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ARS Home » Pacific West Area » Pendleton, Oregon » Columbia Plateau Conservation Research Center » Research » Publications at this Location » Publication #84132
Title: PHOTODISSIMILATION OF FRUCTOSE TO H2 AND CO2 BY A DINITROGEN-FIXING CYANOBACTERIUM ANABAENA VARIABLIIS

Author
item REDDY, P. - UNIVERSITY OF FLORIDA
item SPILLER, H - UNIVERSITY OF FLORIDA
item Albrecht, Stephan
item SHANMUGAM, K. - UNIVERSITY OF FLORIDA

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The ability of photosynthetic bacteria to produce hydrogen for fuel and chemical feedstocks was investigated. The results show that one type of photosynthetic bacteria can convert a simple sugar (fructose) to hydrogen and carbon dioxide. This conversion requires light. The individual cells of this bacteria occur in long chains or filaments and the production of hydrogen is located in specialized cells, called heterocysts, that are distributed throughout the filament. Using specific chemical inhibitors, it was found that an enzyme complex, or biocatalyst, called nitrogenase is responsible for the production of hydrogen. Hydrogen production by the bacteria increased in proportion to increasing concentrations of the sugar in the environment. But, the apparent conversion efficiency from sugar to hydrogen can be increased during shorter periods and optimum sugar concentrations. Additional measurements, under the same conditions, suggested that only 50% of the sugar was used to generate carbon dioxide. Under conditions when excess sugar is present, and hydrogen uptake by the bacteria is prevented, the elevated rate of hydrogen to carbon dioxide production indicated that water played a role in the sugar-mediated hydrogen production. Biochemical inhibition of hydrogen production indicated a role for photosynthesis in this process. The rate of hydrogen production by one strain of the bacteria was 46 ml per hour per g dry wt. This rate was maintained for over 15 days and about 30% of this hydrogen was derived from water. These results show that cyanobacteria can serve as biocatalysts in the high efficiency conversion of biomass-derived sugar to hydrogen, while simultaneously producing hydrogen from water.

Technical Abstract: The ability of cyanobacteria to serve as a biocatalysts in the production of hydrogen as a fuel and chemical feedstock was investigated. The results show that A. variabilis, when incubated under argon, dissimilated fructose to hydrogen and carbon dioxide in a light- dependent reaction. The hydrogen production had an obligate requirement for fructose is heterocyst dependent. Differential inhibition studies with carbon monoxide showed that nitrogenase is the main enzyme catalyzing the hydrogen production. Net hydrogen yield increased linearly with increasing concentrations of fructose up to 10 mM in the medium. The average apparent conversion efficiency of fructose to hydrogen was 10, although high conversion efficiencies of 15-17 can be obtained during shorter periods and optimum fructose concentrations. Under the same conditions, the ratio of carbon dioxide released to fructose removed was 3.0 suggesting that only 50% of the fructose carbon was oxidized to carbon dioxide. Under conditions of carbon excess, which prevents hydrogen uptake, the maximum ratio of hydrogen to carbon dioxide was found to be 3.0. This high value indicated that water was also a source of reductant in fructose-mediated hydrogen production. Inhibition of hydrogen evolution by DCMU demonstrated a role for photosystem II in this process. The rate of hydrogen production by A. variabilis strain SA1 was 46 ml per hour per g dry wt. This rate was maintained for over 15 days. About 30% of this hydrogen was derived from water. These results show that cyanobacteria can serve as biocatalysts in the high efficiency conversion of biomass-derived sugar to hydrogen, while simultaneously dissimulating water to hydrogen.