title: Optimization of metabolic capacity and flux through environmental cues to maximize hydrogen production by the cyanobacterium "Arthrospira (Spirulina) maxima".
abstract: Environmental and nutritional conditions that optimize the yield of hydrogen (H(2)) from water using a two-step photosynthesis/fermentation (P/F) process are reported for the hypercarbonate-requiring cyanobacterium "Arthrospira maxima." Our observations lead to four main conclusions broadly applicable to fermentative H(2) production by bacteria: (i) anaerobic H(2) production in the dark from whole cells catalyzed by a bidirectional [NiFe] hydrogenase is demonstrated to occur in two temporal phases involving two distinct metabolic processes that are linked to prior light-dependent production of NADPH (photosynthetic) and dark/anaerobic production of NADH (fermentative), respectively; (ii) H(2) evolution from these reductants represents a major pathway for energy production (ATP) during fermentation by regenerating NAD(+) essential for glycolysis of glycogen and catabolism of other substrates; (iii) nitrate removal during fermentative H(2) evolution is shown to produce an immediate and large stimulation of H(2), as nitrate is a competing substrate for consumption of NAD(P)H, which is distinct from its slower effect of stimulating glycogen accumulation; (iv) environmental and nutritional conditions that increase anaerobic ATP production, prior glycogen accumulation (in the light), and the intracellular reduction potential (NADH/NAD(+) ratio) are shown to be the key variables for elevating H(2) evolution. Optimization of these conditions and culture age increases the H(2) yield from a single P/F cycle using concentrated cells to 36 ml of H(2)/g (dry weight) and a maximum 18% H(2) in the headspace. H(2) yield was found to be limited by the hydrogenase-mediated H(2) uptake reaction.
authors.affiliation: Department of Chemistry, Princeton University, Hoyt Laboratory, Princeton, NJ 08544, USA.
authors.forename: Gennady
authors.initials: G
authors.lastname: Ananyev
authors.forename: Damian
authors.initials: D
authors.lastname: Carrieri
authors.forename: G Charles
authors.initials: GC
authors.lastname: Dismukes
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000693:Anaerobiosis; D018533:Biomass; D000458:Cyanobacteria / Q000378:metabolism*; D003624:Darkness; D005285:Fermentation; D006003:Glycogen / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000378:metabolism; D007700:Kinetics; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism
chemical_list: D009566:Nitrates; D009243:NAD; D009249:NADP; D006859:Hydrogen; D000255:Adenosine Triphosphate; D006003:Glycogen; C043296:nickel-iron hydrogenase; D006864:Hydrogenase