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    ItemOpen Access
    A method for 3D printing bio-cemented spatial structures using sand and urease active calcium carbonate powder
    (2020) Nething, Christoph; Smirnova, Maya; Gröning, Janosch A. D.; Haase, Walter; Stolz, Andreas; Sobek, Werner
    The substitution of Portland cement with microbially based bio-cement for the production of construction materials is an emerging sustainable technology. Bio-cemented building components such as bricks have been fabricated in molds, where bacteria-containing aggregates solidify when treated with a cementation solution. Thisrestricts component size due to the limitedfluid penetration depth and narrows options for component customization. The use of additive manufacturing technologies has the potential to overcome those limitations and toexpand the range of bio-cement applications. In the present work an automated process for the production ofspatial structures has been developed, in which sand and urease active calcium carbonate powder were selectively deposited within a print volumeand treatedwith a cementation solution.This method provided conditionsfor calcite precipitation in the powder-containing areas, whereas areas of pure sand served as removable supportstructure allowing improvedfluid exchange. The 3D printed structure was geometrically stable and had sharplydefined boundaries. Compressive strength tests on cylindricalspecimens showed thatthe used powder-sandmixwas suitable for the production of high-strength bio-cemented material. The present work demonstrates an application of bio-cement in an additive manufacturing process, that can potentially be used to produce resourceefficient sustainable building components.
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    ItemOpen Access
    Degradation of fluorene by Brevibacterium sp. strain DPO 1361: a novel C-C bond cleavage mechanism via 1,10-dihydro-1,10-dihydroxyfluoren-9-one
    (1994) Trenz, Stefan Peter; Engesser, Karl-Heinrich; Fischer, Peter; Knackmuss, Hans-Joachim
    Angular dioxygenation has been established as the crucial step in dibenzofuran degradation by Brevibacterium sp. strain DPO 1361 (V. Strubel, K. H. Engesser, P. Fischer, and H.-J. Knackmuss, J. Bacteriol. 173:1932-1937, 1991). The same strain utilizes biphenyl and fluorene as sole sources of carbon and energy. The fluorene degradation sequence is proposed to be initiated by oxidation of the fluorene methylene group to 9-fluorenol. Cells grown on fluorene exhibit pronounced 9-fluorenol dehydrogenase activity. Angular dioxygenation of the 9-fluorenone thus formed yields 1,10-dihydro-1,10-dihydroxyfluoren-9-one (DDF). A mechanistic model is presented for the subsequent C-C bond cleavage by an NAD(+)-dependent DDF dehydrogenase, acting on the angular dihydrodiol. This enzyme was purified and characterized as a tetramer of four identical 40-kDa subunits. The following Km values were determined: 13 microM for DDF and 65 microM for 2,3-dihydro-2,3-dihydroxybiphenyl. The enzyme also catalyzes the production of 3-(2'-carboxyphenyl)catechol, which was isolated, and structurally characterized, in the form of the corresponding lactone, 4-hydroxydibenzo-(b,d)-pyran-6-one. Stoichiometry analysis unequivocally demonstrates that angular dioxygenation constitutes the principal pathway in Brevibacterium sp. strain DPO 1361.