Lipid Biomarkers Of Marine Algae During Decomposition In Natural Seawaters

Two marine algae were cultured and harvested at early exponential growth phase and late stationary phase. The compositions and concentrations of algal lipids(neutral lipids and fatty acids) during decomposition in naturl oxic seawater were examined. Also via this study, the distributions and contents of membrane and intracellular fatty acids of algae from late stationary stage were investigated. The main findings were as follows:1. The lipid compositions of microalgae at different growth stage during decomposition in naturl oxic seawaterNeutral lipids were composed of phytol, four kinds of alcohols (12-ROH , 14-ROH , 16-ROH, 18-ROH) and sterols of microalgae at early exponential growth phase and late stationary phase. But the sterols were different between two marine algae. The sterols of Platymonas subcordiforus contained 27â–³⁵ (27â–³⁵,Cholest-5-En-3β-ol),27â–³⁰ (27â–³⁰,5α-cholest-22-en-3β-ol),28â–³^5,22 (28â–³^5,22, 24-methylcholest-5, 22- Dien-3β-ol), 28â–³²² (28â–³²², 24-methylcholest-22- en-3β-ol), 28â–³⁵ (28â–³⁵, 24-methylcholest-5- en-3β-ol), 28â–³⁰ (28â–³⁰, 23, 24-dimethyl-5α-cholest-22-en-3β-ol), 29â–³^5,22 (29â–³^5,22, 24-Ethylcholestt-5, 22-Dien-3β-ol),29â–³²² (29â–³²², 23, 24-dimethyl-5α-cholest-22-en-3β-ol),29â–³⁵ (29â–³⁵, 24-Ethylcholestt-5-en-3β-ol), 29â–³⁰ (29â–³⁰, 23, 24-dimethyl-5α-cholest-22-en-3β-ol), 30â–³²² (4α, 23, 24-trimethyl-5α-cholest-22-en-3β-ol). Isochrysis galbana included ten kinds of sterols except 27â–³⁰ . However, fatty acid composition varied due to harvest time. The algae at exponential stage included seven saturated (12:0, 14:0, 15:0, 16:0, 17:0, 18:0, 20:0), three monounsaturated (18:1(n-9), 18:1(n-7), 20:1), and two polyunsaturated (18:2, 20:5) fatty acids. In addition to the same fatty acids as before, 16:1(n-9) and 22:6 were included in Platymonas subcordiforus harvested at late stationary stage, and Isochrysis galbana 3011 also contained 16:1(n-9), 16:1(n-7) and 22:6. 2. The lipid compositions and concentrations of two marine algae harvested at early exponential growth phase during decomposition in naturl oxic seawaterTotal fatty acids concentration of Platymonas subcordiforus changed little during aerobic incubation in the first month , one month after the concentration increased apparently. After significant decrease in the first week, total fatty acids concentration of Isochrysis galbana 3011 enhanced. Compwered with the fatty acids, the contents of algal neutral lipids were less. Total concentration of algal neutral lipids reduced obviously in the first month during the incubation, and one month after the concentration increased slightly.16:0 ( 50% of total fatty acids) and 18:0 (²0% of total fatty acids) were the dominating saturated fatty acids of two microalgae, but the components varied with algal species. For Platymonas subcordiforus, the concentration of the 16:0 fatty acid increased rapidly from the thirtieth day although the concentration decresed slightly in the first month. The 18:0 fatty acid have exhibited an increasing trend during the incubation with a faster rate in the second half month. The concentration of 16:0 and 18:0 fatty acids reduced in the first half month for Isochrysis galbana 3011, and 16:0 decreased more rapidly. After decreasing the concentrations of two compounds showed a accumulation. The major unsaturated fatty acid 18:1(n-9) in Platymonas subcordiforus degraded with time ,and the concentration dropped to zero at the end of the incubation. But 18:1(n-9) and 18:2 in Isochrysis galbana 3011 changed with complicated patterns.Neutral lipids included alcohols, phytol and sterols. Among them phytol and sterols were major components. Phytol of two microalgae showed a dramatic decomposition degradation and were completely degraded after fifty days. Several sterols were found in two microalgae and they changed with diversities of patterns.3. The lipid compositions and concentrations of two marine algae harvested at late stationary phase during decomposition in naturl oxic seawaterThe initial concentrations