Kitao Fujiwara

Size-dependent toxicity of silica nano-particles to Chlorella kessleri

SiO2 nano-particles were found to exhibit size-dependent toxicity toward the alga, Chlorella kessleri. Small SiO2 nano-particles exhibit stronger toxicity: 50% inhibitory concentrations (IC50) value for 5 nm = 0.8 ± 0.6%, 26 nm = 7.1 ± 2.8%, and 78 nm = 9.1 ± 4.7%. Enlargement of the cell body was observed by flow cytometry, which is due to the presence of structures that obstructed cell division. Optical and transmission microscopes were used to observe coagulated cells with incomplete division. Although the physiological effect of SiO2 nano-particles was not clear, SiO2 nano-particles are toxic, at least for algae in aquatic media. Under the transmission electron microscope, several amorphous structures appeared in the cells that were exposed to 5-nm silica nano-particles.

Thallium Induces Morphological Changes in the Photosynthetic Apparatus of Synechocystis sp. PCC6803

The aim of this study was to elucidate the mechanism of thallium (Tl) ion toxicity in photosynthetic organisms. The physiological and biochemical responses to Tl exposure were analyzed in the cyanobacterium Synechocystis sp. PCC6803, which is a widely used model to study photosynthesis. We examined the photosynthetic activities of Tl+-exposed cells, the extent of Tl accumulation, and the properties of membrane lipids. Exposure to Tl+ at 2.0 and 5.0 for 24 h decreased the net photosynthetic activities of cells to 92% and 34%, respectively. After exposure to 2.5 μM Tl+, cells concentrated the Tl to 20.8 μM on a packed cell volume basis. Exposure of Synechocystis to 0–2.5 μM Tl+ resulted in an approximately 9-fold concentration factor. Treatment with 2.0 μM Tl+ for 48 h decreased the total lipid content of the cells by 38%. Further, we observed the ultrastructure of cells treated with Tl+. The cells exposed to 5 μM Tl+ for 24 h showed thylakoid membrane fragmentation and generated less-dense particles following osmium staining. During this time, the net photosynthetic oxygen evolution of the cells was reduced to 34%. These results suggest that the accumulation of Tl in cells affects the integrity of the photosynthetic apparatus.

Effects of derivatization on solar-induced decomposition of polycyclic aromatic hydrocarbons in aqueous media

The solar-induced decomposition of 10 polycyclic aromatic hydrocarbons (PAHs) was observed in aqueous media. All 10 PAHs observed were half-decomposed within 120 min. Among anthracene derivatives, the decomposition rates were: anthracene = 1-methylanthracene < 2-methylanthracene < 9-methylanthracene < 9,10-dimethylanthracene ∼ 2-aminoanthracene. The addition of commercial humic acid had no effect on the decomposition rates of these PAHs. Deuterium water also hastened the decomposition of PAH. The products obtained by the solar radiation of PAH after extraction to DCM were mainly ketone and hydroxyl derivatives. To explaine these results, reactivities and electron charges at the constituent carbon atoms in each anthracene derivative were examined by an ab initio molecular orbital calculation method.

Protein cohesion induced by metal ions observed with fluorescence correlation spectroscopy

Nine metal ions were evaluated in the point of denaturating action of proteins. When some metal ions were added to the diluted protein solutions, aggregates appear: stronger denaturation causes the appearance of the larger-size aggregate. The size of the aggregatates are determined by fluorescence correlation spectroscopy (FCS). Green fluorescent protein (ZsGreen) and PE(phycoerythrin)-conjugated human-antibody monoclonal protein were employed as the target protein, of which solution was diluted 100–500 times and mixed with metal ions. According to this process, the denaturation power of metal ions is in the order of Mn2+≈ Fe2+< Co2+< Ni2+< Tl+< Cd2+< Cu+< Cu2+< Pb2+for ZsGreen, and Tl+≈ Ni2+< Cd2+< Fe2+< Cr3+≪ Pb2+for PE-conjugated antibody protein. Pb2+exhibits the strongest power of denaturation. In the case of ZsGreen, the denaturation power of metal ions is on the order of the Irving-Williams series, which provide the coordination tendency against ligands possessing nitrogen and oxygen. The present method with FCS is effective to evaluate the denaturation power of metal ions against proteins.