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In contrast to most denitrifiers studied so far, Pseudomonas stutzeri TR2 produces low levels of nitrous oxide (N 2 O) even under aerobic conditions. We compared the denitrification activity of strain TR2 with those of various denitrifiers in an artificial medium that was derived from piggery wastewater. Strain TR2 exhibited strong denitrification activity and produced little N 2 O under all conditions tested. Its growth rate under denitrifying conditions was near comparable to that under aerobic conditions, showing a sharp contrast to the lower growth rates of other denitrifiers under denitrifying conditions. Strain TR2 was tolerant to toxic nitrite, even utilizing it as a good denitrification substrate. When both nitrite and N 2 O were present, strain TR2 reduced N 2 O in preference to nitrite as the denitrification substrate. This bacterial strain was readily able to adapt to denitrifying conditions by expressing the denitrification genes for cytochrome cd 1 nitrite reductase (NiR) (nirS) and nitrous oxide reductase (NoS) (nosZ). Interestingly, nosZ was constitutively expressed even under nondenitrifying, aerobic conditions, consistent with our finding that strain TR2 preferred N 2 O to nitrite. These properties of strain TR2 concerning denitrification are in sharp contrast to those of well-characterized denitrifiers. These results demonstrate that some bacterial species, such as strain TR2, have adopted a strategy for survival by preferring denitrification to oxygen respiration. The bacterium was also shown to contain the potential to reduce N 2 O emissions when applied to sewage disposal fields.Wastewater treatment processes produce one of the major greenhouse effect gases, nitrous oxide (N 2 O) (7,25,30). The global warming potential of N 2 O relative to that of carbon dioxide (CO 2 ) is 298 for a 100-year time horizon, and its concentration in the atmosphere continues to increase by about 0.26% per year (9). Nitrogen removal in wastewater treatment plants is essentially based on the activities of nitrifying and denitrifying microorganisms, both of which are inhabitants of activated sludge. Nitrifying bacteria aerobically oxidize ammonium to nitrite (NO 2 Ϫ ) and nitrate (NO 3 Ϫ ), which are then reduced anaerobically by denitrifying bacteria to gaseous nitrogen forms, such as N 2 O and dinitrogen (N 2 ). It has long been known that N 2 O can be produced during both nitrification and denitrification processes of wastewater treatment (3, 19, 23), but the cause of N 2 O emission during the nitrification process was not clear. We recently showed, however, using activated sludge grown under conditions that mimicked a piggery wastewater disposal, that N 2 O emission during the nitrification process depends on denitrification by ammonia-oxidizing bacteria (Nitrosomonas) (18). On the other hand, it is believed that denitrifying bacteria produce N 2 O as a byproduct when anaerobiosis is insufficient during the denitrification process, because N 2 O reductase is the enzyme that is most sensitive to oxygen (6). Pigg...

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Phytoestrogens, such as daidzein and genistein in plants are suspected as endocrine-disrupting chemicals (EDCs), because their chemical structures are similar to natural or synthetic estrogens, and have estrogenic activity in vitro and in vivo. An EDC study was carried out on the diets of various animals in vivo. However, many of these diets include phytoestrogens and may already possess estrogenic activity. In this study, we evaluated the estrogenic activity of phytoestrogens (such as daidzin, genistin, daidzein, genistein, coumestrol and equol) and the feed diets for experimental animals, such as fish, amphibians and reptiles, towards human estrogen receptors α (hER-α) and β (hER-β), and the genistein and daidzein content in these diets from HPLC analysis. Coumestrol showed the highest estrogenic activity for hER-α and-β in the-S9 test. Equol showed the highest estrogenic activity for hER-α in the +S9 test. The estrogenic activities of coumestrol, equol and genistein were approximately one hundred to two thousand times higher than that of daidzein. Many of these compounds showed higher compatibility with hER-β than with hER-α. A diet for fish from soybean was indicated to contain the highest amounts of genistein and daidzein. Moreover, this fish diet had the highest estrogenic activity for hER-α and-β. The estrogenic activity was found with hydrolysis by β-glucuronidase, showing higher compatibility with hER-β than with hER-α. In addition, correlation between the contents of genistein and estrogenic activities in the diets was found, with the exception of part of the diet. Therefore, this indicates that the genistein content contributes to the estrogenic activity of the diets. These results suggest that in vivo estrogenic activity might be caused by the diet provided to an experimental animal, indicating the necessity for more careful selection of the feeding diet and measurement of estrogenic substances when performing an in vivo screening assay for EDCs. Key words-endocrine-disrupting chemicals, estrogenic activity, yeast two-hybrid assay, phytoestrogen, feeding diet of enzymatic activity, disruption of the immune system, and carcinogenicity or genetic damage. 1) Various in vitro screening assays have been developed to evaluate EDCs that may bind to sex hormone receptors. Screening assays such as the receptor-binding assay check the direct binding ability of the chemical with the receptor and the use of cultured cells such as yeast cells to which the receptor gene is inserted are frequently used. As for in vivo assays, the immature rat uterotrophic assay 2) is used to determine estrogen and the hershberger assay 3) to determine androgens are mainly used for mammals, and plasma and/or hepatic vitellogenin induction assay to determine estrogenicity have been used in fish 4) and amphibians. 5) An EDC study was carried out on various ani

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Understanding of how operational parameters affect the composition of exoelectrogenic microbes is an important step in the development of efficient microbial fuel cells (MFCs). In the present study, single-chamber MFCs were inoculated with rice paddy-field soil and continuously supplied with an acetate medium containing different concentrations of NaCl (0–1.8 M). Polarization analyses showed that power output increased as the NaCl concentration increased to 0.1 M, while it was markedly diminished over 0.3 M. The increase in power output was associated with an increased abundance of anode microbes as assessed by protein assays. Notably, the power increase was also accompanied by an increase in the abundance ratio of Geobacter bacteria to total anode bacteria as assessed by pyrosequencing of 16S rRNA gene amplicons and specific quantitative PCR. Although most Geobacter species are known to exhibit high growth rates in freshwater media without NaCl, the present study shows that 0.1 M NaCl facilitates the growth of Geobacter in MFC anode biofilms. This result suggests that the optimum salt concentration in MFC is determined by the balance of two factors, namely, the solution conductivity and salt tolerance of exoelectrogens.