Biology of anaerobic bacteria

Sulfate reducing bacteria of the genus DESULFOVIBRIO and homoacetogenic bacteria of the genus SPOROMUSA were sensitive to changes of hydrogen concentrations during the growth on an organic substrate. Increase of hydrogen concentrations competitively inhibited the organic substrate degradation and decrease of hydrogen concentration inhibited the respiration and the reduction of the external electron acceptor. Such hydrogen sensitive strains which seem to intermediarily produce and consume hydrogen ("hydrogen-cycling") were cultivated in the presence of a second hydrogen oxidizer. Both organisms competed for the hydrogen excreted by the first strain. The competence for H2-oxidation of the strains depended not only on hydrogenase affinities but also on the free energy change of H2-oxidation differing with the respective electron acceptors. (Résumé d'auteur

From overhead projection to effective interactive learning software for science students

Small, simple, highly interactive software modules have been developed to help science students surmount some of the main barriers for effective learning (as experienced in traditional lecture-based teaching): lack of motivation, lack of rapid and specific feedback, lack of interaction with the learning material, and lack of the opportunity to apply newly acquired knowledge. These modules are different to other multimedia materials currently available in that: · they will allow students to progressively test their assumptions and further their understanding of scientific concepts. Students will develop not only conceptual understanding but also problem-solving skills; · the use of academics as software developers means that the modules can be easily changed in response to student needs and feedback; · students’ progress and difficulties can be tracked and students will be able to record comments while using the modules. Tracking and students’ comments will allow teachers to discover areas of difficulty which can be addressed through small group work and also provide for a continuous cycle of development, use and evaluation; · the modular construction makes sections of the program interchangeable between disciplines and allows academic staff to build courses by drawing on small modules of relevant content instead of large blocks of content comprising significant amounts of irrelevant material

Isolation and characterization of SPOROMUSA ACIDOVORANS sp. nov., a methylogrophic homoacetogenic bacterium

SPOROMUSA ACIDOVORANS sp. nov. was isolated from a pilot fermenter inoculated with effluent sample from the alcohol distillation industry. The isolate was a Gram-negative, motile, curved, spore-forming rod. The DNA base composition was 42 % G+C. The temperature range for growth was 20 to 40°C, with an optimum at 35°C ; growth occurred within a pH range of 5.4 to 7.5, with an optimum at pH 6.5. Growth substrates included methanol, H2-CO2, formate, fructose, ribose, fumarate, succinate and glycerol. Yeast extract was required for growth. The organism performed the homoacetogenic reaction. (Résumé d'auteur

Surface Percolation for Soil Improvement by Biocementation Utilizing In Situ Enriched Indigenous Aerobic and Anaerobic Ureolytic Soil Microorganisms

The use of biocementation via microbially induced carbonate precipitation (MICP) for improving the mechanical properties of weak soils in the laboratory has gained increased attention in recent years. This study proposes an approach for applying biocementation in situ, by combining the surface percolation of nutrients and cementation solution (urea/CaCl2) with in situ cultivation of indigenous soil urease positive microorganisms under non-sterile conditions. The enrichment of indigenous ureolytic soil bacteria was firstly tested in batch reactors. Using selective conditions (i.e., pH of 10 and urea concentrations of 0.17 M), highly active ureolytic microorganisms were enriched from four diverse soil samples under both oxygen-limited (anoxic) and oxygen-free (strictly anaerobic) conditions, providing final urease activities of more than 10 and 5 U/mL, respectively. The enrichment of indigenous ureolytic soil microorganisms was secondly tested in pure silica sand columns (300 and 1000 mm) for biocementation applications using the surface percolation approach. By applying the same selective conditions, the indigenous ureolytic soil microorganisms with high urease activity were also successfully enriched for both the fine and coarse sand columns. However, the in situ enriched urease activity was highly related to the dissolved oxygen of the percolated growth medium. The results showed that the in situ cultivated urease activity may produce non-clogging cementation over the entire 1000-mm columns, with unconfined compressive strength varying between 850–1560 kPa (for coarse sand) and 150–700 kPa (for fine sand), after 10 subsequent applications of cementation solution. The typically observed loss of ureolytic activity during the repeated application of the cementation solution was recovered by providing more growth medium under selective enrichment conditions, enabling the in situ enriched ureolytic microorganisms to increase in numbers and urease activity in such a way that continued cementation was possible

