| Two species of marine microalgae, Phaeodactylum tricornutum and Isochrysis galbana were cultured in batch under various conditions and their growth and polyunsaturated fatty acids (PUFAs) contents were investigated in order to optimize their PUFAs production.P. tricornutum grew best at 20℃ and its growth was significantly inhibited when temperature exceeded 25℃. /. galbana grew better at 25~30℃, but poorer below 15℃. EPA (eicosapentaenoic acid) and PUFAs contents based on dry mass were elevated by lowered temperature in P. tricornutum. Their contents increased by 90% and 50% at 10℃ compared with that at 25℃. DHA (docosahexaenoic acid) content in I. galbana showed the same tendency, but its PUFAs content reached the maximum at 20℃. The specific growth rate (μ) increased with increased light intensity and reached the maximal values of 0.86 d-1 in P. tricornutum, and 0.81 d-1 in /. galbana at 80μ mol m-2 s-1. EPA and PUFAs contents of P. tricornutum decreased as light intensity level was raised, however, those of /. galbana were raised by 110% and 16%, respectively, at 130 μ mol m-2 s-1 compared with that at 30 μ mol m-2 s-1, then decreased at light levels above 210μ mol m-2 s-1.Nitrogen sources and concentrations not only affected the growth but also PUFAs production of the two species of algae. At lower nitrogen concentrations (<1.80 mM), P. tricornutum showed better growth with NH4+, however, it grew faster with NH2CONH2 at higher concentrations (>3.50 mM). /. galbana grew fastest with NH2CONH2, but its growth was inhibited when NH/ concentration exceeded 0.90 mM. EPA content in P. tricornutum increased with increased nitrogen concentration within a range of 0.90 to 7.00 mM regardless of the nitrogen sources. Its PUFAs content decreased with NO3-, increased with NH2CONH2, but changed little with NH4+ as their levels were raised. DHA content in /. galbana showed the highest yield at 1.80 mM with NH4+ or NH2CONH2 and at 3.50 mM with NO3-. The biosynthesis of EPA and DHA was suppressed without nitrogen enrichment, resulting in the accumulation of C18:2(n-6) and C18:3(n-6)in P. tricornutum and C18:2(n-6) in /. galbana.The specific growth rate (μ) of P. tricornutum increased as the H2PO4 level was raised, but that of I, galbana decreased when the H2PO4- concentration was higher than 39 μM. In P. tricornutum, higher H2PO4- concentrations brought about lower EPA and PUFAs contents.tricornutum, higher H2PO4 concentrations brought about lower EPA and PUFAs contents. Although the highest EPA and PUFAs contents were obtained at 3 μM H2PO4-, the biomass yield was the lowest. DHA content in I. galbana increased with the increased H2PO4-concentrations and reached the maximum at 75 uM, however, its PUFAs content declined straightly.Fe3+ deficiency limited the algal growth. However, Fe + overdose (>24.5μM) was harmful to P. tricornutum, though it had little influence on /. galbana. Lower EPA and PUFAs contents of P. tricornutum were associated with higher Fe3+ levels. /. galbana showed the highest DHA and PUFAs contents at 60.5 uM Fe3+ and 24.5 uM Fe3+, respectively.CO2 enrichment in aeration enhanced the growth of the two algae With 2% CO2 (20000 ppmv), EPA and PUFAs contents of P. tricorntum increased respectively 1.3 and 1.9 times and that of DHA decreased by 29%, but PUFAs increased by 35% in /. galbana. It was found that elevation of CO2 concentration was an effective way for regulating PUFAs production.From the view point of PUFAs production, it was concluded that P. tricornutum cultured under the conditions of 15℃, 80 μmol m-2 s-1, 7.00 mM NH2CONH2, 75μM H2PO4-, 12.5 uM Fe3+ and enrichment CO2 could generate high EPA and PUFAs yields. High DHA and PUFAs outputs by /. galbana were obtained at 20℃, 130 μmol m-2 s-1, 1.80 mM NH2CONH2, 39 μM H2PO4- and 24.5 uM Fe3+ in CO2-enriched culture.
|
PDF Full Text Request