Nitrate reduction by Paracoccus thiophilus strain LSL 251 under aerobic condition: Performance and intracellular central carbon flux pathways

The intracellular carbon metabolic flux pathways of denitrifying bacteria under aerobic conditions remain unclear. Here, a newly strain LSL251 was identified as Paracoccus thiophilus. Strain LSL251 removed 94.79% and 98.78% of total organic carbon and nitrate. 74.66% of nitrogen in culture system was lost as gaseous nitrogen. Moreover, C-13 stable isotopic labeling and metabolic flux analyses revealed that the primary intracellular carbon metabolic pathways were the Entner-Doudoroff pathway and the tricarboxylic acid (TCA) cycle. Electrons are primarily donated as direct electron donor-NADH through the TCA cycle. Furthermore, response surface methodology modeled that the highest total nitrogen removal efficiency was 98.43%, where the optimal parameters were C/N ratio of 8.00, 32.98 degrees C, 50.18 rpm, and initial pH of 7.73. All together, these results have shed new lights on intracellular central carbon metabolic distribution and flux pathways of aerobic denitrifying bacteria.