واکنش میزان رشد، محتوای پروتئین و اسیدچرب جلبک دسمودسموس کوناتئوس درشرایط کمبود و انباشتگی نیتروژن

نوع مقاله: پژوهشی- انگلیسی

نویسندگان

1 دانشگاه ارومیه، ایران.

2 دانشگاه ارومیه، ایران

چکیده

  مقدمه: میزان بیومس و محتوای بیوشیمیایی (به‏ویژه اسیدهای چرب، پروتئین و رنگدانه‏ها) جلبک‏های تک سلولی نقش مهمی را در تولید تجاری این میکروارگانیسم ایفا می‏کنند. نتایج پژوهش‏ها نشان داده هست که غلظت نیتروژن از عوامل مؤثر بر میزان رشد و ترکیب بیوشیمیایی جلبک‏های تک سلولی است.  
مواد و روش ‏‏ ها: در این پژوهش، ریز جلبک دسمودسموس کوناتئوس (خانواده سندسماسه، کلروفیتا) در محیط کشت BM ، دمای 25 درجه سانتی گراد و اسیدیته 7 تحت تأثیر غلظت‏های مختلف نیتروژن در یک دوره 12 روزه پرورش داده شد. به منظور تعیین تراکم سلولی و زمان دو برابر شدن جمعیت ریزجلبکی، شمارش جلبک‏ها به شکل روزانه و با استفاده از لام هموسیتومتری انجام گرفت. تعیین میزان اسیدهای چرب و پروتئین ریزجلبک‏ها نیز با برداشت توده جلبک در مرحله سکون انجام شد.  
نتایج: بالاترین میزان رشد ویژه (09/0 ± 35/0 در روز) و تراکم سلولی (105×01/1 ± 36 سلول در میلی‏لیتر) در غلظت 5/2 میلی‏مولار نیتروژن به دست آمد. همچنین، متوسط بیش‏ترین میزان اسیدهای چرب با چند پیوند غیراشباع، 31/25 درصد، در غلظت بالای نیتروژن (5 میلی‏مولار) و کم‏ترین مقدار، 01/17 درصد، در تیمار فاقد نیتروژن مشاهده شد. بیشینه میزان پروتئین، 81/35 درصد، نیز در غلظت 5 میلی‏مولار و کمینه آن، 14/11 درصد، تیمار فاقد نیتروژن به دست آمد.   بحث و نتیجه ‏ گیری: نتایج این مطالعه نشان داد که غلظت مواد مغذی مختلف نقش مهمی در پرورش ریز جلبک‏ها داشته و بسته به نوع مواد مغذی هر گونه کاهش یا افزایش در غلظت آن تغییراتی را در فیزیولوژی و ارزش غذایی ریزجلبک‏ها موجب می‏‏شود. در این مطالعه، غلظت 5/2 میلی‏مولار نسبت به سایر غلظت‏ها در عوامل مؤثر مورد مطالعه همانند میزان رشد نتایج بهتری نشان داد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Response of growth, protein and fatty acid content of Desmodesmus cuneatus to the repletion and depletion of nitrogen

نویسندگان [English]

  • Mehdi Naderi Farsani 1
  • Saeed Meshkiniy 2
  • Ramin Manaffar 2
  • Zahra Asal pishe 1
1 M.Sc. of Aquatic Cultivation and propagation, Urmia University, Iran.
2 Assistant professor of Fish higen, Urmia University, Iran
چکیده [English]

Introduction: Biomass and biochemical composition content (particular fatty acid profile, protein, Pigment) play an important role in commercial scale production of microorganisms. Nitrogen concentration is the most effective factor in biochemical composition and growth rate changes.
Materials and methods: The unicellular fresh water microalgae, Desmodesmus cuneatus (Scenedesmaceae, Chlorophyta), was grown on BM medium under various concentration of nitrogen at 25°C and pH 7.0in a period of 12 days. Daily cell counting was done using Neubauer haemocytometer to determine the growth rate, cell density and exponential time. The grown cells were harvested in the stationary phase to determine fatty acid and protein content.
Results: The maximum growth rate (0.35 ± 0.09day−1) and cell density (36.00 ± 1.01 ×105 cell.ml-1) was achieved in 2.5 mM of nitrogen concentration. The maximum level of PUFA, was 25.31% of the total fatty acids under N- sufficient conditions (5 mM nitrogen) compared to 17.01% under N- free. The maximum precentage of protein content (36.81%) was found at 5 mM nitrogen content and minimum (11.14%) was seen at nitrogen free medium.
Discussion and conclusion: The results showed that control of nutrients plays an important role in microalgae culture. Any increase or decrease, depending on the type of nutrient, causes metabolic changes as well as changes in physiology and the nutritional value of microalgae. The nitrogen concentration of 2.5 mM may be more beneficial than other concentrations, as cell number is sustained in exponential phase longer.

