EFFECT OF NITROGEN, PHOSPHORUS CONCENTRATIONS, pH AND SALINITY RANGES ON GROWTH, BIOMASS AND LIPID ACCUMULATION OF CHLORELLA VULGARISHTML Full Text
EFFECT OF NITROGEN, PHOSPHORUS CONCENTRATIONS, pH AND SALINITY RANGES ON GROWTH, BIOMASS AND LIPID ACCUMULATION OF CHLORELLA VULGARIS
Neha Kalla* and S. Khan
Department of Bioscience and Biotechnology, Banasthali University, Rajasthan, India
ABSTRACT: Microalgal like Chlorella vulgaris, being a unicellular green algae, is been widely studied for nitrogen and phosphorus removal and as potential feedstock for biodiesel production. This not only saves water from eutrophication but also becomes a good source of biodiesel. Hence, if two approaches are combined we can overcome the major challenge of both eutrophication and energy crisis. In the present study we have examined the effect of decreasing Nitrogen and phosphorus concentration in medium on growth, biomass and lipid content of C. vulgaris. Significant decrease in growth and biomass was observed with the decrease of nitrogen and phosphorus concentration in the medium from (1.5g/l to 0.0g/l) and (0.04g/l to 0.0g/l) respectively. Whereas the lipid accumulation showed reverse trend of increase when the concentration of both phosphorus and nitrogen where decreased in medium. At the same time, the effect of variation in pH and saline ranges on growth, biomass and lipid content of C.vulgaris were also evaluated. The growth, biomass and lipid content showed a significant difference due to the variation in pH and saline range. The growth and lipid content was maximum at control range i.e pH 7 with respect to 6, 8 and 9. On the other hand we could see that with the increase of salinity from 0.1M to 0.25 M the growth decreased whereas the lipid content showed an increasing trend.
Chlorella vulgaris, Microalgae, Growth, Biomass, Lipids, Nitrogen, Phosphorus, pH, Salinity, Biomass
INTRODUCTION: Microalgae are unicellular photosynthetic organisms which use light energy and carbon dioxide for production of biomass. The biomass produced can be used for various application, some are extraction of high rate value foods such as γ-linolenic, arachidonic acid, eicosapentaenoic and docosahexaenoic acids 1, 2, 3, and food for aquaculture, pharmaceutical products, and biofuel productions 3, 4.
There will a substantial change in quality and quantity of lipids within the cells and they vary as a result of changes in growth conditions (light, temperature etc.) or nutrient media characteristics (concentration of Nitrogen, Phosphorus and Iron) 5, 6, 3. Biodiesel which is now widely accepted as the alternative to standard diesel and Algae is one of the promising source for biodiesel production 7. Triacylglycerol (TAG’s) are the sustainable feedstock for biodiesel production, photosynthetic microorganisms that convert water, sunlight and CO2 to sugars from which macromolecules such as lipids and TAG’s can be obtained 7, 8.
Intensive research and development on several aspects is needed for commercial production of biodiesel. The optimization of selected strains is required for biomass production and lipid profile 9, 7. There are quite a few species of microalgae which have high content of oil and can be manipulated to produce more oil 10, 7. Many researchers have proved that lipid tend to accumulate in nutrient deficient (nitrogen and phosphorus) conditions.
Nitrogen is an essential constituent of all structural and functional proteins in the algal cells and accounts for 7% - 20 % of cell dry weight 11, 12. Nitrogen deficiency in algal culture enhances the biosynthesis and accumulation of lipids 13, 3, 14, 15, 16, 12 and triglycerides 17, 18, 12. The limitation of nitrogen can be considered as an efficient environmental pressure to enhance lipid accumulation 19, 20, 21. Other effects of nitrogen reduction are Carbon dioxide fixation, decrease in oxygen evolution, Chlorophyll content and tissue production 22, 23, 12.
