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Title: The effect of environmental conditions on the fatty acid composition of microalgae and cyanobacteria
Author: Hopley, Antoinette
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1993
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A range of freshwater algae (Chlorelia vulgaris 211/8K, Chlorella vulgaris 211/11c, Ankistrodesmus antarcticus 202/25, Scenedesmus obliquus 276/3A, Cvanidium caldarium 1355/4), marine and brackish algae (Nannochloris atomus 251/4B, Nannochloropsis oculata 849/1, Isochrvsis galbana 927/1, Isochrysis sp. 927/14) and cyanobacteria (Anabaena flos-aquae 1403/13A, Anabaena variabilis 1403/12, Synechococcus sp. 1479/5, Synechococcus sp. PCC 7943) were grown in batch culture at initial nitrogen levels of 5, 25, 50 and 500 mg NO3-N I-1 or NH4-N I-1 (C. caldarium only) at three growth temperatures. Cultures were harvested in exponential and stationary growth phases. Protein, carbohydrate, lipid and fatty acid contents were determined. All the algae and cyanobacteria investigated exhibited changes in cellular content of protein, carbohydrate and lipid in relation to changes in temperature, nitrogen availability and growth phase. C. vulgaris 211/8K, C. vulgaris 211/11c, N. atomus, and the cyanobacteria all exhibited a major shift to carbohydrate accumulation at stationary phase and with decrease in growth temperature, with the exception of the cyanobacteria which did not exhibit a uniform response to temperature. Ank. antarcticus and S. obliquus exhibited major shifts to lipid accumulation with decrease in temperature and at stationary growth phase. Protein contents of the cyanobacteria increased at stationary phase in contrast to the decrease at stationary phase observed in the freshwater, marine and brackish algae. Carbohydrate, protein and lipid contents were all found to depend on previous nitrate availability in the cultures. The marine and brackish species showed a much broader range of fatty acids (C12 - C22) than the freshwater algae (predominantly C16 and C18) and cyanobacteria (predominantly C14, C16, C18). Quantitative changes in individual fatty acids rather than qualitative changes were found with temperature changes and growth phase. The degree of unsaturation decreased with decrease in temperature in the marine and brackish species in contrast to the increase in unsaturation observed with the freshwater algae and cyanobacteria. Based on the results of the laboratory work, six algae and cyanobacteria - C. vulgaris 211/8K, S. Obliquus, N. atomus, Isochrysis sp., A. flos-aquae, Synechococcus sp. PCC 7943 - were grown outdoors in a slurry based minipond system. All the species chosen grew successfully in algal treated slurry, with preferential uptake of ammonium-N before nitrite-N and nitrate-N. The algae behaved similarly outdoors in defined media and algal treated slurry to the laboratory based growth in relation to cellular content changes. Manipulation of specific cell constituents in a slurry based system would improve the economics of algal wastewater treatment, the resultant biomass having economic potential. The interest in algal fatty acid content manipulation would probably only be in the aquaculture field, and not from medical or health food areas due to health hazards associated with sewage. Carbohydrate accumulating algae would also be of interest to the aquaculture field. The current high cost of production of algal feeds has spurred the search for alternative algae production, and it is suggested that growth in slurry with nitrogen depletion to optimise lipid, carbohydrate or specific component fatty acid production maybe an alternative.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available