| In the present study, the growth, total lipid content and fatty acid composition of 48 strains of marine diatoms, which were obtained from the Microalgae Culture Center (MACC), Ocean University of China, were examined firstly. Then several strains among them, which could grow well and rich in EPA were selected and their total lipid content and fatty acid composition were investigated under different culture conditions including salinity, light intensity, nitrogen concentration and harvest stage. The intraspecific variations in growth, total lipid content and fatty acid composition among 60 clones of Cylindrotheca fusiformis were also investigated in this study. Furthermore, the effect of UV radiation and growth phase on chlorophyll fluorescence and fatty acid composition of two diatoms, Phaeodactylum tricornutum and Chaetoceros muelleri, which were obtained from the CSIRO culture collection, Hobart, Australia, were studied. Finally, the relative proportions of the major macromolecules contained in the two diatoms and the changes with culture age were also determined rapidly, simultaneously, and inexpensively using Fourier Transform Infrared spectroscopy in this study.The primary results of this study were listed below. 1. Total lipid and fatty acid composition of 48 strains of marine diatomsChanges on growth, total lipid content and fatty acid composition of 48 strains of marine diatoms, which were obtained from the Microalgae Culture Center (MACC), Ocean University of China, were examined. The microalgae were grown under defined conditions and harvested during late exponential phase. The total lipid content (% of dry weight) of all the microalgal strains was 4.02-42.6%, with the highest proportion in B8 (42.6%), the lowest proportion in B204 (4.02%). The major fatty acids in all strains were 14:0 (1.0-24.9%), 16:0 (8.2-32.5%), 16:ln-7 (16.0-46.3%) and EPA (3.36-19.5%).The polyunsaturated fatty acids 16:2n-4, 16:3n-4, 16:4n-l and 20:4n-6 also comprised a significant proportion of the total fatty acids in some strains. The characteristic fatty acid composition of diatom is readily distinguishable from those of other classes of microalgae. Significant concentrations of the polyunsaturated fatty acid EPA were present in each of the diatom with the highest proportion in B222 (19.5%).2. Environmental factors regulation of growth and fatty acid composition in several selected strains of marine diatoms2.1 Effect of salinity on the growth and fatty acid composition of six strains of marine diatomsThe effect of salinity (18, 28 and 38) on the growth and fatty acid composition of six strains of marine diatoms Chaetoceros gracilis (B13), Cylindrotheca fusiformis (B211), Phaeodactylum tricornutwn (B114, B118 and B221) and Nitzschia closterium (B222) was investigated. The relative growth rate showed an increase in B13 and a decrease in B114 and B222 with the increase of salinity. The major fatty acids of the 6 strains were 16:0, 16:ln-7 and EPA. B211 also had high percentage of 20:4n-6 (5.6-7.4%). B13 also had high percentage of 14:0 (20.0- 30.9%). Saturated fatty acids decreased with the increase of salinity in B21K B221 and B222, and reached their highest values at salinity 18 in B211 (41.7%), B221 (37.6%) and B222 (31.7%), and at salinity 28 in B13 (48.1%), B114 (33.0%) and B118 (31.0%). Monounsaturated fatty acids increased inB114, B118, B221 and B222 while decreased in B13 and B211 with the increase of salinity. Polyunsaturated fatty acids had their highest values at salinity 18 in B13 (31.3%), B114 (19.6%), B118 (23.4%) and B222 (18.6%), and at salinity 28 in B211 (25.1%)andB221 (16.3%).2.2 Effect of light intensity on the total lipid and fatty acid composition of six strains of marine diatomsThe effect of light intensity (1500 Ix and 5000 Ix) on the total lipid and fatty acidcomposition of six strains of marine diatoms Cylindrotheca fusiformis (B211), Phaeodactylum tricornutum (B114, B118 and B221) Nitzschia closterium (B222) and Chaetoceros gracilis (B13) was investigated. The total lipids of B13,...
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