Enrichment of hydrogen-oxidizing bacteria with nitrate recovery as biofertilizers in the mixed culture

Hydrogen-oxidizing bacteria (HOB) can utilize hydrogen and oxygen to produce valuable products in biomass, including polyhydroxyalkanoates, microbial proteins, and biofertilizers. However, the method of enriching HOB as biofertilizers from mixed culture remains unknown. In this study HOB were enriched with nitrate as nitrogen source at a hydraulic retention time of 10 h. The nitrate consumption rate was 120 mgN/L/d or 16 mg N/g VSS/h, which was comparable to those of denitrification using organic carbon or hydrogen. The percentage of Azospirillum (dominated genus, reported biofertilizing HOB) was 84.89% and the dominated species was Azospirillum lipoferum strain DSM 1691. Furthermore, the enriched HOB had the abilities of 1-aminocyclopro-pane-1-carboxylate conversion and phosphate solubilization, the functions of biofertilizers. This is the first re-port on the enrichment of biofertilizing HOB from mixed culture. Meanwhile, the enriched HOB can recover nitrate from wastewater without any secondary nitrogen pollution, extending HOB application for resource recovery from wastewater.