The Characteristics Of Growth And Arachidonic Acid Production In The Microalgae Parietchloris Incisa And Myrmecia Incisa

The freshwater green microalga Parietochloris incisa comb. nov (Chlorophyta, Trebouxiophyceae) was found to be the richest plant source of the long-chain polyunsaturated fatty acids (PUFAs), arachidonic acid (AA). When P. incisa is cultivated under nitrate starvation, the fatty acid content constituted over 35% of dry weight, the proportion of AA exceeded 60% of total fatty acids and 21% of dry weight. AA is accumulated mainly in TAG deposited in cytoplasmic oil bodies in which over 90% of total AA is deposited in triacylglycerols, makes this species a potential candidate for commercial production of AA. Myrmecia incisa is also belong to Chlorophyta, Trebouxiophyceae which is much more similar to the P.incisa in morphology.The M. incisa is of special interest in whether it can accumulate more AA.We investigated the effects of the nitrate, phosphate, light intensity and the light-path of glass photobioreactors on the growth, total lipids (TL) and AA content in P. incisa and M. incisa. The main results were summarized as follows:1. Both microalga can grow well under four different nitrate concentrations when cultivated with BG-1 lmedium and the nitrate concentrations had no obvious influence on their final dry weight. The TL reached maximum to 33.37% of dry weight, and the proportion of AA comprising 36.63% of total fatty acids (TFA) and 11.56% of dry weight (DW) in P. incisa under low nitrate concentration. While the TL and AA of the M. incisa achieved 26.97% (TFA) and 9.04%(DW) under low nitrate concentration. Both microalga can harveste the maximum TL and AA under low nitrate concentration, and the P. incisa can accumulate much more AA.2. The phosphate concentration had significantly reduced the growth of two microalga and the final biomass were different. The TL in both microalga had no difference when the phosphate concentrations increased from 8 to 20 mg-L"1, the P. incisa yielded 28%(TFA) and the M. incisa achieved 20%(TFA). Low phosphate concentration was propitious to the accumulation of TL3. When the two microalga exposed to the 130μmol-m-2·s-1 and 260μmol-m-2·s-1, the latter resulted in an enhancement of both the growth and TL content. The TL of P. incisa accounted for 39.36%(DW) when the light intensity was 260μmol-m-2·s-1, which was much higher than 33.37% under 130μmol-m-2·s-1. The TL of M. incisa obtained 32.47%(DW) under 260μmol·m-2·s-1, while cultivated under the 130μmol-m-2·s-1 the TL only account for 26.96%.4. In all experiments, both the microalga had a growth reduction under low nitrate concentration in glass photobioreactors with a light path length of either 3 cm or 6 cm. But M. incisa can accumulate much more TL when the light-path length of glass reactors was 3 cm.