nitrogen (LN, 0.2 g/L), medium nitrogen (MN, 0.8 g/L) and high nitrogen (HN, 1.6 g/L) treatments, respectively. Cultures with LN, by down-regulating cell metabolism, trigger onset of lipogenic enzymes. Conversely, NAD+/NADP+-dependent isocitrate dehydrogenase (NAD+/NADP+-ICDH) were less active in LN than HN treatments which resulted in retardation of Kreb’s Cycle and thereby divert citrate into cytoplasm as substrate for ATP-citrate lyase (ACL). Thereby, ACL and fatty acid synthase (FAS) were most active in lipid accumulation stage at LN treatments. Glucose-6-phosphate dehydrogenase (G6PDH) was more active than malic enzyme (ME) in lipid accumulation stage and showed higher activities in NaNO3 than other N-sources. This represents that G6PDH contributes more NADPH than ME in C. cohnii. However, G6PDH and ME together seems to play a dual role in offering NADPH for lipid biosynthesis. This concept of ME together with G6PD in offering NADPH for lipogenesis might be novel in this alga and needed to be explored.

Improvement of docosahexaenoic acid fermentation from Schizochytrium sp. AB-610 by staged pH control based on cell morphological changes.

Schizochytrium sp. AB-610 accumulates relatively higher amount of DHA-rich lipid in the cells, and it was found that DHA yield was closely related to the cell morphology and pH value during fermentation period. DHA production from Schizochytrium sp. AB-610 in fed-batch fermentation was investigated and four growth stages were clarified as lag stage, balanced growth stage, lipid accumulation stage, and lipid turnover stage, based on the morphologic observation and key parameters changes. Then a simple strategy of two-stage pH control was developed, in which pH 7.0 was kept until 12 h after the end of balanced growth stage, and then shifted to 5.0 for the rest period in fermentation. A maximal DHA production of 11.44g/L was achieved. This approach has advantage of easy scaling up for industrial DHA fermentation from Schizochytrium sp. cells.

Lipid quantification by Raman microspectroscopy as a potential biomarker in prostate cancer

Metastatic castration-resistant prostate cancer (mCRPC) remains incurable and is one of the leading causes of cancer-related death among American men. Therefore, detection of prostate cancer (PCa) at early stages may reduce PCa-related mortality in men. We show that lipid quantification by vibrational Raman Microspectroscopy and Biomolecular Component Analysis may serve as a potential biomarker in PCa. Transcript levels of lipogenic genes including sterol regulatory element-binding protein-1 (SREBP-1) and its downstream effector fatty acid synthase (FASN), and rate-limiting enzyme acetyl CoA carboxylase (ACACA) were upregulated corresponding to both Gleason score and pathologic T stage in the PRAD TCGA cohort. Increased lipid accumulation in late-stage transgenic adenocarcinoma of mouse prostate (TRAMP) tumors compared to early-stage TRAMP and normal prostate tissues were observed. FASN along with other lipogenesis enzymes, and SREBP-1 proteins were upregulated in TRAMP tumors compared to wild-type prostatic tissues. Genetic alterations of key lipogenic genes predicted the overall patient survival using TCGA PRAD cohort. Correlation between lipid accumulation and tumor stage provides quantitative marker for PCa diagnosis. Thus, Raman spectroscopy-based lipid quantification could be a sensitive and reliable tool for PCa diagnosis and staging.

Evaluating feeding strategies for microbial oil production from glycerol by Rhodotorula glutinis.

Oil production, from biodiesel by-product glycerol, through microbial fermentation provides a promising option as part of an integrated biorefinery process. However, bioprocessing improvements are required to make the process more efficient. In the present work, different glycerol feeding strategies were evaluated under fed-batch cultivation of the oleaginous yeast Rhodotorula glutinis. Results showed that the concept of targeting first a cell proliferation stage and then a lipid accumulation stage had beneficial effects on both biomass and oil yields. Continual feeding and pulsed feedings, delivering the same total amount of nutrients, resulted in similar values of cellular biomass (∼25 g/L) and oil content (∼40%). In contrast, continual supply of nutrients at higher rates ( >0.8 g/L/h) led to an increase in both cell densities (30 g/L) and oil content (53%), attaining a high oil yield of 16.28 g/L. This suggests that a continual cultivation with two different rates for each stage constitutes an efficient approach to enhance microbial oil production.