Other than Nitrogen, Phosphorus is important component required for normal growth and development of algal cells 11, 12. It is studied that 1% of dry weight of algae is constituted by phosphorus 25, 12. Effects of phosphorus limitation include a reduction in the synthesis and regeneration of substrates in the calvin – benson cycle and a consequential reduction in the rate of light utilization required for carbon dioxide fixation 23, 12.
The research has been done on many algal species for biodiesel production. Chlorella was selected as test organism as it has great potential to be a resource for biodiesel production due to its fast growth and easy cultivation. However, lipid content in Chlorella under general growth conditions is 14-30% by weight of dry biomass 4, 5. Certain culture conditions could result in higher quantities of lipids to find if these could promote the biomass productivity or lipid accumulation under lab conditions, the effect of nutrients and other growth parameters such as pH values and salinity ranges viz. on growth and lipid content in marine strain Chlorella vulgaris should be investigated comprehensively to further validate this study.
This study is conducted to investigate the growth response, biomass and lipid content of C. vulagris by varying the concentration of Nitrate NaNO3, Phosphorus K2HPO4, pH and salinity ranges.
MATERIAL AND METHODS:
Culture conditions: Established cultures of the green microalgae C. vulgaris were grown in 150 ml Erlenmeyer flasks containing 50 ml BG11 medium at pH 7.0 in a culture room at 25 ± 2º C under a photoperiod of 14 : 10 h at light intensity of 75 μmol photonm−2 s−1 PAR without sparging with air or CO2.
The mineral salt medium composition per liter of distilled water was as follows:
Macronutrients: 1.5g NaNO3, 0.04g K2HPO4, 0.075g MgSO4.7H2O, 0.036g CaCl2.2H2O, 0.006g Citric Acid, 0.006g Ferric Ammonium Citrate, 0.001g EDTA ( Disodium magnesium salt) and 0.02g Na2CO3.
Micronutrients: 2.286mg H3BO3, 1.81mg MnCl2.4H2O, 0.222mg ZnSO4.7H2O, 0.039mg Na2MoO4.2H2O, 0.079mg CuSO4.5H2O, 0.0494mg Co(No3)2.6H2O. pH was set between 7.0-7.5.The cultures were hand shaken two or three times daily to avoid sticking. This was referred to as control culture.
Optimization of medium on different Nitrogen, Phosphorus, pH and Salinity ranges:
The one set of triplicates of cultures for evaluation were grown in 150 ml Erlenmeyer flasks containing 50 ml BG11 medium on different Nitrogen concentrations (NaNO3 as nitrogen source at 1.5 g/l, 0.75 g/l and 0.375 g/l and 0.0 g/l respectively and NaNO3 replaced by NaCl), and another set of triplicates for different phosphorus concentration (K2HPO4as phosphorus source at 0.04 g/l, 0.02 g/l, 0.01 g/l and 0.0g/l respectively and K2HPO4replaced by KCl) the pH was set at 7.0.
At the same time two set of triplicates of cultures were also grown on optimized medium at various ranges of pH (6.0–9.0 at an interval of 1.0) and salinity ranges (0.1M–0.25M at an interval of 0.05, for saline cultures the pH was set at 7.0). All cultures were kept in a culture room at 25 ± 2º C under a photoperiod of 14 : 10 h at light intensity of 75 μmol photonm−2 s−1 PAR without sparging with air or CO2.
Growth Analysis: Algal growth was measured on regular intervals (7, 14, 21 and 28 day respectively) by recording the changes in optical density at 663nm with a spectrophotometer.
Dry cell weight measurement: Dry cell weight (dcw) was determined by gravimetrical method 26. A known volume of algal culture was centrifuged at 5000 rpm for 15 min and the harvested biomass was dried at 80◦C to constant weight.
