The corrosion of sewers and the control of odor are the major operational and maintenance problems in wastewater collection systems. The generation of hydrogen sulfide and subsequent sulfuric acid results from microbially mediated reactions, by sulfate-reducing bacteria (SBR) and sulfide-oxidizing bacteria. This review covers pertinent information about sulfate reduction-induced problems in general and SBR in particular. Metabolism with respect to carbon, energy, and sulfur sources, ecology, growth factors (dissolved oxygen, temperature, pH, and sulfide), and the competitive effects of methane-producing bacteria on SBR are discussed. Because metals react with sulfide to form metal sulfide precipitates with extremely low solubilities, metal interactions in sulfate reduction environments are discussed.
A Cr(VI)-reducing culture was enriched from an anaerobic chemos tat fed with synthetic media containing acetate and Cr(VI). The enriched culture was used for a series of batch tests to investigate several environmental factors affecting microbial Cr(VI) reduction. Under carbon-limiting conditions, the extent of Cr(VI) reduction proportionally depended on the carbon concentration and no reduction of Cr(VI) was observed in the absence of acetate. Cr(VI) reduction was also dependent upon the initial biomass level and the type of organic compounds. The developed model predicted Cr(VI) reduction well at different Cr(VJ) concentrations.Sulfate at 120 mg SO/-IL or nitrate at 150 mg NIL slightly inhibited Cr(VI) reduction. Reduction of nitrate but not sulfate was observed along with Cr(VI) reduction. Cr(VJ) was not reduced by the aerobically growing culture, and it was found that oxygen inhibitory effects on Cr(VI) reduction were reversible. The optimum pH and temperature for Cr(VI) reduction were found to be 7.3 and 32°C, respectively. In addition, Cr(VJ) reduction was sensitive to the metal ions that may coexist with Cr(VI) in industrial wastes containing Cr(VI). Water Environ. Res., 68, 1156Res., 68, (1996.
Normal cell cycle progression and proliferation of palatal mesenchymal cells are important for palatal development. As targets of miR-17-92, E2F transcription factors family has been suggested to induce the transcription of miR-17-92 in several cell types. In the present study, we sought to investigate whether this negative feedback loop exists in mouse PMCs and what the function of this negative feedback loop would be in palatal mesenchymal cells. Using GeneMANIA, we revealed that the most important function of experimentally verified targets of miR-17-92 is cell cycle regulation. E2F1 and E2F3, but not E2F2, were extensively expressed in mouse palate. Over-expression of E2F1 significantly increased the expression of all the members of miR-17-92. After increased by E2F1, miR-17 and miR-20a may negatively target E2F1, and thereby prevent the cells from excessive proliferation. We suggest that the negative feedback loop between E2F1 and miR-17-92 may contribute to palatal development by regulating the proliferation and cell cycle of palatal mesenchymal cells.
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