کلیدواژه‌ها [English]

  • Desmodesmus cuneatus
  • Fatty acid
  • Growth
  • Nitrogen
  • Protein

Introduction

Microalgae are classified under a varied group of photoautotrophic organisms which play important role as primary producers for feeding of zooplanktons and other animals in the food chain of aquatic systems. The ability of microalgae in production of bioactive compounds such as pigments, vitamins, proteins and fatty acids make them a good source to use them as bio energy and pharmaceutical resources in aquaculture systems (1, 2, 3 and 4). The growth and biochemical composition of microalgae is affected by culture conditions (5, 6 and 7). Microalgal cells have shown different mechanisms (such as enzyme reaction, cell permeability, and cell composition) to survive and optimize their growth in response to strong variations in physicochemical conditions (7 and 8). As a nutrient, nitrogen is required in high concentration and is counted as one of the most important chemical nutrients that require microalgae growth. After carbon, nitrogen plays the second important role in production of biochemical compounds such as amino acids, nucleic acids and other nitrogen- enriched molecules in the grown microalga biomass. In recent years, the importance of nitrogen in microalgae biomass has been studied by many researchers (9, 10 and 11). In normal condition, the chlorophyll accumulation and cell division is. In contrast, depletion of nitrogen resources result in the changes in some biosynthesis pathway of microalgae such as a decline in nitrogenous photosynthetic pigments, reduction in photosynthetic efficiency, cell division prevention, lower growth rate, and a reduction in cell size (12 and 13). Further, nitrogen limitation leads to accumulation of carbon compounds such as polysaccharides, fats and reduction of carbohydrate production. Moreover, differences in fatty acid profile occurring response to various nitrogen concentrations (14 and 15). The nitrogen limitation also resulted in the higher saturation in lipid profiles (increase in C18:1, and decrease in C18:2 and C18:3) and fatty acid reduction (13 and 16). Numerous studies have shown different concentrations of nutrients that have a wide effect on the biochemical composition, growth and morphology of fresh water algae (12 and 17). Nitrogen starvation and limitation, on the other hand, cause very different nitrogen stresses which may lead to various physiological responses.

The green algae D. cuneatus is a chlorococcal coenobial (Scenedesmaceae, chlorococcales, chlorophyta) which is widely distributed in freshwaters with moderate temperature. The green algae are highly polymorphic (18). Accordingly in this study, the influence of different nitrogen concentrations on fatty acid profile, total protein, growth rate and chlorophyll content of Desmodesmus cuneatus was investigated.

 

Materials and methods

Desmodesmus cuneatus was obtained from algae bank Artemia and aquatic research institute, Urmia, Iran. Experiments were performed on culture of 450 ml, grown in 500 ml glass flasks. All the glassware and media were sterilized prior to inoculation. Culture was grown in BM medium (Table 1) (19). Stock culture of D. cuneatus was performed at 25°C under continuous fluorescent illumination (100 μmol photons m-2 s-1) and pH 7.5.

Table 1- The content of BM medium

Constituents

 (mg.l-1)

KNO3

100

MgSO4.7H2O

40

Cl2Co.6H2O

0.110

MnCl2.4H2O

0.108

Na2MoO4.2H2O

0.0075

ZnSO4.7H2O

0.066

FeCl3.6H2O

5.88

Ca (NO3) 24H2O

150

β- Na2 glycerophosphate

50

EDTA- Na2

2.27

Biotin

0.1

Thiamine- HCL

0.01

Trisaminomethane

0.5

 

Stress conditions

Initial density for D.cuneatus was set on 3.2 × 105 algal cells. Cultures of cells were washed in double- distilled water (DDW) and resuspended in the medium with different concentrations of nitrogen (KNO3) (5 mM, 2.5 mM, 1.25 mM, 0.62 mM and nitrogen free medium).

