Glyceric acid (GA), an unfamiliar biotechnological product, is currently produced as a small by-product of dihydroxyacetone production from glycerol by Gluconobacter oxydans. We developed a method for the efficient biotechnological production of GA as a target compound for new surplus glycerol applications in the biodiesel and oleochemical industries. We investigated the ability of 162 acetic acid bacterial strains to produce GA from glycerol and found that the patterns of productivity and enantiomeric GA compositions obtained from several strains differed significantly. The growth parameters of two different strain types, Gluconobacter frateurii NBRC103465 and Acetobacter tropicalis NBRC16470, were optimized using a jar fermentor. G. frateurii accumulated 136.5 g/liter of GA with a 72% D-GA enantiomeric excess (ee) in the culture broth, whereas A. tropicalis produced 101.8 g/liter of D-GA with a 99% ee. The 136.5 g/liter of glycerate in the culture broth was concentrated to 236.5 g/liter by desalting electrodialysis during the 140-min operating time, and then, from 50 ml of the concentrated solution, 9.35 g of GA calcium salt was obtained by crystallization. Gene disruption analysis using G. oxydans IFO12528 revealed that the membrane-bound alcohol dehydrogenase (mADH)-encoding gene (adhA) is required for GA production, and purified mADH from G. oxydans IFO12528 catalyzed the oxidation of glycerol. These results strongly suggest that mADH is involved in GA production by acetic acid bacteria. We propose that GA is potentially mass producible from glycerol feedstock by a biotechnological process.

The absorption coefficient of the dye used in dye-sensitized solar cells is a major factor in the total energy efficiency of the cell. In this work, we increased the absorption coefficient of the dye cis-(NCS) 2 bis(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II) used in such cells by having the dye adsorbed on silver islands. We studied the effect of the surface area of silver (per surface area of substrate) and the effect of dye concentration on this enhancement. This technique significantly enhanced the absorption coefficient of the Ru-dye for the metal-ligand charge-transfer transition, which generates electrons and holes in dye-sensitized solar cells. The enhancement ratio of the absorption was controlled by the amount of Ru-dye directly adsorbed on the silver islands. The absorption was enhanced by a factor of 149, which was achieved for a dye concentration of 3 × 10 -10 mol/cm 2 and an average surface area of silver island of 0.63 cm 2 /cm 2 of substrate. Such enhancement is expected to be useful in improving the electric energy conversion efficiency of dyesensitized solar cells.

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