Salinity stress increases lipid, secondary metabolites and enzyme activity in Amphora subtropica and Dunaliella sp. for biodiesel production

Amphora subtropica and Dunaliella sp. isolated from Tunisian biotopes were retained for their high lipid contents. Respective optimized parameters for rapid growth were: pH 9 and 10, light period 21 and 24h and temperature 31 and 34°C, respectively. After optimization, Amphora subtropica growth rate increased from 0.2 to 0.5day−1 and Dunaliella sp. growth rate increased from 0.38 to 0.7day−1. Amphora subtropica biomass production, productivity and lipid content increased from 0.3 to 0.7gL−1(dw), 69–100mgL−1d−1(dw) and 150–190gkg−1(dw), respectively, and Dunaliella sp. from 0.5 to 1.4gL−1(dw), 124–200mgL−1d−1 (dw) and 190–280gkg−1(dw), respectively. Often to overcome trade-off between microalgae rapid growth and high lipid content which are often conflicting and very difficult to obtain at the same time, separation in a growth stage and a lipid accumulation stage is obvious. Salinity stress in a single stage of culture was studied. Compared to the optimal concentration of growth, excess or deficiency of NaCl engendered the same cellular responses by implication of oxidative stress systems and reactivation of defense and storage systems. Indeed, increasing salinity from 1M to 2M for Amphora subtropica or decreasing salinity from 3M to 2M for Dunaliella sp. have both increased lipids content from (220 and 280) to (350 and 430)gkg−1, carotenoids from (1.8 and 2.4) to (2.3 and 3.7)pgcell−1, TBARS amount from (10.4 and 5.3) to (12.1 and 10.7)nmolmg−1 proteins and SOD activity from of (46.6 and 61.8) to (71.6 and 79.4)Umg−1 proteins, respectively. With further improved fatty acids profile, the microalgae strains could be potent candidates for biofuel production.

Effect of malate on docosahexaenoic acid production from Schizochytrium sp. B4D1

Background: Malate involves in the citrate/malate and transhydrogenase cycles to provide precursors for docosahexaenoic acid (DHA) synthesis. The optimal strategy was investigated for increasing DHA production in Schizochytrium species during fermentation. Results: DHA production increased by 47% and reached 5.51 g/L when 4 g malate/L was added during the rapid lipid accumulation stage in shake-flasks culture. Inducing effects of malate was further investigated through the analysis of three kinetic parameters, including specific cell growth rate (μ), specific glucose consumption rate (q Glu ) and DHA formation rate (q DHA ). DHA concentration was enhanced through a novel fed-batch strategy to a maximum value of 30.7 g/L, giving a yield of 0.103 g DHA/g glucose and a productivity of 284 mg L - 1 h - 1 . Conclusion: A novel malate feeding strategy was developed that enhanced DHA yield and productivity of Schizochytrium species which may offer a desirable method for industrial applications. Normal 0 21 false false false EN-US ZH-CN X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabla normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.5pt; mso-bidi-font-size:11.0pt; font-family:Calibri,sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-font-kerning:1.0pt; mso-ansi-language:EN-US; mso-fareast-language:ZH-CN;}

Transcriptome and gene expression analysis of DHA producer Aurantiochytrium under low temperature conditions.

