Effects Of Different Salt Concentrations On The Growth And Antioxidant Accumulation Of Five Spirulina Strains

Spirulina has been widely cultured because of its high nutrition contents. At present Spirulina is mainly cultured with fresh water, it consumes large amounts of fresh water resources. Additionally, contamination of heavy metals in surface water can decrease the quality of Spirulina. Using seawater to culture Spirulina can reduce the consume of fresh water and reduce the risk of polution, since Spirulina has a strong salt tolerance.In order to screen Spirulina strains which could be cultured in higher salt concentrations and explore the optical culture condition, in this study, we compared five strains of Sprulina cultured in different NaCl concentrations, and measured their antioxidant components in order to provide theoretical basises for Spirulina cultivation.Five Spirulina strains SP 843, SP 972, SP 438, SP 834, SP ZJ were used in the research. Five treatments control (Zarrouk medium without addition of NaCl),200,400, 600,800 mmol/L NaCl was added in Zarrouk medium, respectively. By measuring the growth curve, pigment contents, osmotic adjustment substances and the accumulation of antioxidants, we studied the effect of different salt concentrations on the growth and antioxidant accumulation of Spirulina.The results showed that in the lower salt concentrations the growth curve of five strains of Spirulina were accordance with the control, but 800 mmol/L NaCl inhibited the growth. Strains SP 843, SP 972 and SP 438 had higher salt tolerance and could growth well in 600 mmol/L NaCl. Scanning electron microscope observation showed no significantly change between experimental group and control group, they could cultured in sea water medium.Pigments in Spirulina were investigated in dfferent salt concentrations, phycocyanin increased in 200 and 400 mmol/L NaCl, but decreased over 600 NaCl, in 800 mmol/L NaCl, phycocyanin in SP 834 was only 33.62% of the control. The increase of salt concentration caused a decrease in chlorophyll a also. However, β-carotene was accumulated especially in high NaCl concentrations, β-carotene content of SP 843 was 2.24 times of the control in 600 mmol/L NaCl.Polysaccharide, proline, betaine are the main osmotic regulation substances in maintaining cell normal physiological activities, and they are also antioxidants. Our results showed these substances increased with the accumulation of salt concentrations. Both extracellular polysaccharide and intracellular polysaccharide were increased obviously in higher salt condition. In 600 mmol/L NaCl, extracellular polysaccharide in SP 843 and SP ZJ were 3.03,3.92 times of the control, respectively. In 800 mmol/L NaCl, SP 972, SP 438 had the highest intracellular polysaccharide, this two strains were 2.32,2.30 times of the control, respectively. Proline content slowly increased along with the salt concentrations. Betaine contents were the highest in 600 mmol/L NaCl among all NaCl concentrations, the contents of five strains were 2.65,2.59,2.38,2.49,3.24 times of the control, respectively. Unsaturated fatty acid is helpful in maintaining membrane fluidity, Spirulina accumulated more unsaturated fatty acids c18:1n9c、c20:3n6 at higher salt concentration.Salt stress may result in Spirulina cell membrane lipid peroxidation and cause MDA contents increased. In 800 mmol/L NaCl, the MDA contents of the five strains were 6.34, 6.08,4.04,5.26,2.63 times of the control, respectively. But the salt stress could induce higher antioxidant capacity of Spirulina, the antioxidant capacity of Spirulina make it able to induce stress mechanism and strengthen the antioxidant enzymes SOD, POD activity and hydroxyl radical scavenging capability. SOD and hydroxyl free radical scavenge activity in 800 mmol/L NaCl were the highest. POD were the highest in 600 mmol/L NaCl. T-AOC can reflect the total antioxidant capacity, in 600 mmol/L NaCl, the T-AOC contents of the five strains were 2.09,2.35,3.34,1.76,1.98 times of the control.This study was undertaken with the aim to explore the optical growth conditions of Spirulina and choose algae strains grown in seawater conditions. The result showed that three strains of five screened strains could cultured in seawater. The Spirulina cultured in seawater with about 600 mmol/L NaCl contained more antioxidants and had higher nutritional values.