In order to assess the cell densities during culture period, cells were daily counted using a haemocytometer. Growth rates and doubling time (DT) were calculated on cell basis which were calculated based on following equation Guillard and Omori.

μg (day-1) = (Ln (n2/n1) /t2-t1); (20)DT = loge2/µ (21)

Where μ is the specific growth rate, N2 and N1 are biomass concentrations at the start (t1) of exponential phase (cell.ml−1) and at the end of experiment (t2) respectively.

In order to determine chlorophyll a and b, 5ml acetone was added to each tube containing 5ml of culture and then filtered (using GF/C filters). Each sample was maintained in the dark at 4°C for 24 h, then cells were broken using an ultrasound (on ice) up to 90s and subsequently centrifuged at 12, 000×g for 5 min. Chlorophyll a and b was determined using the equation based on the method of Ritich (22).

Total protein was extracted according to Meijer and Wijffels' method (23). First 500

ml of the algal sample was centrifuged at 4°C at 500 g for 10 min, washed and centrifuged again and then freeze–dried. For protein analysis, 20 mg aliquots of the freeze–dried biomass were suspended for 20 min in 10 ml of lysis buffer in a Falcon tube and then resuspended in 10 ml phosphate buffer with 1% (w/v) SDS (sodium dodecyl sulfate) to facilitate the extraction of proteins. Total protein was determined by means of the method of Bradford, using bovine serum albumin standards (24).Quantitive measurement of fatty acids was performed using GAS chromatography (Agilent 6890 Gas Chromatography device) according to the method of Cohenet al. (25). Accordingly, Biomass was transmethylated with 2% H2SO4 in the dry methanol/toluene mixture (90:10, v/v) at 80°C for 1.5 h and heptadecanoic acid was added as an internal standard. FA methyl esters were determined by co- chromatography with authentic standards (Sigma) and by comparison of their equivalent chain length (26).

The SDS- PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) method was used for total protein analyses of Algae samples (27).

Two hundred milligrams of each sample were prepared for SDS- PAGE in liquid nitrogen and pulverized in 1.5 ml microtube by appropriate tips. Fifty milligrams of the resulting powder were transferred into 500 μl of protein extraction buffer (buffer K). The extraction buffer for SDS- PAGE contained: 5 mM MgCl2, 5 mM nitrogen H2PO4, 40mM Hepes, 70mM Potassium gluconate, and 150mM Sorbitol, and pH was set at 6.5 containing a protease inhibitor cocktail (Invitogene™ Mini from Roche Diagnostics GmbH) (28). Protein concentration was determined by the Bio photometer apparatus (Eppendorf). Samples were heated for 5 min at 95° C and subsequently cooled to room temperature in tap water. After low speed centrifugation (1600 g, 5 min) to remove insoluble fragments, supernatants were electrophoresed. Proteins were separated by 12.5% SDS- PAGE (27). Each lane was loaded with 15 μg total proteins run at 200 V for 45 min. Protein bands were stained with 0.125% Coomassie Brilliant Blue R- 250 in 40% methanol, 10% acetic acid for 1 h at a 50°C water bath with gentle agitation. Destaining was performed in 5% methanol, 7.5% acetic acid for 2 h at 50°C with gentle agitation.

The obtained growth rate data were analyzed by one- way ANOVA. Tukey’s test was performed to identify differences among the means, and differences were considered statistically significant at Pvalue

 

Results

The effect of five level of nitrogen concentrations on the growth of D. cuneatus was investigated for 12 days. The effect of nitrogen concentration was monitored by counting the cells number of D. cuneatus (Fig. 1). Based on Fig. 1, during stress, lowest growth rate (0.23 ± 0.06 μgday−1) was observed in the nitrogen free treatment group. On the other hand, maximum specific growth rates (0.35 ± 0.09 μgday-1) and (0.33 ± 0.09 day−1), were observed in groups treated with 2.5 mM nitrogen and 5 mM nitrogen, respectively (Table 2). In 1.25 mM nitroge, the maximum growth rate (0.29 ± 0.05 μgday−1) was observed with density of 22.72× 105 cells ml−1 (Fig. 1). In 0.62 mM nitrogen, the maximum growth rate was 0.27 ± 0.07 μgday−1 (Table 2).