Extraction and Estimation of lipid from algal biomass:
Extraction of lipid was done following the protocol of Bligh and Dyer (1959) 24. To a 15 ml glass vial containing a known amount of algal biomass, 2 ml methanol and 1 ml chloroform were added and kept for 24 h at room temperature. The mixture was agitated in a vortex for 2 min, and 1 ml of chloroform was again added and the mixture shaken vigorously for 1 min; 1.8 ml of distilled water was added and the mixture was agitated in a vortex again for 2 min. The layers were separated by centrifugation for 10 min at 2000 rpm. The lower layer was filtered through Whatman No. 1 filter paper into a previously weighed clean vial (W1). Evaporation was carried on in a water bath and the residue was further dried a 104ºC for 30 min. The weight of the vial was again recorded (W2). Lipid content was calculated by subtracting W1 from W2, and was expressed as % dcw.
All the experiments were performed in triplicates, the results were analyzed statistically by SPSS PASW 18.0 for two ways Anova and Tuckey's test.
RESULT AND OBSERVATION:
Effect of Nitrogen on Growth and Biomass:
The time course of C.vulgaris culture growth under the effect of reduction of NaNO3 concentration is shown in Fig.1 (A). The concentration of nitrate NaNO3 was reduced to half and quarter of standard medium whereas in one medium NaNO3 was deficient and in another NaNO3 was replaced by NaCl.
FIG. 1: EFFECT OF VARIABLE NITROGEN CONCENTRATION ON GROWTH, BIOMASS AND LIPID CONTENT OF CHLORELLA VULGARIS
The growth was significantly affected; maximum algal density was observed in control culture (1.5 g/l NaNO3). On day 28th 54 fold increase from zero days was observed in control culture. The growth showed decrease as NaNO3 in medium was reduced from 0.75 g/l NaNO3, 0.375 g/l NaNO3, 0.0g/l NaNO3 and NaNO3 replaced by NaCl. An increasing trend was observed from zero days to 21st day after which a stationary phase was attained on 28th day.
The biomass yield also showed a similar trend like growth. This is depicted in Fig.1 (B). The maximum biomass with respect to zero days showed highest increase on day 28th with 115 fold increases in control culture, minimum biomass was observed in 0.0g/l NaNO3 medium and medium with NaNO3 replaced by NaCl with only 25 and 23 fold increase respectively from zero days to 28th day.
Effect of Nitrogen on Lipid Content:
An additional investigation was carried out to study the effect of reduction and limitation of NaNO3 concentration in medium on Lipid pool of C.vulgaris. This is depicted in Fig. 1 (C). The results showed a very significant (P < 0.05) increase in lipid content with decrease in NaNO3 concentration. The culture growing in 0.375 g/l NaNO3 showed 2 fold increases in lipid content with respect to control culture (1.5 g/l NaNO3). The culture growing in 0.0g/l NaNO3 medium resulted in 3 fold increase in lipid pool, whereas the most significant increase of 10 folds was observed in culture growing in medium in which NaNO3 is replaced by NaCl.
Effect of Phosphoruson growth and biomass:
Fig.2(A) shows the result of experiments conducted at varied phosphorus limitation and deficiency resulted in significant (P<0.05) increase in growth, biomass and lipid content. The growth significantly increased from zero day to 21st day on day 28th stationary phase was attained maximum growth was observed in control culture (0.04 g/l K2HPO4) with 42 fold increase from zero day. On day 28th minimum growth was observed in 0.0 g/l K2HPO4 and medium with K2HPO4 replaced by KCl with only 2 fold and 3 fold increase respectively from zero days.
FIG.2: EFFECT OF VARIABLE PHOSPHORUS CONCENTRATION ON GROWTH, BIOMASS AND LIPID CONTENT OF CHLORELLA VULGARIS
Fig.2 (C) showed increase of biomass from zero days to 21st day and stationary phase was attained on 28th day with no further increase in biomass. Maximum biomass yield of 113 fold with respect to zero days was observed in control (0.04g/l K2HPO4) and it reduced as phosphorus concentration was decreased. Minimum yield of 41 fold with respect to zero days was observed in medium in which K2HPO4 was replaced by KCl.
