Incomplete Wood-Ljungdahl pathway facilitates one-carbon metabolism in organohalide-respiring Dehalococcoides mccartyi.

The acetyl-CoA "Wood-Ljungdahl" pathway couples the folate-mediated one-carbon (C1) metabolism to either CO2 reduction or acetate oxidation via acetyl-CoA. This pathway is distributed in diverse anaerobes and is used for both energy conservation and assimilation of C1 compounds. Genome annotations for all sequenced strains of Dehalococcoides mccartyi, an important bacterium involved in the bioremediation of chlorinated solvents, reveal homologous genes encoding an incomplete Wood-Ljungdahl pathway. Because this pathway lacks key enzymes for both C1 metabolism and CO2 reduction, its cellular functions remain elusive. Here we used D. mccartyi strain 195 as a model organism to investigate the metabolic function of this pathway and its impacts on the growth of strain 195. Surprisingly, this pathway cleaves acetyl-CoA to donate a methyl group for production of methyl-tetrahydrofolate (CH3-THF) for methionine biosynthesis, representing an unconventional strategy for generating CH3-THF in organisms without methylene-tetrahydrofolate reductase. Carbon monoxide (CO) was found to accumulate as an obligate by-product from the acetyl-CoA cleavage because of the lack of a CO dehydrogenase in strain 195. CO accumulation inhibits the sustainable growth and dechlorination of strain 195 maintained in pure cultures, but can be prevented by CO-metabolizing anaerobes that coexist with D. mccartyi, resulting in an unusual syntrophic association. We also found that this pathway incorporates exogenous formate to support serine biosynthesis. This study of the incomplete Wood-Ljungdahl pathway in D. mccartyi indicates a unique bacterial C1 metabolism that is critical for D. mccartyi growth and interactions in dechlorinating communities and may play a role in other anaerobic communities

Inhibition of microbial sulfate reduction in a flow-through column system by (per)chlorate treatment.

Microbial sulfate reduction is a primary cause of oil reservoir souring. Here we show that amendment with chlorate or perchlorate [collectively (per)chlorate] potentially resolves this issue. Triplicate packed columns inoculated with marine sediment were flushed with coastal water amended with yeast extract and one of nitrate, chlorate, or perchlorate. Results showed that although sulfide production was dramatically reduced by all treatments, effluent sulfide was observed in the nitrate (10 mM) treatment after an initial inhibition period. In contrast, no effluent sulfide was observed with (per)chlorate (10 mM). Microbial community analyses indicated temporal community shifts and phylogenetic clustering by treatment. Nitrate addition stimulated Xanthomonadaceae and Rhizobiaceae growth, supporting their role in nitrate metabolism. (Per)chlorate showed distinct effects on microbial community structure compared with nitrate and resulted in a general suppression of the community relative to the untreated control combined with a significant decrease in sulfate reducing species abundance indicating specific toxicity. Furthermore, chlorate stimulated Pseudomonadaceae and Pseudoalteromonadaceae, members of which are known chlorate respirers, suggesting that chlorate may also control sulfidogenesis by biocompetitive exclusion of sulfate-reduction. Perchlorate addition stimulated Desulfobulbaceae and Desulfomonadaceae, which contain sulfide oxidizing and elemental sulfur-reducing species respectively, suggesting that effluent sulfide concentrations may be controlled through sulfur redox cycling in addition to toxicity and biocompetitive exclusion. Sulfur isotope analyses further support sulfur cycling in the columns, even when sulfide is not detected. This study indicates that (per)chlorate show great promise as inhibitors of sulfidogenesis in natural communities and provides insight into which organisms and respiratory processes are involved

Isotopic Tracking of Hanford 300 Area Derived Uranium in the Columbia River

Our objectives in this study are to quantify the discharge rate of uranium (U) to the Columbia River from the Hanford Site's 300 Area, and to follow that U down river to constrain its fate. Uranium from the Hanford Site has variable isotopic composition due to nuclear industrial processes carried out at the site. This characteristic makes it possible to use high-precision isotopic measurements of U in environmental samples to identify even trace levels of contaminant U, determine its sources, and estimate discharge rates. Our data on river water samples indicate that as much as 3.2 kg/day can enter the Columbia River from the 300 Area, which is only a small fraction of the total load of dissolved natural background U carried by the Columbia River. This very low-level of Hanford derived U can be discerned, despite dilution to < 1 percent of natural background U, 350 km downstream from the Hanford Site. These results indicate that isotopic methods can allow the amounts of U from the 300 Area of the Hanford Site entering the Columbia River to be measured accurately to ascertain whether they are an environmental concern, or are insignificant relative to natural uranium background in the Columbia River

Tris(Ethylenediamine)Cobalt(III) Nonaiododibismuthate

The asymmetric unit of the title compound, [Co(C2H8N2)3][Bi2I9], crystallizes in the orthorhombic space group Cmc21. The asymmetric unit contains half of a [Co(en)3]3+ cation (en is ethylenediamine) and half of a [Bi2I9]3- anion. Both species are located on mirror planes, requiring the [Co(en)3]3+ cation to be present as a statistically disordered mixture of both enantiomeric forms. Crystals were grown solvothermally from an ethanol-water solvent mixture using rac-[Co(en)3]I3 and bismuth triiodide as starting materials. The compound is a rare example of a mixed-metal halobismuthate material

Three unique coordination geometries involving 1,2-dimethoxy-4,5-bis(2-pyridylethynyl)benzene

Reaction of the new ligand 1,2-dimethoxy-4,5-bis(2-pyridylethynyl) benzene with different metal centers under similar reaction conditions led to three distinct structure formation processes: molecular ring closure, dimerization, and polymer formation