 

 

 

 

Fig. 1- Cell number of D. cuneatuscultured under different nitrogen concentrations

 

Table 2- Cell number of D. cuneatuscultured under different nitrogen concentrations

N concentration

 (mM nitrogen)

Maximum density

 (*105 cells.ml-1)

Growth rate,

μgday-1 (d-1)

Doubling time (d-1)

5

31.51 ±0.68 a

0.33 ± 0.09a

2.14

2.5

36.00 ± 1.01b

0.35 ± 0.09a

1.98

1.25

22.72± 0.87c

0.29 ± 0.05b

2.39

0.62

17.50 ± 0.86d

0.27 ± 0.07b

2.56

0

12.11 ± 0.47 e

0.23 ± 0.06 c

3.01

Values sharing the same letter in each row are not significantly different, ANOVA; P value>0.05

 

Table 3- Chlorophyll α, b and protein contents of D. cuneatus cultured under different nitrogen concentrations

Concentration mM ntrogen

chl α mg.l-1

chl b mg.l-1

Protein (%)

5

8.01 ± 1.04 a

6.23 ± 0.43a

36.81± 1.53 a

2.5

7.11 ± 1.44 ab

5.11 ± 0.42 b

22.13 ± 2.11 b

1.25

6.41 ± 0.78 ab

4.51 ± 0.86 b

18.08± 3.14 c

0.62

4.62 ± 0.55 c

2.1± 0.57 c

19.23± 1.71 c

0

2.1 ± 0.89 d

1.3± 0.92 c

11.14± 2.53 d

Values sharing the same letter in each row are not significantly different, ANOVA; P value <0.05

 

 

High pigment values probably attributed to the high cell density. Content of chlorophyll α and b significantly varied (Pvalue<0.05) under various nitrogen concentrations. The maximum (8.01 mg.ml−1) and the minimum (2.1 mg.ml−1) chlorophyll a content were measured at 5 mM nitrogen and nitrogen free respectively (Table 3). The chlorophyll b content of the cells also was affected by different nitrogen concentrations. The maximum chlorophyll b (6.23 mg.l-1) was measured at 5 mM nitrogen, while the minimum (1.3 mg.l-1) was observed at nitrogen free treatment (Table 3). Different nitrogen concentrations positively affected protein content (Table 3). The maximum protein concentration was 36.81% at 5 mM nitrogen, and the minimum was 11.14% at nitrogen free.


D. cuneatus showed significant differences in total protein content at various level of nitrogen concentration (Fig. 2). A major protein of approximately 68 kDa was observed in stress conditions. In addition, several proteins with molecular weight of approximately 36, 48 and 60 kDa were observed in 5 and 2.5 mM of nitrogen concentration treatments (Fig. 2).

 

 

Fig. 2- SDS- PAGE gel electrophoresis of D.cuneatus cultured under different nitrogen concentrations

The fatty acid composition of D.cuneatus was measured in stationary phase of the cultured cells at different nitrogen concentration levels (Table 4). The most abundant saturated fatty acid was 16:0 (palmitic acid), which constituted 26.01% of the total fatty acids at the nitrogen free treatment. Among the PUFAs, 18:3 (n–3) was the major fatty acid (by 13.51%) of the total fatty acids. The total percentage of PUFA (Polyunsuturated fatty acids) decreased at low nitrogen concentration, so the minimum percentage of PUFA (17.01%) was observed at the nitrogen free treatment group. In contrast, the highest percentage of the PUFA (25.31%) was recorded at the maximum nitrogen concentration (5 mM nitrogen). As for SFA (Saturated fatty acids) and MUFA (Monounsaturated fatty acids), highernitrogen concentration was associated with low percentage of these groups of fatty acids. The maximum percentages of MUFA (22.10 and 23.00%) and SFA (29.89 and 31.54%) were observed at 0.62 mM nitrogen and nitrogen free respectively.

 

 

 

 

Table 4- Fatty acids (mean ± SD %) (Expressed on the percentage of total fatty acids) of D. cuneatuscultured under different nitrogen concentrations

