Batch culture experiments were performed with 32 different sulfate-reducing prokaryotes to explore the diversity in sulfur isotope fractionation during dissimilatory sulfate reduction by pure cultures. The selected strains reflect the phylogenetic and physiologic diversity of presently known sulfate reducers and cover a broad range of natural marine and freshwater habitats. Experimental conditions were designed to achieve optimum growth conditions with respect to electron donors, salinity, temperature, and pH. Under these optimized conditions, experimental fractionation factors ranged from 2.0 to 42.0‰. Salinity, incubation temperature, pH, and phylogeny had no systematic effect on the sulfur isotope fractionation. There was no correlation between isotope fractionation and sulfate reduction rate. The type of dissimilatory bisulfite reductase also had no effect on fractionation. Sulfate reducers that oxidized the carbon source completely to CO 2 showed greater fractionations than sulfate reducers that released acetate as the final product of carbon oxidation. Different metabolic pathways and variable regulation of sulfate transport across the cell membrane all potentially affect isotope fractionation. Previous models that explained fractionation only in terms of sulfate reduction rates appear to be oversimplified. The species-specific physiology of each sulfate reducer thus needs to be taken into account to understand the regulation of sulfur isotope fractionation during dissimilatory sulfate reduction.The stable sulfur isotope ratio between 32 S and 34 S of solid and dissolved sulfur compounds is widely used as a marker for bacterial sulfate reduction and bacterial processes associated with the recycling of sulfide (5,8,18). The reduction of sulfate by sulfate reducers is coupled to a pronounced enrichment of 32 S in the produced sulfide. However, the extent of the isotope enrichment remains a matter of ongoing debate. Results from batch-culture, continuous-culture, and resting-cell experiments suggested that the isotope enrichment is inversely proportional to sulfate reduction rates (9,22,23). Furthermore, below a threshold concentration of sulfate, the discrimination against 34 S apparently decreases (21). Previous experimental studies of the isotope fractionation were conducted with only a few selected species that were known at that time, mainly Desulfovibrio spp. and two Desulfotomaculum spp. (9,15,22,28). Moreover, since most of these species were isolated from freshwater environments, they are not necessarily of ecological importance in marine environments.The different electron donors used in these early pure-culture studies included ethanol, lactate, acetate, pyruvate, glucose, yeast extract, and hydrogen (22, 23). Today, a number of sulfate reducers are known that can metabolize a wide range of substrates including long-chain fatty acids, alcohols, and even aromatic compounds that represent relevant substrates for natural environments (33,45,47). Hydrogen, propionate, butyrate, and acetate appear to be...

The hydrochemistry and the microbial diversity of a pristine aquifer system near Garzweiler, Germany, were characterized. Hydrogeochemical and isotopic data indicate a recent activity of sulfate-reducing bacteria in the Tertiary marine sands. The community structure in the aquifer was studied by fluorescence in situ hybridization (FISH). Up to 7.3 x 10(5) cells/mL were detected by DAPI-staining. Bacteria (identified by the probe EUB338) were dominant, representing 51.9% of the total cell number (DAPI). Another 25.7% of total cell were affiliated with the domain Archaea as identified by the probe ARCH915. Within the domain Bacteria, the beta-Proteobacteria were most abundant (21.0% of total cell counts). Using genus-specific probes for sulfate-reducing bacteria (SRB), 2.5% of the total cells were identified as members of the genus Desulfotomaculum. This reflects the predominant role these microorganisms have been found to play in sulfate-reducing zones of aquifers at other sites. Previously, all SRB cultured from this site were from the spore-forming genera Desulfotomaculum and Desulfosporosinus.

In a combined isotope geochemical and microbiological investigation, a setting of multiple aquifers was characterized. Biologically mediated redox processes were observed in the aquifers situated in marine sands of Tertiary age and overlying Quaternary gravel deposits. Intercalated lignite seams define the aquitards, which separate the aquifers. Bacterial oxidation of organic matter is evident from dissolved inorganic carbon characterized by average carbon isotope values between ?18.4 per thousand and ?15.7 per thousand (PDB). Strongly positive sulfur isotope values of up to +50 per thousand (CTD) for residual sulfate indicate sulfate reduction under closed system conditions with respect to sulfate availability. Both, hydrochemical and isotope data are thus consistent with the recent activity of sulfate-reducing bacteria (SRB). Microbiological investigations revealed the presence of an anaerobic food chain in the aquifers. Most-probable-number (MPN) determinations for SRB and fermenting microorganisms reached highest values at the interface between aquifer and lignite seam (1.5 x 103 cells/g sediment dry mass). Five strains of SRB were isolated from highest MPN dilutions. Spore-forming bacteria appeared to dominate the SRB population. Sulfate reduction rates were determined by the 35S-radiotracer method. A detailed assessment indicates an increase in the reduction rate in proximity to the lignite seam, with a maximum turnover of 8.4 mM sulfate/a, suggesting that lignite-drived compounds represent the substrate for sulfate reduction.

Immune evasion is a hallmark of cancer and the presence and interaction of immune cells within a tumor and its microenvironment can have a great impact on disease progression and prognosis. Unravelling the complex interplay of neoplastic and immune cells requires both phenotypic and spatial analysis of each involved cell population in the tissue. The aim of this study is to compare 3 methods of biomarker analysis in tissues, flow cytometry, immunohistochemistry (IHC) and Chipcytometry, in their ability to detect immune cells in a tumor model. NOD-Scid tg HLA-A2.1 mice were implanted with human Ma-Mel-19 melanoma cells. After 21 days, the mice were injected with human PBMC at the tumor site. Local treatment with Tasquinimod was performed three times once a week. Tumors, including the neighbouring PBMC injection site were excised on day 48 and immune cell content was analysed by Chipcytometry, flow cytometry and IHC. All three methods were successful in detecting human immune cells in the samples consisting mostly of T-cells (CD45+CD3+). However, flow cytometry and IHC were unable to provide either accurate localization or phenotyping data, respectively. With Chipcytometry we were able to specifically quantify tumor-infiltrating immune cells. In treated samples immune cell count (110/mm^2) and composition (72% T-cells) was significantly higher than in the untreated samples (54/mm^2, 49% T-cells). We show that Chipcytometry is able to produce “flow-like” quantitative data, while also retaining spatial information. This makes Chipcytometry a powerful tool for the study of immunological processes in tumors.

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