Ieaki Uemura

Fermentative metabolism to produce hydrogen gas and organic compounds in a cyanobacterium, Spirulina platensis

The non nitrogen-fixing and filamentous cyanobacterium Spirulina platensis NIES-46 produced hydrogen gas, ethanol, and low molecular organic acids auto-fermentatively under dark and anaerobic conditions. The fermentative productivity was enhanced by incubating the cyanobacterium under nitrogen-starved conditions. Cell-free extracts of the cyanobacterium catalyzed hydrogen production by the addition of acetyl-coenzyme A and pyruvate. Pyruvate-degrading and acetaldehyde dehydrogenase activities were observed in the cell-free extracts. These results suggest that the fermentation was dependent on the anaerobic degradation of endogenous glycogen via pyruvate.

Heterologous expression of clostridial hydrogenase in the Cyanobacterium synechococcus PCC7942.

The Clostridium pasteurianum hydrogenase I has been expressed in the cyanobacterium Synechococcus PCC7942. The Shine-Dalgarno sequence of the structural gene encoding hydrogenase I from C. pasteurianum was changed to that of the cat (chloramphenicol acetyltransferase) gene. The hydrogenase gene was cloned downstream of a strong promoter, isolated from Synechococcus PCC7942, with the cat gene as a reporter gene. Expression of clostridial hydrogenase was confirmed by Western and Northern blot analyses in Synechococcus and Escherichia coli, whereas in vivo/in vitro measurements and activity staining of soluble proteins separated on non-denaturing polyacrylamide gels revealed functional expression of hydrogenase only in cyanobacterial cells. The changed Shine-Dalgarno sequence appeared to be essential for the functional expression of clostridial hydrogenase in Synechococcus, but had no influence on the expression and activity of clostridial hydrogenase expressed in E. coli.

Effect of culture temperature shift on the cellular sugar accumulation of Chlorella vulgaris SO-26

Abstract We investigated the effect of culture temperature on the maximum specific growth rate and cellular sugar accumulation, and the effect of a temperature shift on the sugar accumulation of cells of an Antarctic green alga, Chlorella vulgaris SO-26, in a batch culture system. Decreases in temperature appeared to correlate with decreases in the maximum specific growth rate; on the other hand, the cellular sugar content showed a reverse tendency against temperature. We attempted to use this tendency to improve sugar productivity in Chlorella. First, we cultured Chlorella at 20°C during the logarithmic growth phase to obtain a high specific growth rate. The culture temperature was then shifted from 20°C to 14°C during the stationary growth phase to increase the cellular sugar content. As a result, we obtained a 25% increase in sugar production over that obtained by culture at 20°C throughout the culture.

Hydrogenase-Mediated Hydrogen Metabolism in A Non-Nitrogen-Fixing Cyanobacterium, Microcystis aeruginosa

Hydrogen metabolism in a non-nitrogen-fixing cyanobacterium, Microcystis aeruginosa, was studied. The cyanobacterium evolved hydrogen gas under dark and anaerobic conditions. The rate of hydrogen evolution was higher in cells grown under nitrogen-limited conditions than under nitrogen-sufficient conditions. Hydrogen uptake occurred immediately when light was irradiated to the hydrogen-evolving cells in darkness. The light-dependent uptake of hydrogen was not sensitive to the inhibitor for photosystem II, DCMU [3-(3,4-dichloro-phenyl)-1,1-dimethyl urea], but sensitive to the antagonist of plastoquinone, DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone). These results suggest that hydrogen may be produced with degradation of endogenous storage materials, such as glycogen, and be taken up by the light-dependent reaction of photosystem I via plastoquinone.

Preparation of a Langmuir–Blodgett film of a platinized viologen-linked porphyrin and photoinduced hydrogen evolution

A Langmuir–Blodgett film of a platinized viologen-linked porphyrin is prepared, and steady photoinduced hydrogen evolution is observed with the porphyrin under steady-state irradiation.

Photosynthetic Bacterial Hydrogen Production with Fermentation Products of Cyanobacterium Spirulina platensis

The cyanobacterium Spirulina platensis accumulates glycogen photoautotrophically in a nitrogen-deficient medium. Under anaerobic conditions in the dark, the glycogen degrades into organic compounds. As molecular hydrogen also evolves in this process, hydrogenase participation is suggested in this metabolism. We investigated the several conditions necessary for the evolution of hydrogen and production of organic compounds. The effects of cell concentration, initial pH, and concentration of the buffer were determined.