Fatty acid

5 mM

nitrogen

2.5 mM nitrogen

1.25 mM nitrogen

0.62 mM nitrogen

free

nitrogen

C14:00

0.64 ± 0.08b

0.32 ± 0.09b

1.43 ± 0.06a

0.48 ± 0.02b

0.26 ± 0.01b

C16:0

21.99 ± 0.20c

22.81 ± 0.33c

24.64 ± 0.90b

25.72 ± 0.22ab

26.01 ± 7.42a

C18:0

0.61 ±0.41c

1.16 ± 0.16a

0.51 ± 0.06d

1.01 ± 0.13b

0.98 ± 0.09b

C20:0

0.56 ± 1.84c

0.92 ± 0.07b

0.24 ±.04d

0.91 ± 0.01b

1.15 ± 0.37a

C22:0

1.51 ±2.15a

1.64 ± 0.13a

1.8± 0.02a

1.53 ± 0.06a

2.1 ± 0.19a

C24:0

0.64 ± 1.14b

0.17 ± 0.01c

0.22 ± 0.22c

0.24 ± 0.24c

1.04 ± 0.04a

SAF

25.95 ± 0.76c

27.02 ± 1.06c

28.84± 0.97b

29.89± 1.22b

31.54 ± 0.66a

C14:1n5

2.10 ± 0.71ab

2.71 ± 0.06a

2.83 ± 0.01a

1.07 ± 0.05c

1.40 ± 0.10bc

C16:1n7

0.37 ± 0.33b

0.51 ± 0.01b

1.15 ± 0.03a

0.36 ± 0.03b

0.12 ± 0.01b

C18:1n9

6.76 ± 0. 58c

7.90 ±2.42b

8.34 ± 0.40b

10.35 ± 1.02a

10.64 ±0.02 a

C18:1n7

10.12 ±0.79a

9.75 ± 1.10a

7.45 ± 0.11b

9.35 ± 0.11a

10.39 ± 0. 79a

C20:1n9

0.15 ±.09d

0.43 ± 0.03c

0.79 ± 0.04a

0.64 ± 0.01b

0.15 ± 0.15d

C22:1n9

-

-

-

-

-

C24:1n

0.24 ± 0.09c

0.1 ± 0.03d

0.51 ± 0.02a

0.33 ±.02b

0.3 ± 0.04bc

MUFA

19.74 ± 0.66c

21. 4 ± 0.46b

21.07 ± 0.33b

22.10 ± 0.82ab

23.00 ± 1.1a

C18:2n6

10.7 ± 1.13a

7.81 ± 0.26b

7.50 ± 0.82b

6.61 ± 0.23b

4.79 ± 0.26c

C18:3n3

10.45 ± 0.74b

13.51 ± 0.02a

12.92 ± 0.23a

10.52 ± 0.03b

8.52 ± 0. 46c

C20:2n6

-

-

-

-

-

C20:4n6

-

-

-

-

-

C20:3n3

3.01 ± 2.10a

1.29 ± 0.04bc

0.28 ± 0.02c

1.29 ± 0.14bc

2.32 ±.10ab

C20:5n3

0.83 ± 0.08ab

0.04 ± 0.02b

0.21 ±0.07b

0.34 ± 0.03b

1.22 ± 0.19a

C22:6n3

0.32 ± 0.32a

0.07± 0.07a

0.09 ± 0.02a

0.34 ± 0.01a

0.16 ±0.16a

PUFA

25.31 ± 0.29a

22.72 ± 0.96b

21.00 ± 0.53c

19.1 ± 0.76c

17.01 ± 1.12e

Values sharing the same letter in each row are not significantly different, ANOVA; P value>0.05

 

 

 

 

 

Discussion and conclusion

Total biomass, quantity and quality of biochemical composition particular fatty acid profile, protein and pigment content, play an important role in commercial scale production of microalgae. Changes in nitrogen concentration have been led to significant differences in pigment and growth rate (29 and 30). The present study has also proved significant differences in the growth rate of D. cuneatus cultured under various levels of nitrogen concentrations. The biomass concentration was increased as nitrate source increased in the medium (5 and 2.5 mM nitrogen), in (Fig. 2). This result is the same as the results of Banerjee who found the growth rate in D. cuneatus declined under limited nitrogen sources (31). Similarly, some previous studies showed decreasing trend in growth rate for many microalgae culture under low concentration of nitrogen (15 and 32). Yeesang and Cheirsilp reported loss of biomass when green alga Botrycoccus sp. was exposed to deficient nitrogen (33). Li et al. noticed that the growth rate in Pavlova viridis decreased in the nitrogen- free medium while it increased in nitrate- rich media (34). Decrease in algal biomass concentration in low nitrate concentration was also observed by Hu and Gao in Nannochloropsis sp. (35). Studies also indicated that in nitrogen free medium, cells start to metabolize pigments to release nitrogen (34).

