Construction And Biological Characteristics Of Polysaccharide Bacteria System

Glycogen accumulating organism(GAOs)have received extensive attention in nitrogen and phosphorus removal,treatment of low C/N ratio waste-water,and synthesis of intracellular storage polyhydroxyalkanoates(PHA).Moreover,the intracellular storage mechanisms and metabolic pathways of GAOs have acquired some understanding.However,the enrichment culture of GAOs and the growth pattern in sewage biological treatment systems are still unclear.The biological metabolisms of GAOs involved in key functional genes and complete glycogen metabolical pathways also remain elusive.Therefore,a comprehensive functional analysis of the stable GAOs system will not only further improve the intracellular storage mechanisms and energy generation for GAOs,but also give full knowledge to regulate the biological wastewater treatment process through the metabolic performance of GAOs.In this study,we used sodium acetate as the substrate to construct a sequencing batch reactor(SBR)with an anaerobic-aerobic cycle operation.A special method with drainage after anaerobic was adopted to restrict the phosphorus accumulating bacteria(PAOs)proliferation during the aerobic period and promote the enrichment growth of GAOs effectively.The results on the carbon source conversion of the activated sludge demonstrated that the operating strategy successfully constructed the GAOs enrichment system,and the reactor showed typical GAOs characteristics after39 d.The results showed that glycogen was degraded and PHA was synthesized during the anaerobic period,PHA was consumed and glycogen was synthesized during the aerobic period,and phosphate was almost not released or absorbed.System microorganisms were mainly cocci and Brevibacteria.Fluorescence in situ hybridization(FISH)further confirmed that two types of common GAOs,Candidatus contendobacter(Ca.contendobacter)and Candidatus Competibacter phosphatis(Ca.competibacter)existed in the GAOs enrichment system.Metagenomic analysis of the bacteria community showed that the GAOs were mainly composed of three typical GAOs including Ca.contendobacter,Ca.Competibacter phosphatis and Candidatus Propionivibrio aalborgensis(Ca.P.aalborgensis).Ca.contendobacter was the dominant GAOs in this study,and its relative abundance was as high as 7.01%,and finally stabilized between 2.72% and 3.22%.The metatranscriptomic analysis of typical anaerobic-aerobic cycle showed that the EMP pathway was the most important pathway of glucose metabolism,and the ED pathway and the pentose phosphate pathway were almost not expressed.According to KEGG analysis,we found that the ethyl-malonyl-Co A pathway(EMC)was a potential pathway for PHV synthesis,which was different from the pathways of PHV metabolism in the previous studies.We further found that the glyoxylate cycle was highly expressed to provide energy for system metabolism during the anaerobic period in the GAOs system,and aerobic environment promoted the expression of the TCA cycle.By introducing the concept of expression coefficient and establishing screening criteria,key differentially expressed genes(DEGs),such as mhd,sdh A,pck A,glg P,phb C and ccr,etc.(P<0.05),were screened out,among which the expression of mdh and ace A could be used as key genes to analyze the expression of glyoxylate cycle in the GAOs system.In addition,the expression of key genes confirms the potential role of EMC and other pathways.This study not only completely uncovered the intracellular storage mechanism and the characteristics energy metabolism for GAOs,but also laid a theoretical foundation for regulating the process of pollution removal and the wide application of GAOs in the waste water treatment process.