Effect of Phosphorus on Lipid Content:
Furthermore, investigation was also carried out to study the effect of reduction and limitation of phosphorus concentration in medium on Lipid pool of C.vulgaris. As shown in Fig. 2 (B), Lipid content in C.vulgaris showed significant increase with number of days of incubation. Lipid pool increased from zero days to 28th day. As K2HPO4 concentration was decreased the lipid content increased. Minimum lipid content was observed in control culture (0.04 g/l K2HPO4). Maximum lipid yield was observed in culture deficient with K2HPO4 (0.0g/l K2HPO4) with 4 fold increase from control culture and in culture where K2HPO4 was replaced by KCl with 6 fold increase from control culture.
Effect of varied pH:
The Growth curve of C.vulgaris is shown in Fig. 3 (A), the maximum algal density was statistically significant (P < 0.05) in control culture (pH 7) with respect to pH 6, 8 and 9. In all the cultures with variable pH marked increase from 7th day to 21st day was observed and decline in algal density was seen on day 28. The control culture with pH 7 showed 39.9% increase from culture with pH 6, 53% increase from culture set on pH 8 and 56% increase from culture set on pH 9 on day 21. Day 28 exhibited a marked declining trend. In control culture (pH 7) Algal density exhibited increase of 83% from 7day to 21 day. Experiments were performed in triplicates under optimized conditions to determine the biomass yield, presented in Fig.3 (B), the most significant increase in biomass yield to 87.5 % was obtained in control culture on day 21. As compared to pH 6,8and 9 control culture showed statistically significant (P < 0.05) biomass yield. pH 7 and pH 6 showed difference of 53.7% whereas pH 8 and pH 9 in comparison to control culture showed 57.4% and 62.8% difference respectively on day 7. The biomass yield kept on increasing till day 21st after that no further increase was observed.
FIG.3: EFFECT OF VARIABLE pH RANGES ON GROWTH, BIOMASS AND LIPID CONTENT OF CHLORELLA VULGARIS
Effect of pH on Lipid Accumulation:
Experiments conducted at varied pH to study lipid accumulation in C.vulgaris resulted in increase/decrease in lipid yield with respect to control (pH 7) shown in Fig.3(C). pH 6 showed decrease in lipid pool with respect to pH 7. Lipid yield showed increase of 124 folds and 178 folds respectively in pH 8 and pH 9 on day 21 and decline was observed on day 28.
Effect of Salinity on Growth:
The growth curve of C. vulgaris with respect to variable saline ranges is shown in Fig.4 (A). We can conclude that growth differs significantly (P < 0.05). Tukey’s post-hoc analysis suggests that control culture showed maximum growth and it decreased as salinity in medium was increased from 0.1M to 0.25M. The 46.1 fold increase was observed on day 21st in the control culture with respect to zero days. In all the mediums with variable salinity range the increasing trend of growth was observed from zero day to 21st day after which decline was observed on 28th day. Lowest growth was observed in culture with 0.25M salinity, an increase of 16.9 fold was observed with respect to zero day on day 21st. The biomass also statistically significant (P < 0.05) showed similar trend as shown by the growth i.e highest biomass was observed in control culture and minimum in culture growing in 0.25 M saline medium as shown in Fig. 4 (B). The increasing trend was observed from zero days to 28th day. Highest 87 fold increase was observed in control culture on day 28th. 0.25 M saline culture showed only 52 fold increase with respect to zero days.
Effect on Lipid Content:
The lipid accumulation in C. vulgaris at different saline ranges was studied in triplicates under optimized conditions and it differed significantly (P < 0.05). The highest lipid yield was observed in culture growing in 0.25 M saline medium and lowest was observed in control culture (0.0M saline medium) as shown in Fig.4 (C).
The yield increased from zero days to 28th day. On 2th day 91 fold increase was observed in 0.25 M saline culture with respect to 81 fold, 72 fold, 66 fold and 42 fold increase in 0.2M, 0.15 M, 0.1 M and control culture i.e 0.0 M respectively.
FIG. 4: EFFECT OF VARIABLE SALINITY RANGES ON GROWTH, BIOMASS AND LIPID CONTENT OF CHLORELLA VULGARIS
DISCUSSION: It has been reported that unfavorable conditions like deficiency of minerals (Nitrogen and phosphorus) nutrition in many unicellular green algae impacts growth and biomass and promotes biosynthesis of lipids. Variation of biochemical composition is observed in algae and it depends upon which nutrient is limited and to what degree 12.