We found that the chlorophyll α and b content was increased at high nitrogen concentration (5 and 2.5 mM nitrogen). On the contrary, the chlorophyll α and b value was decreased in algae cultivated at low nitrogen concentration (0.62 mM nitrogen and free N). This result is similar to the findings of Ördög et al. who noted that high nitrogen concentration (70 and 700 mg. L−1N) led to increase in the chlorophyll α and chlorophyll b contents (36). In contrast, carotenoid concentrations gradually declined. Similarly in Neochloris oleoabundus, there was a decrease in chlorophyll α within 2 days and day 4 in low- nitrogen and intermediate nitrogen treatments, respectively. However there was no decrease in higher nitrogen treatment (14). The changes in pigments content are considered to be an adaptation mechanism to various nitrogen concentrations, so in the higher nitrogen concentration, chlorophyll is utilized for faster growth rates and in depleted nitrogen concentration, chlorophyll was degraded to support cell growth and biomass production (14 and 36). The total protein showed a strong positive relationship with nitrogen concentration. The total protein production increased within high nitrogen concentration and minimum percentage of protein content was observed at lower nitrogen concentration (Table 3).

li et al. noted that increase in nitrogen concentration caused increase in protein biosynthesis and low nitrogen concentration led to protein decline in Pavolva viridis (34).Various species of microalgae shows different responses to the nitrogen stress. For example, Chlorella vulgaris and C. minutissima have shown large decrease in protein content in response to nitrogen stress (36 and 37). Whereas, Dean et al. concluded that the protein content in Chlamydomonas reinhardtii and Scenedesmus subspicatus showed a minimal change in response to nitrogen limitation (38). Also under nitrogen limitation, carbon reallocation resulted in a decrease in cellular protein such as Rubisco and an increase in lipids (16, 39 and 40). Several groups of proteins with different molecular weigth were accumulated under nitrogen stress condition. The most abundant protein in our study was a 68 kDa protein; while in Haematococcus pluvialis growing under low and high nitrogen concentration, proteins with molecular weigth of 38kDa- 63kDa were accumulatedin the cultured cells. Conversely, in nitrogen starvation condition, proteins with molecular weigth of approximately 28kDa were accumulated in Chlamydomonas reinhardtii (41).

Changes in fatty acid composition in microlagae have been previously reported in response to changes in nitrogen concentration (4, 17, 30, 34 and 42). We detected 17 fatty acids in D. cuneatus and observed that cellular content of fatty acids ranged from 0.07 to 26.01% in different treatments. In the present study, as nitrogen concentration increased, the ratio of the total saturated and monounsaturated fatty acids decreased, and in turn the polyunsaturated fatty acids increased. Maximum PUFA contents were found at high nitrate concentration (5 mM nitrogen). This result is similar to the findings of Chu et al. (42). Similar to Li et al. who reported the increasing level of saturated and monounsaturated fatty acids in nitrogen depletion condition of Pavolva viridisculture (34). In Nannochloropsis sp., the response to nitrogen starvation was a decrease in polyunsaturated fatty acids and an increase in the saturated FA (15). Other studies have found that nitrogen limitation alters the lipid profile towards higher saturation (increase in C18:1, and decrease in C18:2 and C18:3) and further reduction in fatty acids chain (13 and 16). The effect of nitrogen on the cellular fatty acid composition seems to be quite complex and appears to be different according to species. For example, Hu and Gao showed that both low and high nitrate conditions resulted in higher amount of EPA on a dry- mass basis (35), whereas Parietochloris incisa revealed increase in arachidonic acid at lower nitrogen level (9). li et al. reported the highest EPA content in total fatty acids at the maximum nitrate (6.2 mM) (34). Thompson noted that under nitrogen deficiency, many microalgal species accumulate lipids mostly TAG (triacylglycerols) which generally contain saturated and monounsaturated fatty acids (43).

The results showed that control of nutrients plays an important role in microalgae culture. Any increase or decrease, depending on the type of nutrient, causes metabolic changes as well as changes in physiology and the nutritional value of microalgae. The nitrogen concentration of 2.5 mM nitrogen may be more beneficial than other concentrations, as cell number is sustained in exponential phase longer.

 

Acknowledgment

The authors are grateful to the manager and staff of Artemia and aquatic research institute (West Azarbijan Province) who kindly cooperated with us throughout the study, and Urmia University for the financial support.

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