Physiological Mechanism for Enhanced Cyclic Adenosine Monophosphate Biosynthesis by Sodium Nitrate in Arthrobacter sp. CCTCC M2013431

Objectives: The aim of this study is to elucidate the physiological mechanism for enhanced cyclic adenosine monophosphate biosynthesis by nitrate in Arthrobacter sp. CCTCC M2013431. Methods: Firstly,optimal sodium nitrate adding condition was determined by fermentations conducted in shaking flask and cAMP fermentation with optimal condition was carried out in a 7 L fermentation tank. Then,fermentation kinetic parameters,nitrate utilization,reducing force level,key enzymes activities,intracellular amino acids levels and energy metabolism were analyzed. Results: Due to the addition of 3 g/L-broth sodium nitrate into fermentation broth at 24 h,cAMP concentration and yield on glucose achieved 5.02 g/L and 0.097 g/g,with the improvements of 22.7% and 29.8%,respectively,when compared with those of control. Activities of glucose-6-phosphate dehydrogenase were improved greatly by lower NADPH levels caused by plentiful consumption during nitrate reduction process,meanwhile,the metabolic intensity of glycolysis pathway was weakened while activities of key enzymes in pentose phosphate pathway and tricarboxylic acid cycle were significantly increased. More carbon flux was directed into pentose phosphate pathway and purine synthesis pathway for cAMP production. In addition,intracellular precursor amino acids levels,NADH/NAD⁺ and ATP/AMP ratios were also enhanced greatly by nitrate which supply sufficient energy for cAMP synthesis. Conclusion: Nitrate utilization consumed redundant reducing force which changed the distribution of metabolic flux among different pathways,and improved intracellular amino acids levels and ATP synthesis,then cAMP fermentation synthesis was promoted greatly. The physiological mechanism of nitrate for enhanced cAMP biosynthesis provided reference materials for nucleotide fermentation production.