Metabolic characterization ofAcetobacter diazotrophicus

Abstract

Carbon and nitrogen metabolism were investigated in Acetobacter diazotrophicus Pal 3, a N2-fixing bacterium able to grow at low pH and at high sugar concentration. Enzymatic, respiratory, and uptake studies were performed. The main active pathway for the catabolism of phosphorylated glucose was the pentose phosphate pathway. In addition, A. diazotrophicus directly oxidized glucose, gluconate, and ketogluconates through respiratory chain-linked enzymes. Soluble enzymes for the oxidation of glucose and gluconate were also found. Acetobacter diazotrophicus had a complete tricarboxylic acid cycle with a respiratory chain-linked malate dehydrogenase. The ability to grow on two- and three-carbon substrates would be explained by the presence of gluconeogenesis. Lack of bacterial growth on dicarboxylates was explained by the absence of a transport system. Ammonium assimilation proceeded mainly through glutamate dehydrogenase under ammonium excess but also through energy-demanding glutamine synthetase and glutamate synthase under N2-fixing conditions. Acetobacter diazotrophicus was not able to transport sucrose and its ability to grow on this disaccharide was explained by the presence of an extracellular enzyme with saccharolytic activity.Key words: Acetobacter diazotrophicus, carbon–nitrogen metabolism, extracellular saccharolytic activity, sucrose–succinate uptake.