Two-stage enrichment of hydrogen-oxidizing bacteria as biofertilizers.

Biofertilizers can replace chemical fertilizers to promote the plant growth without causing any pollution. The study of hydrogen-oxidizing bacteria (HOB) enrichment as biofertilizers from mixed culture is scarce. Our recent study shows that biofertilizing HOB are successfully enriched in a short hydraulic retention time of 10 h. While, the mechanism is unknown. This study intentionally used a two-stage method to enrich biofertilizing HOB specifically with nitrate as nitrogen source in Stage 1 and then 1-aminocyclopropane-1-carboxylate (ACC) as nitrogen source in Stage 2. It was found Pseudomonas (34.46%, reported HOB) predominated in Stage 1, while Azospirillum (59.35%), Azoarcus (36%) were dominant genera and Azospirillum lipoferum strain DSM 1691 (50%), Azoarcus olearius strain DQS-4 (50%) were dominant species in Stage 2. The enriched HOB of Stage 2 showed ACC deaminase activity. Furthermore, they could also fix N 2 and consume Ca 3 (PO 4) 2. Thus, the two-stage method can be used as a specific enrichment for HOB as biofertilizers, which extends the application of HOB in agriculture. Image 1 • Two-stage method is feasible to enrich HOB as biofertilizers in mixed culture. • HOB predominate in Stage 1 with nitrate as nitrogen source. • HOB as biofertilizers dominate in Stage 2 with ACC as a selection pressure. • The ACC deaminase activity of enriched HOB is 58.4 nmol a-ketobutyrate/mg/h. • Enriched HOB have the ability of nitrogen fixation and phosphate solubilization. [ABSTRACT FROM AUTHOR]