The two major macronutrients for growth and metabolism of algal cells are nitrate and phosphates. Nitrogen is major element for formation of protein and nucleic acid whereas phosphorus is important part of backbone of DNA and RNA. Limitation and deficiency of these key nutrients shifts the metabolic pathway of microorganism 12.
The experiment conducted to study growth, Biomass and lipid pool of C. vulagris with variable nitrogen and phosphorus in medium showed that with decreasing nitrogen and phosphorus growth and biomass decreased but on the other hand we observed the enhanced biosynthesis and accumulation of lipids and TAGs 13, 3, 14, 15, 16, 17, 18, 28, 12 and reduction of protein content 29, 30, 28, 31 12. One of the reasons stated by 32 is that under nitrogen limitation NADPH consumption decreases due to unavailability of nitrogen pool thus there is excess NADPH in cells 32, 33. This result in an increase in pool of acetyl CoA which could not enter TCA cycle due to high concentration of NADPH which inhibit the enzyme citrate synthase 32, 34. Acetyl CoA might then be converted into mallonyl CoA catalyzed by acetyl CoA corboxylase (Accase) the central carbon donor for fatty acid synthesis 32, 35. Phosphorus limitation also leads to accumulation of lipids 12. Still further investigations are required to know how phosphorus limitation works to enhance lipid pool.
The sudden change in growth conditions and stresses like deficiency of nutrients or high salinity in some algae has significant impact on growth biomass and lipid yield.
The experiments conducted to study growth of C.vulgaris with variable pH showed that maximum growth occurs at control pH 7 as the pH was increased to 8 and 9 the decrease in algal density was observed which can be correlated to the fact that higher pH limits carbon availability from CO2, hence algal growth is suppressed 36, 37, 12. The biomass extracted from all variable pH ranges also showed highest biomass at control pH7.
This is directly proportional to algal growth. Decreased algal growth observed at alkaline pH is due to the fact that the mother cell, cell wall flexibility increases which in turn prevents its rupture and inhibits autospore release thus increasing the time for cell cycle completion 38, 12. In terms of days both growth and biomass had shown increasing trend from 0 to 21 day after which the declining trend was observed.
The lipid accumulation at pH 9 was highest and as the pH was decreased the lipid accumulation also showed decrease because alkaline pH indirectly results in increase in triglyceride accumulation 12, 38.
Exposing algae to lower or higher salinity levels than their natural levels can change growth rate and alter composition. In our experiments the growth rate and biomass decreased as the NaCl concentration in the growth medium increased and hence highest growth was observed in 0.0M culture and lowest was observed in culture grown in 0.25 M salinity. This could be associated with the fact that C.vulgaris was unable to adapt at higher saline ranges. Cultivation with different salinity ranges although showed similar time course i.e growth increased from 0 to 21day and declined on day 28. Higher lipid content was however observed in the medium with highest NaCl concentration ie at 0.25 M.
ACKNOWLEDGEMENT: The authors are grateful to Professor Aditya Shastri, Vice-chancellor, Banasthali University, Dr. Jerry Abraham, Senior Scientist and Dr. Dolly W Dhar, Principal Scientist, CCUBGA, Indian Agriculture Research Institute for providing necessary facilities.
1. Cardozo K.H.M; Guaratini T; Barros M.P; Falcão V.R; Tonon A.P; Lopes N.P; Campos S; Torres M.A; Souza A.O; P. Colepicolo; E. Pinto; Metabolites from algae with economical impact, Comp. Biochem. Physiol. C: Toxicol. Pharmacol. 2000; 146: 60–78.
2. Valencia I.; Ansorena, D; Astiasarán I. Development of dry fermented sausages rich in docosahexaenoic acid with oil from the microalgae Schizochytriumsp.:influence on nutritional properties, sensorial quality and oxidation stability,Food Chem. 2007; 104:1087–1096.