of total fatty acids in microalgae harvested at late stationary phase were higher than that of early exponential growth phase and the degradation patterns were different. The concentration of total fatty acids of Platymonas subcordiforus increased slightly within the former 14 days, but during the 14th day to 21th day the concentration decreased rapidly, then followed by a slight increase in concentration. Apparently distinct with Platymonas subcordiforus, total fatty acids of Isochrysis galbana 3011 degraded remarkably but in the last week of incubation the concentration raised gently. The total neutral lipids contents of two algae were less than their total fatty acids contents of each. For Platymonas subcordiforus, total neutral lipids concentration decreased rapidly within three days, after which little change in concentration. The total neutral lipids of Isochrysis galbana 3011 degraded in the first month, one month after the concentration was almost unchanged.The concentrations of 16:0 and 18:0 were higher than the other fatty acids in Platymonas subcordiforus. In the first two weeks of incubation 16:0 changed little but 18:0 increased rapidly in concentration, two weeks after both of them degraded clearly. 14:0, 16:0 and 18:0 were the dominating saturated fatty acids of Isochrysis galbana 3011, but they showed different degradation patterns. In the first month of incubation the concentration of 14:0 fatty acid reduced rapidly, after one month the concentration remained constant. 16:0 fatty acid degraded witnin 35 days followed by a little fluctuation in concentration. 18:0 fatty acid has exhibited a complex mode. 18:1(n-9) is the most abundant unsaturated fatty acid of Platymonas subcordiforus and it degraded in the first three weeks then followed by a significant enhancement in concentration. For Isochrysis galbana 3011, 18:1(n-9) fatty acid showed no obvious change after the first week although it degraded rapidly at the beginning of the incubation.The initial concentrations of phytol in microalgae harvested at late stationary phase were higher than that of early exponential growth phase, and they degraded significantly with time, respectively. 28â–³⁵, the major sterol of Platymonas subcordiforus presented rapid degradation and its concentration almost dropped to zero until the 14th day. But after the first two weeks 28â–³⁵ exhibited an obvious increasing. Isochrysis galbana 3011 was abuntant in 29â–³^5,22,29â–³⁵,30â–³²². The concentrations of 29â–³^5,22 and 29â–³⁵ remained almost constant in the first two weeks, while both compounds degraded after two weeks with 29â–³⁵ decreasing faster. 30â–³²² showed an increasing in concentration in the first week , then followed by slow degradation.4. The distributions and contents of membrane and intracellular fatty acids of two algae harvested at late stationary stageFor Platymonas subcordiforus, the components and contents of membrane and intracellular fatty acids were apparently distinct in the aerobic degradation of the different periods of incubation. At the beginning, the contents of membrane and intracellular fatty acids were 14.03% and 85.97%, respectively. The main intracellular fatty acids were 16:0 (39.08%), 18:1(n-9) (18.41%) and 18:0 (10.87%). In the 7th day, fatty acids in membrane and intracellular components showed different distributions. The membrane fatty acid content is extremely low (3.7%), while the contents of intracellular 16:0 (49.46%) and 18:0 (28.32%) were close to 90%.In the first, the contents of membrane and intracellular fatty acids in Isochrysis galbana 3011 were 79.30% and 20.70% respectively. The major fatty acids in membrane were 18:1 (n-7) (5.97%) and 18 : 0 (5.73%), while 16:0 (26.19%), 14:0 (13.04%) and 16:1(n-9) (11.09%) were the dominating intracellular components. The fatty acid composition was contrast to initial distribution in the 42th day with more membrane content (75.61%) and less intracellular fatty acids (24.39%). The main membrane fatty acids were 16:0 (36.03%) and 18:0 (30.22%), but 16:0 (8.77%) and 14:0 (4.16%) were the major intracellular components.