Characteristics And Regulation Of Carbon And Nitrogen Metabolism In Aphanizomenon Flos-aquae

Cyanobacteria,a phylum of bacteria that obtain their energy through photosynthesis,is a main contributor of the global primary producer.As the main nutritional and metabolic models in cyanobacteria are similar to photosynthetic eukaryote and higher plants,cyanobacteria is a good metabolism research model for biology study.In this work,Aphanizomenonflos-aquae 943 was chosen as research material.Aphanizomenon flos-aquae is a filamentous cyanobacterium capable of both photosynthesis and dinitrogen fixation under aerobic conditions.A series of physiological,biochemical and metabolic indicators were studied.Characteristics and regulation rules of carbon metabolism and other nitrogen assimilation pathway were investigated in the whole cell level.The optimum condition for the growth of Aphanizomenonflos-aquae was studied in BG11 medium by examining effects of temperature,initial pH value,nitrogen sources and air flow during the cultivation.Results showed that fittest circumstances for Aphanizomenon flos-aquae growth was:temperature of 21-22℃,the initial pH value of 6.37,0.41/min air flow.Improved nitrogen(NO₃^--N)or carbon(CO₂)resources promoted the growth of algae cells only under the balance of inorganic carbon and nitrogen elements.Under the experimental conditions,the algal cells can not use ammonium nitrogen in the medium directly,and heterocyst of Aphanizomenon flos-aquae cells cultured in BG11 with ammonium can not be observed.It means that ammonium ion can inhibit the growth of Aphanizomenon flos-aquae completely.In order to study the effect of inorganic carbon on heterocyst development,air with different CO₂ concentrations was bubbled to the medium.Comparing with air,CO₂ markedly improved the growth rate of Aphanizomenon flos-aquae and heterocyst differentiation,and heterocyst differentiation frequency in a certain time related to CO₂ concentration. However,the addition of NaHCO₃ did not induce the production of heterocysts.The increased CO₂ concentration in the medium caused the imbalance between carbon and nitrogen elements,which enhanced heterocyst frequencies rather than increasing the absorpion of cells to nitrogen source.It means the algae cells nitrogen metabolism existence of a multi-level multi-channel metabolic regulation.Nitrate reductase and glucose-6-phosphate dehydrogenase activity were calculated respectively.Nitrate reductase activity decreased by the addition of CO₂.The determination of 2-ketoglutarate showed that the accumulation of 2 - ketoglutaric acid was corresponding increased to the number of heterocyst cells.The effects of different inorganic carbon on other species of micro-agle were studied.Phaeodactylum tricornutum and Chlorella cultured at 1%and 3%CO₂ content achieve the highest growth rate respectively.Total hydrocarbon,total protein and carbon nitrogen ratio were calculated,the hydrocarbon accumulated in the cell was increased as well as the C/N ratio compared with the access to the concentration of CO₂,due to increased CO₂ concentration promoted photosynthetic activities.