Simultaneous oxygen and nitrate respiration for nitrogen removal driven by aeration: Carbon/nitrogen metabolism and metagenome-based microbial ecology

The overall goal of this research was to clarify the metabolic relationship between the nitrate removal and aerobic respiration driven by oxygen intrusion in mixed consortia of bacteria using metagenomic analysis. Aerobic respiration could stimulate nitrate transformation by facilitating nitrate uptake and nicotinamide adenine dinucleotide (NADH) generation and transportation, while creating an optimal niche for denitrification. A stoichiometric analysis of electron transformation verified that more electrons were consumed during biomass synthesis and less during aerobic denitrification with increasing aeration intensity (AI). We newly found that the amount of intracellular poly-beta-hydroxybutyrate (PHB) and NADH peaked in the moderate aeration reactor [R2, 0.25 L/(L center dot min)], which produced the highest total nitrogen (TN) removal rate [1.45 mg/(L center dot min)] ever reported. Thauera phenylacetica (31.91 % in R1) and Azoarcus sp. Strain BH72 (10.37 % in R2, 10.45 % in R3, and 16.83 % in R4) were the primary denitrifiers in the non-aerated (R1) and aerated reactors (R2, 0.25; R3, 0.63; and R4, 1.25 L/(L center dot min)), respectively. In particular, Thauera. phenylacetica, as a generalist, could conduct complete carbon and nitrogen metabolism in comparison with Azoarcus sp. Strain BH72. An analysis of the microbial metabolic characteristics and potential co-occurrence network indicated that intermediate exchanges, substrate competition, and effective respiration protection among the keystone taxa would be a vital underlay for efficient carbon metabolism and nitrogen transformation. This study sheds light on the metabolic mechanisms of aerobic denitrification in mixed bacterial consortia and offers theoretical guidance for optimizing existing aeration-based techniques.

Automated summary

The aim of this research was to investigate the metabolic relationship between nitrate removal and aerobic respiration in mixed bacterial consortia. The study found that aerobic respiration can stimulate nitrate transformation by facilitating nitrate uptake and generating NADH. It was also discovered that the highest total nitrogen removal rate was achieved in a reactor with moderate aeration intensity, where the intracellular levels of poly-beta-hydroxybutyrate (PHB) and NADH were highest.