Nitrogen and phosphorus stress as a tool to induce lipid production in microalgae

Microalgae, capable of accumulating large amounts of lipids, are of great value for biodiesel production. The high cost of such production stimulates the search for cultivation conditions that ensure their highest productivity. Reducing the content of nitrogen and phosphorus in the culture medium is widely used to change the content and productivity of lipids in microalgae. Achieving the right balance between maximum growth and maximum lipid content and productivity is the primary goal of many experimental works to ensure cost-effective biodiesel production from microalgae. The content of nitrogen and phosphorus in nutrient media for algal cultivation after converted to nitrogen (-N) and phosphorus (-P) lies in an extensive range: from 0.007 g L- 1 to 0.417 g L- 1 and from 0.0003 g L- 1 to 0.227 g L- 1 and N:P ratio from 0.12:1 to 823.33:1. When studying nutritional stress in microalgae, no single approach is used to determine the experimental concentrations of nitrogen and phosphorus. This precludes the possibility of correct interpretation of the data and may lead to erroneous conclusions. This work results from the systematisation of information on using nitrogen and phosphorus restriction to increase the lipid productivity of microalgae of different taxonomic and ecological groups to identify future research directions. The results of 301 experiments were included in the analysis using the principal components method. The investigation considered various divisions and classes: Cyanobacteria, Rhodophyta, Dinophyta, Haptophyta, Cryptophyta, Heterokontophyta/Ochrophyta (Bacillariophyceae, Eustigmatophyceae, Xanthophyceae), Chlorophyta, and also the ratio N:P, the time of the experiment, the light intensity during cultivation. Based on the concentrations of nitrogen and phosphorus existing in various nutrient media, a general scheme for designating the supply of nutrient media for nitrogen (as NO3- or NH4+, N g L- 1) and phosphorus (as РO4-, P g L- 1) has been proposed: replete -N (˃0.4 g L- 1), moderate -N (0.4-0.2), moderate N-limitation (0.19-0.1), strong N-limitation (˂0.1), without nitrogen (0), replete -Р (˃0.2), moderate -P (0.2-0.02), moderate P-limitation (0.019-0.01), strong P-limitation (˂0.01), without phosphorus (0).

Development of Microalgae Biodiesel: Current Status and Perspectives

Microalgae are regarded as a promising source of biodiesel. In contrast with conventional crops currently used to produce commercial biodiesel, microalgae can be cultivated on non-arable land, besides having a higher growth rate and productivity. However, microalgal biodiesel is not yet regarded as economically competitive, compared to fossil fuels and crop-based biodiesel; therefore, it is not commercially produced. This review provides an overall perspective on technologies with the potential to increase efficiency and reduce the general costs of biodiesel production from microalgae. Opportunities and challenges for large-scale production are discussed. We present the current scenario of Brazilian research in the field and show a successful case in the research and development of microalgal biodiesel in open ponds by Petrobras. This publicly held Brazilian corporation has been investing in research in this sector for over a decade.

Nutritional conditions of the novel freshwater Coccomyxa AP01 for versatile fatty acids composition

AIMS

This study was to analyse the biomass production and fatty acids (FAs) profiles in a newly isolated chlorophyte, namely Coccomyxa AP01, under nutritionally balanced (NB) conditions (comparing nitrate and urea as nitrogen sources) and nitrogen or phosphate deprivation.

METHODS AND RESULTS

Lipid yields was about 30%-40% of dried biomasses in all examined nutritional conditions. Under NB conditions, lipids were principally constituted by monounsaturated FAs, mainly represented by oleic acid, and saturated and polyunsaturated FAs at similar concentrations. Nutrients deprivation induced remarkable changes in FAs profiles, with the highest amounts of saturated (42%-46%), followed by similar amounts of monounsaturated and polyunsaturated, and the emergence of rare long-chain FAs. Under phosphate deprivation, biomass yield was similar to NB conditions, with the highest yield of saturated (mainly palmitic acid) and of polyunsaturated FAs (33%) (mainly linoleic and linolenic acids).

