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A novel sulfate-reducing bacterium was isolated from pristine sediments of Lake Stechlin, Germany. This strain, STP12 T , was found to contain predominantly c-type cytochromes and to reduce sulfate, sulfite and thiosulfate using lactate as an electron donor. Although STP12 T could not utilize elemental sulfur as an electron acceptor, it could support growth by dissimilatory Fe(III) reduction. In a comparison of 16S rRNA gene sequences, STP12 T was 96?7 % similar to Desulfosporosinus auripigmenti DSM 13351 T , 96?5 % similar to Desulfosporosinus meridiei DSM 13257 T and 96?4 % similar to Desulfosporosinus orientis DSM 765 T . DNA-DNA hybridization experiments revealed that strain STP12 T shows only 32 % reassociation with the type strain of the type species of the genus, D. orientis DSM 765 T . These data, considered in conjunction with strain-specific differences in heavy metal tolerance, cell-wall chemotaxonomy and riboprint patterns, support recognition of strain STP12 T (=DSM 15449 T =JCM 12239 T ) as the type strain of a distinct and novel species within the genus Desulfosporosinus, Desulfosporosinus lacus sp. nov.The genus Desulfosporosinus currently contains three species with validly published names, Desulfosporosinus orientis (Stackebrandt et al., 1997), Desulfosporosinus auripigmenti (Stackebrandt et al., 2003) and Desulfosporosinus meridiei (Robertson et al., 2001). Isolates from locales separated by thousands of kilometres exist for some of these species (e.g. DSM 8344; Vainshtein et al., 1994). Culture-and nonculture-based studies have revealed the existence of Desulfosporosinus-like organisms in environmental settings as diverse as permafrost (Vainshtein et al., 1994), pristine aquifers (Detmers et al., 2004), municipal drinking water (Bade, 2000) and rice plant roots (Scheid et al., 2004).Multiple lines of evidence suggest that members of the genus also commonly inhabit industrially impacted soils and sediments. D. auripigmenti was isolated from an arseniccontaminated watershed, and is one of a limited number of bacteria known to respire arsenate (Newman et al., 1997). Recently, another arsenic-reducing Desulfosporosinus strain was isolated from arsenic-contaminated sediments; this organism has the capacity to metabolize a wide variety of aromatic compounds (Liu et al., 2004). Kusel et al. (2001) reported the isolation of Desulfosporosinus-like organisms from a coal-mining-impacted lake, while Robertson et al. (2000) isolated eight Desulfosporosinus strains from a hydrocarbon-contaminated soil. Two of these were later described as D. meridiei (Robertson et al., 2001) and their activity was linked to toluene mineralization (Robertson et al., 2000;Franzmann et al., 2002 et al., 2003), and uranium mine tailings in Shiprock, NM (Nevin et al., 2003). Significantly, enrichment of Desulfosporosinus-like microbes has been associated with stimulated removal of solution-phase uranium (Nevin et al., 2003). In such contexts, uranium precipitation may occur secondarily to sulfidogenesis or as a primary resul...

Ion-specific electrodes were used to study the binding of Hg(2+), Pb(2+), Cu(2+), and Cd(2+) ions to widely used bacterial growth media (Nutrient broth, trypticase soy broth, the medium of Foot and Taylor [6] and of Nelsonet al.[12]) and to media components [yeast extract, peptone, tryptone, proteose peptone, and casamino acids (acid hydrolyzed casein)]. Volatilization of Hg(2+) from aqueous solutions could be prevented by any of the growth media or their components. All media bound large amounts of Hg(2+), Pb(2+), and Cu(2+), but much less Cd(2+). Of the media components, casamino acids showed the most binding activity for all metal ions; the relative affinity of other media components to different ions varied with the cation studied. In general, the Irving-Williams [8] series for cation affinity to organic ligands was followed: Hg(2+)>Pa(2+)≫ Cu(2+)≫ Cd(2+).After adding 20 ppm of Hg(2+), Pb(2+), or Cu(2+) (concentrations inhibitory to the growth of most microorganisms) to the growth media, 80 ppb or less remained as free cations in the solution. This might suggest that such ions enter bacterial cells as organic complexes, or that bacterial cells can compete successfully with growth media for the bound ions.

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/ Experimental data for sorption of Hg, Cd, Cu, and Pb by sand, silt, and organic-rich sediments from the Ottawa River, Canada show significant conformity to Langmuir's equation. Values of the bonding energy constant and the sorption maximum correlate directly with organic content and mean grain size (q~). Desorption experiments indicate that the heavy metals form stable complexes in nitrilotriacetate (NTA) and NaCI Solutions, with the following desorption ratios: Hg, 1:1 (CI-:NTA); Pb, 1:10; Cd, 1:2. Serial and batch desorption studies under various conditions show that the cation-exchange order in the sediments is Hg > Pb > Cu > Cd. For a given heavy metal the partition coefficient between sediment and solution is not greatly changed by the presence of another cation, provided the latter has the same order of concentration. If, the concentration of one cation exceeds another by more than 10, however, significant desorption of the less concentrated ion takes place on a mass action basis.