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Isolation and characterization of microalgae with commercial potential

Indrayani, Indrayani (2017) Isolation and characterization of microalgae with commercial potential. PhD thesis, Murdoch University.

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This study focused on bioprospecting of microalgae species with commercial potential and their potential to be cultured under outdoor conditions, with the main focus on lipids/fatty acids and carotenoids. Species and strain selection was done by isolation of algal species from highly selective environments (hypersaline microalgae) and by selection of potential species from the Murdoch University culture collection. Three algae species have been isolated from hypersaline environments (the coccoid red, Amphora sp. MUR 258 and Navicula sp) and only one species, Botryococcus braunii 807/2, was from our culture collection. Through the initial selection processes, two promising species, Amphora sp. MUR 258 and Botryococcus braunii 807/2 were chosen for further study.

Amphora sp. MUR 258 is a newly isolated hypersaline pennate diatom (Bacillariophyceae) that contaminated and took over a Dunaliella salina culture grown in a 10m2 raceway pond at Murdoch University and showed promise as a lipid producer. Limits to growth factors, lipids and fatty acids profiles and the feasibility for outdoor long-term cultivation in open raceway ponds were studied. This strain was able to grow well over a wide range of temperatures (19-36oC) and salinities (6-12% NaCl). The optimum specific growth rates occurred at 25 and 35o C at 9 and 7% NaCl salinity, respectively. The cells accumulated more lipids in the exponential phase except, when cultured at the highest salinity (12% NaCl) when more lipids accumulated in the stationary phase. The highest lipid productivity (41.5 mg.L-1.d-1) was achieved at 9% salinity and 25oC. When grown under different N and P ratios, Amphora sp. MUR 258 achieved its highest biomass productivity (84.74 mg.L-1.d-1) at the lowest nutrient concentrations (1N:1P), whereas the highest lipid productivity (40 mg.L- 1.d-1) was observed at the highest nitrogen concentration (3N:1P). Cultures grown at high phosphorus concentration (1N:2P) had the lowest growth rate, biomass and lipid productivity. When grown under different N sources (sodium nitrate, ammonium nitrate, ammonium chloride or urea), Amphora sp. MUR 258 achieved its highest cell density (67X104 cells.mL-1), growth rate (0.33 d-1) and biomass productivity (74.1 mg.L-1.d-1) with urea. Irrespective of the growing conditions, the predominant fatty acids of the Amphora sp. MUR 258 were palmitic acid (C16:0), stearic acid (C18:0), palmitoleic acid (C16:1), and oleic acid (C18:1), as well as low quantities of eicosapentaenoic acid (C20:5). The fatty acid profile of this strain makes it a suitable species for biodiesel production.

Investigation on the reliability and performance of the long term growth of Amphora sp. MUR 258 in outdoor paddle-wheel driven raceway ponds in Perth, Western Australia showed that the alga can be grown successfully in semi-continuous culture outdoor raceway ponds for 13 months when culture salinity was kept between 8.6 and 14.9% NaCl. The highest cell density (167x104 cells.mL-1), specific growth rate (0.3 d-1), biomass (24 g.m-2.d-1) and lipid productivity (6.8 g.m-2.d-1) were achieved in summer. There was no contamination by other algae during the first three months of culturing, but after this some contamination by Navicula sp, Tetraselmis sp and Dunaliella sp were observed.

Botryococcus braunii strain 807/2 has been studied intensively in relation to its hydrocarbon production and its ability to grow outdoors in raceway ponds. However, B. braunii 807/2 also is a potential strain for carotenoid production. Carotenoid production of B. braunii 807/2 was studied under different growing conditions expected to favour carotenogenesis (nitrogen limitation, high iron concentration at low and high light). The rate of carotenoid production of B. braunii 807/2 was faster under nitrogen deprivation, high iron concentration at high light intensity than other growing conditions. Lutein was the predominant carotenoid (43-55% of total carotenoids) under optimum growing conditions (green cells), whereas canthaxanthin (6-13% of total carotenoids) and astaxanthin (3.2-28% of total carotenoids) were the major carotenoids of red cells grown indoors and outdoors, respectively.

In summary, this study suggests that the Amphora sp. MUR 258 and B. braunii 807/2 are promising strains for the production of lipids/fatty acids and carotenoids, respectively. However, further studies are still needed to optimize the growth and the production of the product of interest.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Borowitzka, Michael and Moheimani, Navid
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