CONCLUSIONS

Balanced or deprived nutritional conditions in Coccomyxa AP01 induced a selective production and composition of FAs. The phosphate-deprivation condition concomitantly provided high biomass yield and the production of high value saturated and polyunsaturated FAs with industrial interest.

SIGNIFICANCE AND IMPACT OF THE STUDY

Coccomyxa AP01 could be considered a promising source of different FAs, including also docosapentaenoic acid, for several commercial purposes spanning from biodiesel production, pharmaceutical and cosmetic applications to innovative aquaculture fish feeds.

Co-Cultivation of Leptolyngbya tenuis (Cyanobacteria) and Chlorella ellipsoidea (Green alga) for Biodiesel Production, Carbon Sequestration, and Cadmium Accumulation

The co-cultivation approach using cyanobacteria-Leptolyngbya tenuis and green alga-Chlorella ellipsoidea demonstrated in the present study showed additive and synergistic effects on biomass yield, biomass productivity, lipid yield, lipid productivity, CO₂ fixation, and cadmium bioremediation efficiency. The results of co-culture in batch mode revealed about 2-3 times increase in biomass and two times increase in total lipid, when compared to the pure culture batches. The results revealed that co-cultures exhibited significantly high CO₂ fixation rate of 2.63  ±  0.09 g/L/d, which is 1.5-2 times better than monocultures (P < 0.05). To explore the bioaccumulation of cadmium by co-cultures and pure cultures, different concentrations of cadmium nitrate was used in flask trials. Cadmium accumulation was observed in the order: co-culture (74%, 0.37 mg/L) > Chlorella (58%, 0.29 mg/L) > Leptolyngbya (50%, 0.25 mg/L) (P < 0.05). In addition, fatty acid composition, CHNS analysis, biodiesel characterization, and biochemical compositions were also determined using co-culture method. The maximum biomass yield, productivity, lipid content, and CO₂ fixation rate in cadmium induced co-culture were 3.95  ±  0.13 g/L, 258.88  ±  15.75 mg/L/d, 41.43  ±  0.71%, and 3.21  ±  0.20 g/L/d, respectively which is 1.2, 1.3, 2.3, and 1.2 times higher than the control (P < 0.05). Cadmium induced changes in growth and lipid yield using co-culture suggests cost-effective and eco-friendly production of biodiesel and carbon mitigation.

Influence of Nitrogen and Phosphorus on Microalgal Growth, Biomass, Lipid, and Fatty Acid Production: An Overview

Microalgae can be used as a source of alternative food, animal feed, biofuel, fertilizer, cosmetics, nutraceuticals and for pharmaceutical purposes. The extraction of organic constituents from microalgae cultivated in the different nutrient compositions is influenced by microalgal growth rates, biomass yield and nutritional content in terms of lipid and fatty acid production. In this context, nutrient composition plays an important role in microalgae cultivation, and depletion and excessive sources of this nutrient might affect the quality of biomass. Investigation on the role of nitrogen and phosphorus, which are crucial for the growth of algae, has been addressed. However, there are challenges for enhancing nutrient utilization efficiently for large scale microalgae cultivation. Hence, this study aims to highlight the level of nitrogen and phosphorus required for microalgae cultivation and focuses on the benefits of nitrogen and phosphorus for increasing biomass productivity of microalgae for improved lipid and fatty acid quantities. Furthermore, the suitable extraction methods that can be used to utilize lipid and fatty acids from microalgae for biofuel have also been reviewed.

