Studies On The Physicochemical Characteristics And Biological Activity Of Polysaccharides In Nostoc Sphaeroides Colony At Different Growth Stages

Nostoc sphaeroides Kützing is an edible cyanobacterium traditionally used as food and medicine.Despite successful large-scale culture of N.sphaeroides colonies,changes of bioactive substances(including polysaccharides)during colony growth are still unknown.Here we divided the colony growth into four different stages,i.e.1-2mm,2-3mm,3-4mm and 4-5mm stages,according to colony size,and investigated bioactive polysaccharides from differet growth stages and also polysaccharide hydrolyzates of final colony products.(1)Nostoc sphaeroides colonies at different growth stages.It took 65 days from alal filaments to the 1-2mm stage,15 days from the 1-2mm stage to the 2-3mm stage,15 days from the 2-3mm stage to the 3-4mm stage and15 days from the 3-4mm stage to the 4-5mm stage.As the colonies grew,their color changed from light green to dark green and agal density decreased,while protien and sugar contents were almost unchanged.(2)Physicochemical characteristics of polysaccharides from Nostoc sphaeroides colonies at different growth stages.The polysaccharide yield was～28% at the 1-2mm,2-3mm and 3-4mm stages,but it was decreased to ～8%at the 4-5mm stage.The infrared spectra of polysaccharides from different stages are similar,while their molecular weight distribution had similar elution peaks but with different area ratio.The monosaccharide components of the polysaccharides from different colony growth stages were similar,mainly including xylose,mannose,galactose and glucose with a molar ratio is 1∶1∶1∶2,while trace amount of glucuronic acid was also found in the polysaccharides.(3)Antioxidant activity of polysaccharides from Nostoc sphaeroides colonies at different growth stages.Using ABTS and DPPH free radical scavenging experiments,all the polysaccharides from different stages were found to have in vitro antioxidant activity.Oxidative survival experiments using Caenorhabditis elegans models also demonstrate that all the polysaccharides were able to increase the survival rate of the nematodes under oxidative stress.(4)Preparation and physicochemical characteristics of Nostoc sphaeroides oligosaccharides.Partial hydrolysis of the polysaccharide was performed using weak hydrochloric acid and trifluoroacetic acid,respectively,which was confirmed by gel filtration chromatography profiling.The infrared absorption spectra of the oligosaccharides prepared by both acid hydrolysis methods were similar to those of the parent polysaccharides.The monosaccharides contained in the oligosaccharides were similar with the polysaccharides but with different molar ratio.(5)Bioactivity of Nostoc sphaeroides oligosaccharide preparations.Oxidative survival and lifespan experiments using wild-type C.elegans demonstrate that the oligosaccharide preparations were able to increase survival rate under oxidative stress conditions and extend lifespan under normal conditions.Chemo-avoidance experiment using a Huntington’s disease-like C.elegans model further showed that the oligosaccharide preparations were able to improve the avoidance behavior of the nematode.In conclusion,physicochemical characteristics and antioxidant activity of the polysaccharides from different N.sphaeroides colony growth stages were similar but with a decreased polysaccharide yield.Oligosaccharide preparations were found to have similar infrared absorption spectra and similar monosaccharides but at different molar ratio.The oligosaccharide preparations were found to have antioxidant and anti-aging effects like their parent polysaccharide but also have neuroprotective potential,unlike the polysaccharides.