Promotion of biological H2 (Bio-H2) production by the nitrogen-fixing anaerobic microbial consortia using humin, a solid-phase humic substance

• Published in: Journal of bioscience and bioengineering 2022-08, Vol.134 (2), p.144-152
• Main Authors: Dey, Sujan, Kasai, Takuya, Katayama, Arata
• Format: Article
• Language: English
• Subjects: Bio-H2 production; Humin; Hydrogenase; Nitrogen-deficient condition; Nitrogen-fixing consortia; Nitrogenase
• ISSN: 1389-1723; 1347-4421
• DOI: 10.1016/j.jbiosc.2022.04.011

Dark fermentative biological hydrogen (Bio-H2) production is expected to be a clean and sustainable H2 production technology, and the technologies have been studied to increase in the product yield as index. This study achieved high product yields of Bio-H2 using nitrogen-fixing consortia under nitrogen-deficient conditions with glucose or mannitol as substrate and humin as the extracellular electron mediator: 4.12 mol-H2/mol-glucose and 3.12 mol-H2/mol-mannitol. The high Bio-H2 production was observed under the conditions where both nitrogenase and hydrogenase were active in the presence of humin. Nitrogenase activity was confirmed by acetylene reduction activity and hydrogenase activity by Bio-H2 production under nitrogenase-inhibiting conditions with NH4NO3. [Fe–Fe] hydrogenase detected by a specific PCR and acetate, butyrate, formate, lactate, and pyruvate produced as by-products suggested the involvement of both pyruvate-ferredoxin-oxidoreductase and pyruvate formate lyase pathways in Bio-H2 production. Humin promoted the Bio-H2 production beyond the capacity of the consortium, which had reached saturation with the optimum concentrations of glucose and mannitol. Carbon balance suggested the concurrent H2 consumption by hydrogenotrophic methanogenesis and acetogenesis. Bio-H2 production of the washed and starved consortium with reduced humin under conditions with or without NH4NO3 suggests that humin promoted hydrogenase and nitrogenase activity by donating extracellular electrons. Clostridium and Ruminococcus in the consortia were considered major hydrogen producers. Thus, this study demonstrated the outstanding potential of nitrogen-fixing consortia under nitrogen-deficient conditions with humin as an extracellular electron mediator for dark fermentative Bio-H2 production with high yields. •Promoting product yield of dark fermentative Bio-H2 by humin as extracellular electron mediator.•Higher Bio-H2 production under the nitrogen-deficient conditions where both hydrogenase and nitrogenase were active.•Activation of both nitrogenase and hydrogenase by humin as extracellular electron mediator.•Clostridium and Ruminococcus as dominant Bio-H2 producers.