The effect on single and combined stresses for biomass and lipid production from Nannochloris atomus using two phase culture system

The optimal conditions for high biomass and lipid production from Nannochloris atomus were evaluated. The parameters used in this study were light emitting diode (LED) wavelength mixing ratio, the photoperiod, salinity tolerance, and single and combined stresses. Biomass production was monitored in the first phase using red LED (625 nm), followed by lipid production by green LED (520 nm) in the second phase. The optimal conditions were obtained using a single red LED with light:dark durations of 20:4 h and two days of exposure in combined stresses of 1.06 M NaCl and green LED. Under these conditions, 68.6 % (w/w) lipid content were obtained. Compared to the non-stress control, the lipid content was increased by 31.9 %. Linolenic acid (C18:3) the omega-3 fatty acid was produced up to 52.4 % in 1.06 M NaCl as a single stress.

Incorporation of Magnetic Nanoparticles into Protoplasts of Microalgae Haematococcus pluvialis: A Tool for Biotechnological Applications

Intensive research on the use of magnetic nanoparticles for biotechnological applications of microalgae biomass guided the development of proper treatment to successfully incorporate them into these single-cell microorganisms. Protoplasts, as cells lacking a cell wall, are extensively used in plant/microalgae genetic manipulation as well as various biotechnological applications. In this work, a detailed study on the formation of protoplasts from Haematococcus pluvialis with the use of enzymatic and mechanical procedures was performed. The optimization of several parameters affecting the formation of protoplasmic cells and cell recovery was investigated. In the enzymatic treatment, a solution of cellulase was studied at different time points of incubation, whereas in the mechanical treatment, glass beads vortexing was used. Mechanical treatment gave better results in comparison to the enzymatic one. Concerning the cell recovery, after the protoplast formation, it was found to be similar in both methods used; cell viability was not investigated. To enhance the protoplast cell wall reconstruction, different “recovery media” with an organic source of carbon or nitrogen were used. Cell morphology during all treatments was evaluated by electron microscopy. The optimal conditions found for protoplast formation and cell reconstruction were successfully used to produce Haematococcus pluvialis cells with magnetic properties.

A Study on the Effect of Macro- and Micro- Nutrients on Nannochloropsis oceanica Growth, Fatty Acid Composition and Magnetic Harvesting Efficiency

The effect of iron, manganese, phosphorus and nitrogen on growth and lipid synthesis of the microalgae Nannochloropsis oceanica CCMP1779, as well as their impact on the magnetic harvesting efficiency, are examined under their depriving cell culture conditions. Herein, it is demonstrated that nitrogen and manganese depletion primarily reduced cell growth while phosphorus and iron restriction led to higher dry biomass. Subsequently, the role of those nutrients on fatty acids profile was examined. Phosphorus and nitrogen restriction resulted in lower and higher lipid content, respectively. High amounts of polyunsaturated fatty acids like eicosapentaenoic acid are produced under iron and manganese depletion. Phosphorus deprivation favors monounsaturated fatty acids such as C18:1 and C16:1, while nitrogen restriction favors saturated fatty acid production like C14:0, C16:0 and C18:0. Since the presence/absence of macro- and micro-elements may affect the overall electrostatic charges on the outmost microalgae surface, it was also analyzed how these elements affect the magnetic harvesting efficiency. Results showed that phosphorus deprivation led to the best magnetic harvesting efficiency of N. oceanica cells (93%) as compared to other nutrient starvation as well as standard medium.

Application of chemicals for enhancing lipid production in microalgae-a short review

Microalgae have attracted great attention as a promising sustainable resource for biofuel production. In studies aiming to improve lipid accumulation, many key enzymes involved in lipid biosynthesis were identified and confirmed, but genetic engineering remains a challenge in most species of microalgae. In an alternative approach, various chemical modulators can be used to directly regulate the lipid biosynthesis pathway, with similar effects to gene overexpression and interference approaches, including improving the precursor supply and blocking competing pathways. The produced lipid can be protected from being converted into other metabolites by the chemicals such as lipase inhibitors. In addition, a few chemicals were also demonstrated to greatly influence cell growth and lipid accumulation by indirect regulation of the lipid biosynthesis pathway, such as increasing cell permeability or regulating oxidative stress. Thus, adding chemical modulators can be a useful alternative strategy for improving lipid accumulation in large-scale cultivation of microalgae.

