Enhanced hypoxanthine utilization for cAMP salvage synthesis efficiently by Arthrobacter sp. CCTCC 2013431 via xanthine oxidase inhibition

When hypoxanthine was utilized as the activator for the salvage pathway in cAMP synthesis, xanthine oxidase would generate in quantity leading to low hypoxanthine conversion ratios and cell viability. To enhance cAMP salvage synthesis, fermentations with citrate/luteolin and hypoxanthine coupling added were conducted in a 7 L bioreactor and then multiple physiological indicators of fermentation with luteolin addition were assayed. Due to hypoxanthine feeding, cAMP productivity reached 0.066 g/(L·h) with 43.5% higher than control, however, cAMP synthesis, cell growth and glucose uptake all ceased at 50 h which was shortened by 22 h in comparison to control. The addition of citrate resulted in the cessation of fermentation at 61 h, on the contrary, owing to luteolin addition, cAMP fermentation performance was enhanced significantly during the whole fermentation period (72 h) with higher hypoxanthine conversion ratios and cAMP contents when compared with citrate and only hypoxanthine added batches. Multiple physiological indicators revealed that luteolin inhibited xanthine oxidase activity reducing hypoxanthine decomposition and ROS generation. ATP/AMP, NADH/NAD⁺ and NADPH/NADP⁺ were significantly increased especially at the late phase. Moreover, HPRT, PUP expression contents and corresponding gene transcription levels were also elevated. Luteolin could inhibit xanthine oxidase activity and further decrease hypoxanthine decomposition and ROS generation leading to higher hypoxanthine conversion and less cell damage for cAMP salvage synthesis efficiently.