Aurantiochytrium is a promising docosahexaenoic acid (DHA) production candidate due to its fast growth rate and high proportions of lipid and DHA content. In this study, high-throughput RNA sequencing technology was employed to explore the acclimatization of this DHA producer under cold stress at the transcriptional level. The overall de novo assembly of the cDNA sequence data generated 29,783 unigenes, with an average length of 1,200 bp. In total, 13,245 unigenes were annotated in at least one database. A comparative genomic analysis between normal conditions and cold stress revealed that 2,013 genes were differentially expressed during the growth stage, while 2,071 genes were differentially expressed during the lipid accumulation stage. Further functional categorization and analyses showed some differentially expressed genes were involved in processes crucial to cold acclimation, such as signal transduction, cellular component biogenesis, and carbohydrate and lipid metabolism. A brief survey of the transcripts obtained in response to cold stress underlines the survival strategy of Aurantiochytrium; of these transcripts, many directly or indirectly influence the lipid composition. This is the first study to perform a transcriptomic analysis of the Aurantiochytrium under low temperature conditions. Our results will help to enhance DHA production by Aurantiochytrium in the future.

Comparison on the carbohydrate metabolic enzyme activities and their gene expression patterns in canola differing seed oil content

Carbohydrates are an important regulator of canola seed oil content. However, understanding the physiological regulation by carbohydrates governing seed oil accumulation is fragmented. In the present study, activities of sucrose and starch catalytic enzymes, including neutral and alkaline invertase, sucrose synthase (SUS), and starch phosphorylase, and biosynthetic enzymes, including sucrose phosphate synthase and ADP-glucose pyrophosphorylase, were compared in developing silique and seed of high oil content and low oil content lines (HOCL and LOCL, respectively). The results showed that the HOCL had significantly higher total soluble sugar concentration in the developing silique wall and seed during the seed lipid accumulation stage. Strikingly, all the enzymes showed very strong activities at 20 days after anthesis in the silique wall of the HOCL, which was in agreement with the higher amounts of corresponding gene expression. The result indicated that the homeostasis of the high efficiency of cleavage and biosynthetic of carbohydrates in the HOCL was beneficial for the rapid volume expansion of silique and transportation of carbohydrates, i.e., sucrose and starch, to the seed for utilization. At seed deposition stage, all the enzymes exhibited significantly higher activities in the HOCL than in the LOCL, which was helpful for increased production of carbohydrates. The results of gene expression at seed oil deposition stages revealed that one of the SUS genes, SUS3, showed significantly higher transcript amount in the HOCL than in the LOCL at all stages while most of other genes showed no significant differences between two lines at developing stages. Therefore, SUS3 might be played vital roles in the sucrose cleavage.

High-cell-density cultivation of an engineered Rhodococcus opacus strain for lipid production via co-fermentation of glucose and xylose

An engineered strain MITXM-61 of Rhodococcus opacus PD630 capable of utilizing xylose was used to produce biofuel precursor-triacylglycerols (TAG) from mixed glucose–xylose substrates. Optimal nitrogen source and carbon source concentrations were investigated for cell growth and microbial lipid production by MITXM-61 in flask cultures. In a two-stage batch culture, the maximum lipid yield (0.152gTAGperg consumed carbon source) was achieved by utilizing a mixture of glucose and xylose. The fed-batch culture featured intermittent feeding of refined xylose solution during the lipid accumulation stage provided 45gL−1 of cell dry weight, 54% (gTAGperg cell dry weight) of lipid content, 0.179gg−1 (gTAGperg consumed carbon source) of lipid yield, and a 6.9gL−1day−1 of lipid productivity. Fatty acids extracted from microbial lipids produced by MITXM-61 were predominately palmitic and oleic acids, which are the major components in TAG-derived biofuels.

