Comparison Of Nutrients Between Nostoc Flagelliforme? Synechocystiss And Chlorella, And Rubisco Gene Expression Under Salt Stress

As an important food-type nitrogen fixing cyanobacteria, Nostoc flagelliforme also known as "facai", mainly distributed in country-semi-arid regions. Nostoc flagelliforme has an extremely high nutritional value and is rich in amino acids, carbohydrates, protein and Ca, Mg, K, Na, etc. Besides, extracellular polysaccharide (EPS) separated from Nostoc flagelliforme is also an active substance that has great potential for natural medicine development. However, because of the slow pace of natural reproduction and irrational exploitation. Nostoc flagelliforme is on the verge of extinction now. This high demand and low supply of Nostoc flagelliforme and its EPS is the main challenge and roadblock of its commercialization. So how to improve the growth efficiency of Nostoc flagelliforme is a major concern. It has been found that the yield and activity of Nostoc flagelliforme EPS was higher under salt-stressed culture than normal conditions.Based on this findings, in this paper, we compared main nutrients among Nostoc flagelliforme, Synechocystiss and Chlorella. And then isolated and purified their EPS, compared the basic physicochemical property and oxygen radicals scavenging capacities. Finally, Rubisco activity and gene expression were investigated in algae under normal and salt-stressed culture (0.3M). The results will provide theoretical basis and new ways for amplification culture of Nostoc flagelliforme and increase Nostoc flagelliforme EPS reproduction rates. The primary results are as follows:(1) Under normal culture, both growth rate and chlorophyll content of Nostoc flagelliforme were lower than Synechocystiss and Chlorella. EAA content in protains of Nostoc flagelliforme, Synechocystiss and Chlorella were all in accordance with ideal protein pattern recommended by FAO/WHO. They are also rich in favor amino acids, which are accounted for 43.96%,45.06% and 49.72% of the TAA, respectively. Unsaturated fatty acids of Nostoc flagelliforme, Synechocystiss and Chlorella were up to 50%, of which the polyunsaturated fatty acids content is between 41.73%?51.79%. All three algae have high content of essential fatty acids. About 17.15% of acid linoleic was detected in Nostoc flagelliforme. Linolenic acid was detected in Synechocystiss and Chlorella were 16.58% and 28.07%, respectively. Linoleic acid was detected in Synechocystiss and Chlorella were 20.67% and 16.49%, respectively. So the three algae have similar nutritive composition, and all of them were good sources for high-quality protein, DHA and EPA.(2) EPS from Nostoc flagelliforme, Synechocystiss and Chlorella were precipitated and purified (expressed as EPSF, EPSJ and EPSX). EPSF, EPSJ and EPSX were all relatively homogeneous polysaccharide which contained uronic acid. All EPS were contained ?-glucosidic bonds, EPSJ and EPSX were also contained a-glucoside bonds.The highest EPS yield was EPSJ (422.39 mg/g, dw) which was 4.10 times of EPSJ and 1.84 times of EPSX. The average molecular weight of EPSF, EPSJ and EPSX were 2.5 kDa,705.5 kDa and 105.1 kDa, respectively. The polydispersity index were 1.03,1.76 and 7.50, which shows that EPSF was the low-molecular weight polysaccharide, EPSF and EPSX were the high-molecular weight polysaccharide. The highest ability of EPS to scavenge oxygen free radicals was EPSF (78.96 ?mol·Trolox g-1), followed by EPSJ (44.29 ?mol·Trolox g-1) and the EPSX was the lowest (24.65 ?mol·Trolox g-1).(3) Synechocystiss can adapted to the salt stress within 0-0.7 mol/L NaCl, Chlorella can adapted to the salt stress within 0-0.3 mol/L NaCl. And the growth rate under salt-stressed culture was lower than that of normal cultue both of Synechocystiss and Chlorella. Under salt-stressed culture, the cell of Nostoc flagelliforme appeared yellow, and the chain structure gradually disintegrated and dispersed into single vegetative cell. The cell of Synechocystiss and Chlorella didn't show any significant changes in cell morphology, and the cumulative number of dividing cells decreased.(4) Under normal and salt stressed culture, the growth rate and Rubisco activity of Nostoc flagelliforme were lower than Synechocystiss and Chlorella.Rubisco gene expression of Nostoc flagelliforme was stable within 0.35, but still lower than Synechocystiss and Chlorella. Under salt stressed culture (0.3 mol/L), Rubisco gene expression of Nostoc flagelliforme was stable within 0.48, but Rubisco gene expression changed greatly in Chlorella and was low in Synechocystiss (0.34). However, considering the Rubisco gene expression, growth rate and Rubisco activity, Synechocystiss has higher RuBPcase activity than Nostoc flagelliforme, and it can maintained rapid growth even under salt-stressed culture.