3. Converti, A.; Casazza, A.A.; Ortiz, E.Y.; Perego, P.; delBorghi, M. Effect of temperature and nitrogen concentration on the growth and lipid content of Nannochloropsisoculata and Chlorella vulgaris for biodiesel production.Chem. Eng. Process. 2009; 48, 1146–1151.
4. Spolaore, P.; Joannis-Cassan, C.; Duran, E.; Isambert, A. Commercial applications of microalgae. J. Biosci. Bioeng. 2006; 101, 87–96.
5. Illman AM, Scragg AH, ShalesSW: Increase in Chlorella strains calorific values when grown in low nitrogen medium. Enzyme MicrobTechnol. 2000; 27:631–635.
6. Liu Z.Y; Wang G.C; Zhou B.C. Effect of iron on growth and lipid accumulation in Chlorella vulgaris, Bioresour. Technol. 2008; 99:4717–4722.
7. Nigam, S; Rai, M.P. and Sharma, R. Effect of Nitrogen on Growth and Lipid Content of Chlorella pyrenoidosa; American Journal of Biochemistry and Biotechnology. 2011; 7 (3): 124-129.
8. Singh, J. and S. Gu;. Commercialization potential of microalgae for biofuels production. Renew. Sustainable Energy Rev., 2010; 14: 2596-2610.
9. Pruvost, J., G. Vooren, B. Gouic, A. Mossion and J. Legrand.Systematic investigation of biomass and lipid productivity by microalgae in photobioreactors for biodiesel application.Bioresource Technol. 2011; 102: 150-158.
10. Gao, C.; Zhai Y; Ding Y; Wu Q. Application of sweet sorghum for biodiesel production by heterotrophic microalga Chlorella protothecoides.Applied Energy. 2010; 87: 756-761.
11. Hu, Q. Environmental Effects on Cell Composition. In Handbook of Microalgal Culture: Biotechnology and Applied Phycology; Richmond, A., Ed.; Blackwell: Oxford, UK, 2004; pp 83–93.
12. Murthy G S, Ceballos R M and Juneja A, Effect of Environmental Factors and Nutrient Availability on the Biochemical Composition of Algae for Biofuels Production: A Review. Energies. 2013; 6, 4607-4638.
13. Thompson, G.A. Lipids and membrane function in green algae. Biochim.Biophys.Acta 1996, 1302, 17–45.
14. Shifrin, N.S.; Chisholm, S.W. Phytoplankton lipids: Interspecific differences and effects of nitrate, silicate and light-dark cycles. J. Phycol. 1981, 17, 374–384.
15. Wang, Z.T.; Ullrich, N.; Joo, S.; Waffenschmidt, S.; Goodenough, U. Algal lipid bodies: Stress induction, purification, and biochemical characterization in wild-type and starch less Chlamydomonasreinhardtii. Eukaryot. Cell 2009, 8, 1856–1868.
16. Demirbas, A. Use of algae as bio fuel sources. Energy Convers.Manag. 2010, 51, 2738–2749.
17. Takagi, M.; Watanabe, K.; Yamaberi, K.; Yoshida, T. Limited feeding of potassium nitrate for intracellular lipid and triglyceride accumulation of Nannochloris sp. UTEX LB1999. Appl. Microbiol. Biotechnol. 2000, 54, 112–117.
18. Stephenson, A.L.; Dennis, J.S.; Howe, C.J.; Scott, S.A.; Smith, A.G. Influence of nitrogen-limitation regime on the production by Chlorella vulgaris of lipids for biodiesel feedstocks. Biofuels 2010, 1, 47–58.
19. Goldberg, I.K., Cohen, Z., 2006. The effect of phosphate starvation on the lipid and fatty acid composition of the fresh water eustigmatophyte Monodussubterraneus. Phytochemistry 67, 696–701.
20. Rodolfi, L.,;Zittelli, G.C.; Bassi, N.; Padovani, G.; Biondi, N.; Bonini, G.; Tredici, M.R.; 2009. Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor. Biotechnology and Bioengineering 102 (1), 100–112.
