Autotrophic, Heterotrophic, and Mixotrophic Nitrogen Assimilation for Single-Cell Protein Production by Two Hydrogen-Oxidizing Bacterial Strains

To recover a nitrogen resource from high-ammonia-nitrogen wastewater, two amphitrophic hydrogen-oxidizing bacteria (HOB), Paracoccus denitrificans Y5 and P. versutus D6, capable of nitrogen assimilation for single-cell protein (SCP) production were isolated. These two HOB strains could grow autotrophically with H-2 as an electron donor, O-2 as an electron acceptor, CO2 as a carbon source, and ammonia nitrogen (NH4+-N) as a nitrogen source. The cell molecular formulas of strains Y5 and D6 determined by autotrophic cultivation were C3.33H6.83O2.58N0.77 and C2.87H5.34O3.17N0.57, respectively. The isolated strains could synchronously remove NH4+-N and organic carbon and produce SCP via heterotrophic cultivation. The rates of removal of NH4+-N and soluble chemical oxygen demand reached 35.47 and 49.04%, respectively, for Y5 under mixotrophic cultivation conditions with biogas slurry as a substrate. SCP content of strains Y5 and D6 was 67.34-73.73% based on cell dry weight. Compared with soybean meal, the SCP of Y5 contained a variety of amino acids.