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To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1574-6941.2007.00401.x Byline: Steffi Herrmann (1), Sabine Kleinsteuber (2), Thomas R. Neu (3), Hans Hermann Richnow (1), Carsten Vogt (1) Keywords: benzene; sulfate-reducing conditions; anaerobic degradation; natural attenuation Abstract: Abstract Microcosms filled with different solids (sand, lava, Amberlite XAD-7) were exposed for 67 days in the sulfidic part of a groundwater monitoring well downstream of the source zone of a benzene-contaminated aquifer and subsequently incubated in the laboratory. Benzene was repeatedly degraded in several microcosms accompanied by production of sulfide, leading to stable benzene-degrading enrichment cultures. In control microcosms without filling material, benzene was initially degraded, but the benzene-degrading capacity could not be sustained. The results indicate that long-term physiologically active benzene-degrading microorganisms were attached to surfaces of the solids. The biodiversity and attachment behavior of microorganisms in the in situ microcosms was assessed by confocal laser scanning microscopy and single-strand conformation polymorphism (SSCP) analysis, followed by sequencing of dominant SSCP bands. The microbial community was composed of several different Bacteria, representing members of Clostridia, Bacteroidales, all subgroups of the Proteobacteria, Verrucomicrobia, Nitrospira, Chloroflexi and Chlorobi. Only a few archaeal sequences could be retrieved from the communities. The majority of phylotypes were affiliated to bacterial groups with a possible functional relationship to the bacterial sulfur cycle, thus indicating that the microbial community in the investigated aquifer zone depends mainly on inorganic sulfur compounds as electron donors or acceptors, a finding that corresponds to the geochemical data. Author Affiliation: (1)Department of Isotope Biogeochemistry, UFZ - Helmholtz Centre for Environmental Research, Leipzig, Germany (2)Department of Environmental Microbiology, UFZ - Helmholtz Centre for Environmental Research, Leipzig, Germany (3)Department of River Ecology, UFZ - Helmholtz Centre for Environmental Research, Magdeburg, Germany Article History: Received 19 April 2007; revised 12 September 2007; accepted 20 September 2007.First published online December 2007. Article note: Correspondence: Carsten Vogt, Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstra[sz]e 15, D-04318 Leipzig, Germany. Tel.: +49 341 235 1317; fax: +49 341 235 1443; e-mail: carsten.vogt@ufz.de