21. Li Xin; Hu H, Gan K; Sun Y. Effects of different nitrogen and phosphorus concentrations on the growth, nutrient uptake, and lipid accumulation of a freshwater microalga Scenedesmus sp.; Bioresource Technology 2010; 101 5494–5500.
22. Kolber, Z.; Zehr, J.; Falkowski, P. Effects of growth irradiance and nitrogen limitation on photosynthetic energy conversion in photo system II. Plant Physiol. 1988, 88, 923–929.
23. Barsanti, L.; Gualtieri, P. Algae: Anatomy, Biochemistry, and Biotechnology, 1st ed.; CRC Press: Boca Raton, FL, USA, 2005.
24. Bligh, E.G and Dyer, W.J.A rapid method of total lipid extraction and purification. Can J BiochemPhysiol. 1959; 37:911-917.
25. Borchardt, J.A.; Azad, H.S. Biologicxtraction of nutrients. J. Water Pollut. Control Fed.1968, 40, 1739–1754.
26. Rai, L.C; Mallick, N; Singh, J.B and Kumar, H.D. Physiological and biochemical characteristics of copper tolerant and wild type strain of Anabaena doliolum under copper stress. J Plant Physiol. 1991;138:68-74.
27. Yanqun L, Horsman M, Wang B, Wu N and Lan C Q, Effects of nitrogen sources on cell growth and lipid accumulation of green alga Neochlorisoleoabundans. Applied Microbiology and Biotechnology. 2008; Volume 81, Issue 4, 629-636.
28. Fogg, G. Photosynthesis and formation of fats in a diatom. Ann. Bot. 1956, 20, 265–285.
29. Morris, I.; Glover, H.; Yentsch, C. Products of photosynthesis by marine phytoplankton: The effect of environmental factors on the relative rates of protein synthesis. Mar. Biol. 1974, 27, 1–9.
30. Kilham, S.; Kreeger, D.; Goulden, C.; Lynn, S. Effects of nutrient limitation on biochemical constituents of Ankistrodesmusfalcatus.Freshw. Biol. 1997, 38, 591–596.
31. Heraud, P.; FEMS Microbiology Letters 2005; 249: 219–225.
32. Mallick N; Mandal S; Singh A. K; Bishai M. and Dash A. Green microalga Chlorella vulgaris as a potential feedstock for biodiesel, 2011 Society of Chemical Industry, J ChemTechnolBiotechnol 2012; 87: 137–145.
33. Lee S.Y; Hong S H; Park S J; van W. R. and Middelberg APJ, Metabolic flux analysis on the production of poly (3-hydroxybutyrate), in Polyesters I: Biological Systems and biotechnological Production, ed by Doi Y and Steinbuchel A. Wiley-VCH Publishers, Weinheim, Germany,2001; pp. 249–261
34. Doi Y, Microbial Polyesters. VCH Publishers, New York, USA, 1990; p. 166.
35. Ohlrogge, J. and Browse, J. Lipid biosynthesis. Plant Cell 1995; 7:957–970.
36. Chen, C.Y.; Durbin, E.G. Effects of pH on the growth and carbon uptake of marine phytoplankton. Mar. Ecol.-Prog. Ser., 1994; 109, 83–94.
37. Azov, Y. Effect of pH on inorganic carbon uptake in algal cultures. Appl. Environ. Microbial. 1982 43, 1300–1306.
38. Guckert, J.B.; Cooksey, K.E. Triglyceride accumulation and fatty acid profile changes in Chlorella (Chlorophyta) during high pH induced cell cycle inhibition. J. Phycol., 1990; 26, 72–79
How to cite this article:
Kalla N and Khan S: Effect of nitrogen, phosphorus concentrations, pH and salinity ranges on growth, biomass and lipid accumulation of chlorella vulgaris. Int J Pharm Sci Res 2016; 7(1): 397-05.doi: 10.13040/IJPSR.0975-8232.7 (1).397-05.
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