Disinhibition in Risky Sexual Behavior in Men, but Not Women, during Four Years of Antiretroviral Therapy in Rural, Southwestern Uganda

Background: In resource-rich areas, risky sexual behavior (RSB) largely diminishes after initiation of anti-retroviral therapy, with notable exceptions among some populations who perceive a protected benefit from anti-retroviral therapy (ART). Yet, there is limited data about long-term trends in risky sexual behavior among HIV-infected people in sub-Saharan Africa after initiation of anti-retroviral therapy. Methods: We administered questionnaires every three months to collect sexual behavior data among patients taking ART in southwestern Uganda over four years of follow-up time. We defined RSB as having unprotected sex with an HIV-negative or unknown status partner, or unprotected sex with a casual partner. We fit logistic regression models to estimate changes in RSB by time on ART, with and without adjustment for calendar year and CD4 count. Results: 506 participants were enrolled between 2005 and 2011 and contributed a median of 13 visits and 3.5 years of observation time. The majority were female (70%) and median age was 34 years (interquartile range 29–39). There was a decrease in the proportion of men reporting RSB from the pre-ART visit to the first post-ART visit (16.2 to 4.3%, p<0.01) but not women (14.1 to 13.3%, p = 0.80). With each year of ART, women reported decreasing RSB (OR 0.85 per year, 95%CI 0.74–0.98, p = 0.03). In contrast, men had increasing odds of reporting RSB with each year of ART to near pre-treatment rates (OR 1.41, 95%CI 1.14–1.74, p = 0.001), which was partially confounded by changes in calendar time and CD4 count (AOR = 1.24, 95%CI 0.92–1.67, p = 0.16). Conclusions: Men in southwestern Uganda reported increasing RSB over four years on ART, to levels approaching pre-treatment rates. Strategies to promote long-term safe sex practices targeted to HIV-infected men on ART might have a significant impact on preventing HIV transmission in this setting

Isotopic Tracers for Biogeochemical Processes and Contaminant Transport: Hanford, Washington

Our goal is to use isotopic measurements to understand how contaminants are introduced to and stored in the vadose zone, and what processes control migration from the vadose zone to groundwater and then to surface water. We have been using the Hanford Site in south-central Washington as our field laboratory, and our investigations are often stimulated by observations made as part of the groundwater monitoring program and vadose zone characterization activities. Understanding the transport of contaminants at Hanford is difficult due to the presence of multiple potential sources within small areas, the long history of activities, the range of disposal methods, and the continuing evolution of the hydrological system. Observations often do not conform to simple models, and cannot be adequately understood with standard characterization approaches, even though the characterization activities are quite extensive. One of our objectives is to test the value of adding isotopic techniques to the characterization program, which has the immediate potential benefit of addressing specific remediation issues, but more importantly, it allows us to study fundamental processes at the scale and in the medium where they need to be understood. Here we focus on two recent studies at the waste management area (WMA) T-TX-TY, which relate to the sources and transport histories of vadose zone and groundwater contamination and contaminant fluid-sediment interaction. The WMA-T and WMA-TX-TY tank farms are located within the 200 West Area in the central portion of the Hanford Site (Fig. 2). They present a complicated picture of mixed groundwater plumes of nitrate, {sup 99}Tc, Cr{sup 6+}, carbon tetrachloride, etc. and multiple potential vadose zone sources such as tank leaks and disposal cribs (Fig. 3). To access potential vadose zone sources, we analyzed samples from cores C3832 near tank TX-104 and from C4104 near tank T-106. Tank T-106 was involved in a major event in 1973 in which 435,000 L of high activity waste leaked to the vadose zone over a seven-week period. Other nearby tanks (T-103 and T-101) are also suspected of having leaked or overfilled. Pore water from these cores was analyzed for U and Sr isotopic compositions. Increasing {sup 99}Tc concentration in monitoring well 299-W11-39 (to 27,000 pCi/L in 2005) near the northeast corner of the WMA-T area prompted the emplacement of a series of new wells, 299-W11-25B, W11-45 (down gradient), and W11-47 (Fig. 3), during which depth discrete samples were collected below the groundwater surface. The depth profile from W11-25B revealed high {sup 99}Tc concentrations peaking at 182,000 pCi/L at {approx}10 m below the water table (Dresel et al. 2006). We obtained aliquots for isotopic analysis of groundwater samples produced by purge-and-pump sampling during the drilling of W11-25B, -45 and -47. In addition we have analyzed groundwater samples from monitoring wells in the vicinity of WMA T-TX-TY

Reactive transport model of sulfur cycling as impacted by perchlorate and nitrate treatments

Microbial souring in oil reservoirs produces toxic, corrosive hydrogen sulfide through microbial sulfate reduction, often accompanying (sea)­water flooding during secondary oil recovery. With data from column experiments as constraints, we developed the first reactive-transport model of a new candidate inhibitor, perchlorate, and compared it with the commonly used inhibitor, nitrate. Our model provided a good fit to the data, which suggest that perchlorate is more effective than nitrate on a per mole of inhibitor basis. Critically, we used our model to gain insight into the underlying competing mechanisms controlling the action of each inhibitor. This analysis suggested that competition by heterotrophic perchlorate reducers and direct inhibition by nitrite produced from heterotrophic nitrate reduction were the most important mechanisms for the perchlorate and nitrate treatments, respectively, in the modeled column experiments. This work demonstrates modeling to be a powerful tool for increasing and testing our understanding of reservoir-souring generation, prevention, and remediation processes, allowing us to incorporate insights derived from laboratory experiments into a framework that can potentially be used to assess risk and design optimal treatment schemes