초록
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 H<SUB>2</SUB> backpressure by continuous H<SUB>2</SUB> removal (''milking'') can significantly increase the yield of H<SUB>2</SUB> in this strain. We show that ''milking'' by continuous selective consumption of H<SUB>2</SUB> using an electrochemical cell produces the maximum increase in H<SUB>2</SUB> yield (11-fold) and H<SUB>2</SUB> rate (3.4-fold), which is considerably larger than through ''milking'' by non-selective dilution of the biomass in media (increases H<SUB>2</SUB> 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 7-8days and extracts 39% of the energy content in glycogen as H<SUB>2</SUB>. Non-selective dilution stimulates H<SUB>2</SUB> production by shifting intracellular equilibria competing for NADH from excreted products and terminal electron sinks into H<SUB>2</SUB> production. Adding a mixture of the carbon fermentative products shifts the equilibria towards reactants, resulting in increased intracellular NADH and an increased H<SUB>2</SUB> yield (1.4-fold). H<SUB>2</SUB> 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.