Hypoosmoregulatory ability of eyed-stage embryos of chum salmon

To evaluate the osmoregulatory ability of eyedstage embryos of laboratory-reared chum salmon, Oncorhynchus keta, we examined changes in osmolality of the perivitelline fluid and blood following transfer to 50 and 100% seawater (SW), together with morphological changes in chloride cells present in the yolk sac membrane. Transfer to SW did not cause any significant change in the whole egg weight. However, the embryos shrank when the eggs were transferred to SW, whereas the perivitelline space increased at the expense of the embryo. Osmolality of the perivitelline fluid increased rapidly to reach environmental levels 3 h after transfer, indicating that the egg shell is permeable to ions and water. Blood osmolality increased after transfer to SW, reached a peak level at 3 h, and then decreased gradually. The chloride cells in the yolk sac membrane became activated following transfer, as shown by increased cell size and frequent appearance of apical openings. These results indicate that the eyed-stage embryos of chum salmon possess hypoosmoregulatory ability and that chloride cells in the yolk sac membrane may be involved in salt extrusion, in place of gill chloride cells, during the late embryonic stage.     

Degradation of dibromophenols by UV irradiation

We examined the degradation of dibromophenols （DBPs）, i.e. 2,4-DBP, 2,6-DBP and 3,5-DBP by ultraviolet （UV） irradiation and estimated the relationship between degradability and molecular orbital properties of each dibromopbenol. The removal of DBPs under a UV lamp system was successfully performed in an aqueous solution. After 5 min of irradiation, the initial DBPs concentration of 20 mg/L was decreased to below 1 mg/L, and about 60% of bromide ion was released. A decrease in the concentration of dissolved organic carbon （DOC） suggested the mineralization of DBPs, The mineralization may occur after release of bromide ions because the decrease of DOC was slower than the release of bromide ions. The degradability of 3,5-DBP was slightly lower than 2,6-DBP and 2,4-DBE Molecular orbital calculation suggested that the electrophilic frontier density and the highest occupied molecular orbital （HOMO） energy may be related to the degradability of DBPs.     

Genetic Engineering of Cyanobacteria to Enhance Biohydrogen Production from Sunlight and Water

To mitigate global warming caused by burning fossil fuels, a renewable energy source available in large quantity is urgently required. We are proposing large-scale photobiological H₂ production by mariculture-raised cyanobacteria where the microbes capture part of the huge amount of solar energy received on earth’s surface and use water as the source of electrons to reduce protons. The H₂ production system is based on photosynthetic and nitrogenase activities of cyanobacteria, using uptake hydrogenase mutants that can accumulate H₂ for extended periods even in the presence of evolved O₂. This review summarizes our efforts to improve the rate of photobiological H₂ production through genetic engineering. The challenges yet to be overcome to further increase the conversion efficiency of solar energy to H₂ also are discussed.