Accumulation of Lipids and Triglycerides in Isochrysis galbana Under Nutrient Stress

This study examines the relationship between the algal biomass as well as lipid and triglyceride contents in Isochrysis galbana and variation in nutrient culture conditions such as phosphorus concentration and iron concentration. From the selected experiments, a clear algal growth drop expressed by number of cells, optical density and dried weight, as well strongly participated in the lipid and triglyceride cumulation, which show a positive significant effect on lipid productivity and triglyceride productivity. In the first experiment of this study, the phosphorus concentration in the medium was reduced to 75%, 50%, and 25% and complete absence (0%) of the original concentration in Walne's medium, whereas the iron concentration was kept constant in the medium. The next experiment, the optimum phosphorus concentration (25%) granting high lipid product was tested with different concentrations of iron from 100 to 0% with five concentrations. Though, the algal growth nonsignificant affected, abundant increases in lipids and triglyceride contents (49.5% and 14.7% of dry weight respectively) was noticed at the concentration of phosphorus of culture medium was decreased to (25%). However, hyperaccumulations of lipid and triglyceride (60.3% and 18.4% on the basis of dry weight, respectively) were acquired by the incorporation of 25% phosphorus and 25% iron. The simple regression analysis suggested the combination effect of phosphorus limitation and iron deprivation on lipid and triglyceride cumulation, and it was not as substantial as to phosphorus starvation tension.

Physiological Changes of Parachlorella Kessleri TY02 in Lipid Accumulation under Nitrogen Stress

In order to study the effects of nitrogen stress on the lipid synthesis of Parachlorella kessleri TY02 and to understand the changes in growth, photosynthetic pigments, total protein and total carbohydrate contents during lipid accumulation, the cells of the strain were cultured in nitrogen-deficient (N⁻) and nitrogen-rich (N⁺) media for one week. Changes in cell growth, chlorophyll content, chlorophyll fluorescence parameters, neutral lipid and total lipid content, total protein content and total carbohydrate content were measured and analyzed. The results showed that, under nitrogen stress, the algal strain grew slowly, and chlorophyll and total protein contents decreased, while total carbohydrate and total lipid contents increased. This indicated that, under nitrogen stress, most of the carbon flowed to the synthesis of lipids and carbohydrates. Meanwhile, reducing the nitrogen content was a relatively economical and easy to operate method of promoting lipid accumulation.

Composition, Anti-inflammatory Activity, and Bioaccessibility of Green Seaweeds from Fish Pond Aquaculture

The nutritional composition was studied of green seaweeds ( Chaetomorpha linum, Rhizoclonium riparium, Ulva intestinalis, U. lactuca, U. prolifera) grown in fish pond aquaculture systems. Moreover, anti-inflammatory activities were measured. The effects of bioaccessibility on this property were assessed. There were qualitative differences in the lipid composition, since fatty acid profiles varied among seaweed species. Whereas U. lactuca and U. intestinalis fatty acid profiles were very similar, all other profiles differed significantly. U. prolifera was very rich in ω6 PUFA, while R. riparium was richer in ω3 PUFA. Concerning the ω3/ω6 ratio, the highest value was found for C. linum. The anti-inflammatory activity was higher for U. prolifera and C. linum with high cyclooxygenase-2 activity inhibition (ranging between 18 and 27 %) upon incubation of 100 μg/mL of these green seaweed extracts. Though the compounds causing this effect were not bioaccessible, U. prolifera seems to be a potential source of bioactive compounds.

An integrated salinity-driven workflow for rapid lipid enhancement in green microalgae for biodiesel application

A laboratory based integrated approach was undertaken for improvement of lipid accumulation in green microalgae under sodium chloride (NaCl) stress.