Isolation Of Autoinhibitor Produced By Isochrysis Galbana And Its Physiological Effects On Microalgae

During high cell-density culture of microalgae, some researcher found that the cells prevented each other, especially late during the incubation. The phenomenon also appeared in Isochrysis galbana. Besides the traditional factors, such as light, temperature, pH, aeration rate and nutrients, we suspect I. galbana produced autoinhibitor which effect the growth of itself and other biologic factors. We researched on the autoinhibitor and the main results obtained are listed as follow:1. The cell-free filtrate of I. galbana of 4 phases were tested for the effect on the growth of itself under the condition that light intensity, aeration rate, nutrition was not limited. Some autoinhibitor was produced and released gradually after the stationary phase, and the maximum was at the mortality phase. The autoinhibitor would also induce cell transformation from motile cells into non-motile cells.As the culture were older, the biochemical contents was declined, such as chlorophyll a, polysaccharides and proteins and the growth rate appeared subtractive.2. Allelopathy between I. galbana and Dunaliella salina, Platymonas spp., Phaeodactylum tricornutum, Chaetoceros gracilis, Chlorella pyrenoidosa, Nitzschia closterium was studied. It is suggested that cell density, proteins, polysaccharides and chlorophyll a and the phosphorus metabolism and nitrogen metabolism were affected by the old culture of I. galbana.3. The inhibitor was separated by extraction, gel-filtered on SephadexG-15 column, TLC. And the extract technicswas researched It is suggested that the inhibitor wasn't destroyed by heat and it was high polar. The optimum extraction technology was as follows: one-liter aliquots of the filtrates adjusted to pH2.4-3 were extracted three times with each 70ml of ethyl acetate. The exatracts were evaporated nearly dryness under reduced pressure at 40℃.4. The crude extraction was separated by gel-filtered on SephadexG-15 column, TLC.It was highly inhibited the growth of I. galbana.Its remention time is ranged 4.872±0.005min by reversed-phase high-performance liquid chromatography 5. The effects of nitrogen, phosphorus, renewal rate and renewal period on the cell productivity, cell total yield, DHA productivity and total yield of Isochrysis galbana were studied by the means of orthogonal design. The results showed that the cell productivity reached the maximum under the conditions of 11.5mg/L NO3--N concentration, 1.1mg/L PO43--P concentration, 0.20 renewal rate, 1 d renewal period, which was 0.3786g/L; and When the condition was 11.5mg/L NO3--N concentration, 0.7mg/L PO43--P concentration,0.20 renewal rate and 1d renewal period, DHA productivity was maximum, 7.707mg/(L·d)In brief, I. galbana released autoinhibitor into the culture medium, which as a new limiting factor feedback inhibited its cell growth.