Preparation,Structure Characterization And Biological Activities Of An Extracellular Polysaccharide From Rhodopseudomonas Palustris

Rhodopseudomonas palustris is one of the representative strains of photosynthetic bacteria.It is usually applied in agriculture fishery environmental protection,medicine and other fields.Rhodopseudomonas palustris is riched in various biological active proteins,polysaccharides,pantothenic acid,carotenoids and vitamin B.So it is widely used as a probiotic in aquaculture.On one hand,it acts as a feed additive and improves feed efficiency,on the other hand it can inhibit harmful bacteria,maintain normal bacteria and improve local immunity and disease resistance.In this paper,we mainly studied the extraction,purification,physicochemical properties,sugar chain structure and immunomodulatory activity of extracellular polysaccharides from Rhodopseudomonas palustris,in order to provide a theoretical basis for the comprehensive utilization of Rhodopseudomonas palustris and the molecular basis of its probiotics properties.The main results are mentioned as follows:?1?The homopolysaccharide component RPS-30 was isolated and purified by fractional alcohol precipitation from the fermentation of Rhodopseudomonas palustris.The molecular weight was 46.82 kDa,which was determined by high performance gel permeation chromatography.?2?Analysis of monosaccharide composition by high performance liquid chromatography showed that RPS-30 was a homopolysaccharide,with total carbohydrate content of 94.13%and protein content of 1.32%,composed by mannose.Endotoxin test results show that there were no detectable levels of endotoxin in the fraction?<0.1 EU/mL?.?3?Fourier Transform Infrared Reflectance Spectroscopy?FT-IR?analysis showed that RPS-30 has characteristic absorption peaks of polysaccharides in the range of 3300cm^-12935cm^-1 1404cm^-1 1318cm^-1 1246cm^-1 and 1200-1000cm^-1.Scanning electron microscopy?SEM?images showed that RPS-30 had irregular layered structures with a mass of spherical particle aggregation.?4?Analysis of methylation and nuclear magnetic resonance?NMR?analysis showed that RPS-30 had a skeleton consisted by 1?2 and 1?4 linked?-mannose residues and the side chain was connected by 1?6 and 1?2,6 linked?-mannose residues.?5?We also studied the immunomodulatory activity of RPS-30 on the basis of macrophage RAW264.7 cell line.Through the detections of phagocytic activity,NO release,the mRNA expression levels of nitric oxide synthase?iNOS?,pro-inflammatory factors TNF-?,IL-6,IL-1?and anti-inflammatory factor IL-10,the mRNA expression levels suggested that RPS-30 could not only activate macrophages by stimulating the expression of pro-inflammatory cytokines but also could avoid the potential adverse effects caused by excessive activation of macrophages by promoting the expression of anti-inflammatory cytokines.?6?We found that RPS-30 has growth promoting effects on three common intestinal probiotics Lactobacillus reuteri Bacteroides thetaiotaomicron and Akkermansia muciniphila by in vitro anaerobic culture and determination of growth curves.