title: Enhancing biological hydrogen production from cyanobacteria by removal of excreted products.
abstract: Hydrogen is produced by a [NiFe]-hydrogenase in the cyanobacterium Arthrospira (Spirulina) maxima during autofermentation of photosynthetically accumulated glycogen under dark anaerobic conditions. Herein we show that elimination of H₂ backpressure by continuous H₂ removal ("milking") can significantly increase the yield of H₂ in this strain. We show that "milking" by continuous selective consumption of H₂ using an electrochemical cell produces the maximum increase in H₂ yield (11-fold) and H₂ rate (3.4-fold), which is considerably larger than through "milking" by non-selective dilution of the biomass in media (increases H₂ yield 3.7-fold and rate 3.1-fold). Exhaustive autofermentation under electrochemical milking conditions consumes >98% of glycogen and 27.6% of biomass over 7-8 days and extracts 39% of the energy content in glycogen as H₂. Non-selective dilution stimulates H₂ production by shifting intracellular equilibria competing for NADH from excreted products and terminal electron sinks into H₂ production. Adding a mixture of the carbon fermentative products shifts the equilibria towards reactants, resulting in increased intracellular NADH and an increased H₂ yield (1.4-fold). H₂ production is sustained for a period of time up to 7days, after which the PSII activity of the cells decreases by 80-90%, but can be restored by regeneration under photoautotrophic growth.
authors.affiliation: Waksman Institute of Microbiology and Department of Chemistry & Chemical Biology, Rutgers University, Piscataway, NJ 08854, USA.
authors.forename: Gennady M
authors.initials: GM
authors.lastname: Ananyev
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Skizim
authors.forename: G Charles
authors.initials: GC
authors.lastname: Dismukes
mesh_terms: D056804:Biofuels; D018533:Biomass; D019149:Bioreactors; D001709:Biotechnology / Q000379:methods*; D002264:Carboxylic Acids / Q000378:metabolism; D002470:Cell Survival; D055664:Electrochemical Techniques; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D006859:Hydrogen / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006864:Hydrogenase / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010788:Photosynthesis; D053545:Spirulina / Q000737:chemistry / Q000378:metabolism*
chemical_list: D056804:Biofuels; D002264:Carboxylic Acids; D009243:NAD; D000431:Ethanol; D009249:NADP; D006859:Hydrogen; C043296:nickel-iron hydrogenase; D006864:Hydrogenase