Exploring influence mechanism of small-molecule carbon source on heterotrophic nitrification-aerobic denitrification process from carbon metabolism, nitrogen metabolism and electron transport process

The heterotrophic nitrification-aerobic denitrification (HNAD) process can remove nitrogen and organic carbon under aerobic conditions. To get the in-depth mechanism of the HAND process, a strain named Acinetobacter johnsonii ZHL01 was isolated, and enzyme activity, electron transport, energy production, and gene expression of the strain were studied with small-molecule carbon sources, including sodium citrate, sodium acetate, sodium fumarate, and sodium succinate. The HNAD pathway of ZHL01 was NH₄⁺→NH₂OH → NO, and nitrogen balance analysis shows that ZHL01 could assimilate and denitrify 58.29 ± 1.05 % and 16.58 ± 1.07 % of nitrogen, respectively. The assimilation, the nitrification/denitrification, and the respiration processes were regulated by the concentration of reduced nicotinamide adenine dinucleotide (NADH) produced from the different metabolic pathways of small-molecule carbon sources. The HNAD process occurs to reduce intracellular redox levels related to NADH concentrations. This discovery provides a theoretical basis for the practical application of HAND bacteria.