Hormones, Polyamines, and Cell Wall Metabolism during Oil Palm Fruit Mesocarp Development and Ripening

Oil palm is one of the most productive oil-producing crops and can store up to 90% oil in its fruit mesocarp. Oil palm fruit is a sessile drupe consisting of a fleshy mesocarp from which palm oil is extracted. Biochemical changes in the mesocarp cell walls, polyamines, and hormones at different ripening stages of oil palm fruits were studied, and the relationship between the structural and the biochemical metabolism of oil palm fruits during ripening is discussed. Time-course analysis of the changes in expression of polyamines, hormones, and cell-wall-related genes and metabolites provided insights into the complex processes and interactions involved in fruit development. Overall, a strong reduction in auxin-responsive gene expression was observed from 18 to 22 weeks after pollination. High polyamine concentrations coincided with fruit enlargement during lipid accumulation and latter stages of maturation. The trend of abscisic acid (ABA) concentration was concordant with GA₄ but opposite to the GA₃ profile such that as ABA levels increase the resulting elevated ABA/GA₃ ratio clearly coincides with maturation. Polygalacturonase, expansin, and actin gene expressions were also observed to increase during fruit maturation. The identification of the master regulators of these coordinated processes may allow screening for oil palm variants with altered ripening profiles.

Compositional shift in lipid fractions during lipid accumulation and turnover in Schizochytrium sp.

Single cell oils (SCOs), a complex lipid system, contains neutral lipids (NLs), polar lipids (PLs) and unsaponifiable matters (UMs). To investigate the dynamic changes and the metabolic competition mechanism of different components of SCOs, changes in lipid composition of Schizochytrium sp. were monitored in lipid accumulation and turnover stages. Lipid content could reach 69.98% in biomass during the lipid accumulation stage, while, after the exhaustion of glucose, the content decreased to 45.51% and 20.6g/L non-oil biomass was synthesis. Polyunsaturated fatty acids (PUFAs) were easier to bind with PLs. NLs were preferentially converted to PLs during lipid turnover stage, accompanied by the degradation of saturated fatty acids and the increase of UMs. Meanwhile, a positive correlation between the synthesis of PUFAs and unsaponifiable matters exited in Schizochytrium sp., and increasing the content of UMs from 45 to 100mg/L could increase the PUFA percentage from 64% to 74% effectively.

Comparative Proteomics Profile of Lipid-Cumulating Oleaginous Yeast: An iTRAQ-Coupled 2-D LC-MS/MS Analysis

Accumulation of intracellular lipid in oleaginous yeast cells has been studied for providing an alternative supply for energy, biofuel. Numerous studies have been conducted on increasing lipid content in oleaginous yeasts. However, few explore the mechanism of the high lipid accumulation ability of oleaginous yeast strains at the proteomics level. In this study, a time-course comparative proteomics analysis was introduced to compare the non-oleaginous yeast Saccharomyces cerevisiae, with two oleaginous yeast strains, Cryptococcus albidus and Rhodosporidium toruloides at different lipid accumulation stages. Two dimensional LC-MS/MS approach has been applied for protein profiling together with isobaric tag for relative and absolute quantitation (iTRAQ) labelling method. 132 proteins were identified when three yeast strains were all at early lipid accumulation stage; 122 and 116 proteins were found respectively within cells of three strains collected at middle and late lipid accumulation stages. Significantly up-regulation or down-regulation of proteins were experienced among comparison. Essential proteins correlated to lipid synthesis and regulation were detected. Our approach provides valuable indication and better understanding for lipid accumulation mechanism from proteomics level and would further contribute to genetic engineering of oleaginous yeasts.

Enhanced docosahexaenoic acid production by reinforcing acetyl-CoA and NADPH supply in Schizochytrium sp. HX-308

Docosahexaenoic acid (DHA) production in Schizochytrium sp. HX-308 was evaluated by detecting enzymatic activities of ATP:citrate lyase (EC 4.1.3.8), malic enzyme (EC 1.1.1.40) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) at different fermentation stages. According to the analysis, a regulation strategy was proposed which reinforced acetyl-CoA and NADPH supply at a specific fermentation stage. DHA content of total fatty acids was increased from 35 to 60% by the addition of 4 g/L malic acid at the rapid lipid accumulation stage. Total lipid content also showed an apparent increase of 35% and reached 19 g/L when 40 mL ethanol/L was added at the late lipid accumulation stage.