EFFECTS OF NITROGEN SOURCES AND CONCENTRATIONS ON THE GROWTH AND FATTY ACID COMPOSITION OF PHAEODA-CTYLUM TRICORNUTUM

In order to investigate the effects of nitrogen sources and the concentrations on fatty acid composition in microalgae,a marine diatom,Phaeodactylum tricornutum,was cultured in batch with varied nitrogen sources(NO 3-,NH 4+,NH 2CONH 2)and at different concentrations.Its growth and fatty acid composition were investigated.The results showed that P.tricornutum grew poorly in the cultures without addition of any nitrogen source,however,polyunsaturated fatty acids(PUFAs)and C 18 fatty acids(C 18∶0,C 18∶2(n-6),C 18∶3(n-6))accounted for higher percentages of total fatty acids compared to those with addition of the nitrogen sources.At low concentrations of the nitrogen sources(1.8mmol/L),the alga showed faster growth with NH 4+,and grew faster with NH 2CONH 2 at high concentrations (3.5mmol/L).With NH 4+ or NH 2CONH 2 as nitrogen sources,EPA(eicosapentaenoic acid)and PUFAs in percentages of the total fatty acids increased when nitrogen concentrations were raised from 0.9 to 7.0mmol/L.With NO 3-,the EPA and PUFAs percentages increased to the maximum at 1.8mmol/L NO 3-,then decreased with the increased NO- 3 levels,while the highest EPA Was 16.7% of the total fatty acids.EPA content on a dry mass base(w/w)increased with the increasing nitrogen concentrations within a range of 0.9 to 7.0mmol/L regardless of the nitrogen sources.At 7.0mmol/L NH 2CONH 2,the alga achieved the highest contents(2.6%EPA and 4.4%PUFAs of the dry weight,respectively).PUFAs content on dry mass decreased with increased.NO- 3,increased with enhanced NH 2CONH 2,but showed small variation with added NH 4+.