Contribution a l'etude du metabolisme de H2 par les bacteries anaerobies

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

A Periplasmic and Extracellular c-Type Cytochrome of Geobacter sulfurreducens Acts as a Ferric Iron Reductase and as an Electron Carrier to Other Acceptors or to Partner Bacteria

An extracellular electron carrier excreted into the growth medium by cells of Geobacter sulfurreducens was identified as a c-type cytochrome. The cytochrome was found to be distributed in about equal amounts in the membrane fraction, the periplasmic space, and the surrounding medium during all phases of growth with acetate plus fumarate. It was isolated from periplasmic preparations and purified to homogeneity by cationexchange chromatography, gel filtration, and hydrophobic interaction chromatography. The electrophoretically homogeneous cytochrome had a molecular mass of 9.57 6 0.02 kDa and exhibited in its reduced state absorption maxima at wavelengths of 552, 522, and 419 nm. The midpoint redox potential determined by redox titration was 20.167 V. With respect to molecular mass, redox properties, and molecular features, this cytochrome exhibited its highest similarity to the cytochromes c of Desulfovibrio salexigens and Desulfuromonas acetoxidans. The G. sulfurreducens cytochrome c reduced ferrihydrite (Fe(OH)3), Fe(III) nitrilotriacetic acid, Fe(III) citrate, and manganese dioxide at high rates. Elemental sulfur, anthraquinone disulfonate, and humic acids were reduced more slowly. G. sulfurreducens reduced the cytochrome with acetate as an electron donor and oxidized it with fumarate. Wolinella succinogenes was able to reduce externally provided cytochrome c of G. sulfurreducens with molecular hydrogen or formate as an electron donor and oxidized it with fumarate or nitrate as an electron acceptor. A coculture could be established in which G. sulfurreducens reduced the cytochrome with acetate, and the reduced cytochrome was reoxidized by W. succinogenes in the presence of nitrate. We conclude that this cytochrome can act as iron(III) reductase for electron transfer to insoluble iron hydroxides or to sulfur, manganese dioxide, or other oxidized compounds, and it can transfer electrons to partner bacteria

A Periplasmic and Extracellular c-Type Cytochrome of Geobacter sulfurreducens Acts as a Ferric Iron Reductase and as an Electron Carrier to Other Acceptors or to Partner Bacteria

An extracellular electron carrier excreted into the growth medium by cells of Geobacter sulfurreducens was identified as a c-type cytochrome. The cytochrome was found to be distributed in about equal amounts in the membrane fraction, the periplasmic space, and the surrounding medium during all phases of growth with acetate plus fumarate. It was isolated from periplasmic preparations and purified to homogeneity by cation-exchange chromatography, gel filtration, and hydrophobic interaction chromatography. The electrophoretically homogeneous cytochrome had a molecular mass of 9.57 ± 0.02 kDa and exhibited in its reduced state absorption maxima at wavelengths of 552, 522, and 419 nm. The midpoint redox potential determined by redox titration was −0.167 V. With respect to molecular mass, redox properties, and molecular features, this cytochrome exhibited its highest similarity to the cytochromes c of Desulfovibrio salexigens and Desulfuromonas acetoxidans. The G. sulfurreducens cytochrome c reduced ferrihydrite (Fe(OH)(3)), Fe(III) nitrilotriacetic acid, Fe(III) citrate, and manganese dioxide at high rates. Elemental sulfur, anthraquinone disulfonate, and humic acids were reduced more slowly. G. sulfurreducens reduced the cytochrome with acetate as an electron donor and oxidized it with fumarate. Wolinella succinogenes was able to reduce externally provided cytochrome c of G. sulfurreducens with molecular hydrogen or formate as an electron donor and oxidized it with fumarate or nitrate as an electron acceptor. A coculture could be established in which G. sulfurreducens reduced the cytochrome with acetate, and the reduced cytochrome was reoxidized by W. succinogenes in the presence of nitrate. We conclude that this cytochrome can act as iron(III) reductase for electron transfer to insoluble iron hydroxides or to sulfur, manganese dioxide, or other oxidized compounds, and it can transfer electrons to partner bacteria