The Effect of Dissimilatory Manganese Reduction on Lactate Fermentation and Microbial Community Assembly

Fermentation and dissimilatory manganese (Mn) reduction are inter-related metabolic processes that microbes can perform in anoxic environments. Fermentation is less energetically favorable and is often not considered to compete for organic carbon with dissimilatory metal reduction. Therefore, the aim of our study was to investigate the outcome of the competition for lactate between fermentation and Mn oxide (birnessite) reduction in a mixed microbial community. A birnessite reducing enrichment culture was obtained from activated sludge with lactate and birnessite as the substrates. This enrichment was further used to test how various birnessite activities (0, 10, 20, and 40 mM) affected the rates of fermentation and metal reduction, as well as community composition. Increased birnessite activity led to a decrease of lactate consumption rate. Acetate and propionate were the main products. With increasing birnessite activity, the propionate/acetate ratio decreased from 1.4 to 0.47. Significant CO2 production was detected only in the absence of birnessite. In its presence, CO2 concentrations remained close to the background since most of the CO2 produced in these experiments was recovered as MnCO3. The Mn reduction efficiency (Mn(II) produced divided by birnessite added) was the highest at 10 mM birnessite added, where about 50% of added birnessite was reduced to Mn(II), whereas at 20 and 40 mM approximately 21 and 16% was reduced. The decreased birnessite reduction efficiency at higher birnessite activities points to inhibition by terminal electron acceptors and/or its toxicity which was also indicated by retarded lactate oxidation and decreased concentrations of microbial metabolites. Birnessite activity strongly affected microbial community structure. Firmicutes and Bacteroidetes were the most abundant phyla at 0 mM of birnessite. Their abundance was inversely correlated with birnessite concentration. The relative sequence abundance of Proteobacteria correlated with birnessite concentrations. Most of the enriched populations were involved in lactate/acetate or amino acid fermentation and the only previously known metal reducing genus detected was related to Shewanella sp. The sequencing data confirmed that lactate consumption coupled to metal reduction was only one of the processes occurring and did not outcompete fermentation processes

Uranium bearing dissolved organic matter in the porewaters of uranium contaminated lake sediments

Uranium (U) mobility in the environment strongly depends on its oxidation state and the presence of complexing agents such as inorganic carbon, phosphates, and dissolved organic matter (DOM). Despite the importance of DOM in U mobility, the exact mechanism is still poorly understood. Therefore, the aim of our investigation was to characterise sediment porewater DOM in two lakes in Ontario, Canada (Bow and Bentley Lakes) that were historically contaminated with U and propose possible composition of UO2-bearing DOM. Depth profiles of U concentrations in porewaters and total sediment digests reveal U levels of up to 1.3 mg L−1 in porewater and up to 0.8 mg−1 g in sediment. Depth profiles of U did not correlate with Fe, Mn, SO4 2−, or Eh profiles. Therefore, porewater DOM was analysed and taken into consideration as the primary source of U mobility. Porewater DOM in each sediment section (1 cm sections, 20 cm core length) was analysed by high-resolution electrospray ionisation mass spectrometry. PCA analyses of porewater DOM mass spectra showed grouping and clear separation of DOM in sediment sections with elevated U concentrations in comparison to sections with background U concentrations. Several criteria were set to characterise UO2-bearing DOM and more than 70 different molecules were found. The vast majority of these UO2-DOM compounds fell in the category of carboxyl-containing aliphatic molecules (H/C between 0.85 and 1.2 and O/C≤0.4) and had a mean value of m/z about 720

Variations in U concentrations and isotope signatures in two Canadian lakes impacted by U mining: A combination of anthropogenic and biogeochemical processes

Temporal and vertical variations in uranium (U) concentrations and U isotope (δ238U, ‰) signatures were examined in sediment cores collected seven times over a one year period, from two lakes in Ontario, Canada, which are contaminated with U by historical mining activities. Bow Lake is holomictic, experiencing seasonal anoxia, while the sediments of meromictic Bentley Lake are permanently anoxic. Average annual peak concentrations of U in Bow Lake subsurface sediments were approximately 300 μg L−1 and 600 μg g−1 in porewater and bulk sediments, respectively. Similar ranges of concentrations (900 μg L−1 and 600 μg g−1, respectively) were observed in Bentley Lake sediments. The exceedingly high levels of U observed in the porewaters of both lakes, as well as the seasonal variability in U levels, challenge the traditional paradigm regarding U chemistry, i.e., that reduced U(IV) should be insoluble under anoxic conditions. The average annual δ238U ‰ values at the sediment-water interface of both lakes were similar (i.e., 0.47 ± 0.09‰ and 0.50 ± 0.16‰, relative to IRMM-184). The deep sediments in both Bentley Lake and Bow Lake record U isotope composition with a typical fractionation of 0.6‰ relative to the surface water, confirming authigenic U accumulation, i.e., negligible contribution of particulate material from the tailings. Also, the δ238U values in porewater have an average offset of ca. −0.1‰ relative to bulk sediments in anoxic zones and are reversed in the oxic sediment layer

Uranium isotope fractionation during adsorption, (co) precipitation, and biotic reduction

Uranium contamination of surface environments is a problem associated with both U-ore extraction/processing and situations in which groundwater comes into contact with geological formations high in uranium. Apart from the environmental concerns about U contamination, its accumulation and isotope composition have been used in marine sediments as a paleoproxy of the Earth’s oxygenation history. Understanding U isotope geochemistry is then essential either to develop sustainable remediation procedures as well as for use in paleotracer applications. We report on parameters controlling U immobilization and U isotope fractionation by adsorption onto Mn/Fe oxides, precipitation with phosphate, and biotic reduction. The light U isotope (235U) is preferentially adsorbed on Mn/Fe oxides in an oxic system. When adsorbed onto Mn/Fe oxides, dissolved organic carbon and carbonate are the most efficient ligands limiting U binding resulting in slight differences in U isotope composition (δ238U = 0.22 ± 0.06‰) compared to the DOC/DIC-free configuration (δ238U = 0.39 ± 0.04‰). Uranium precipitation with phosphate does not induce isotope fractionation. In contrast, during U biotic reduction, the heavy U isotope (238U) is accumulated in reduced species (δ238U up to −1‰). The different trends of U isotope fractionation in oxic and anoxic environments makes its isotope composition a useful tracer for both environmental and paleogeochemical applications

Investigation of crude oil degradation using metal oxide anode-based microbial fuel cell

Oil industries generate large amount of oil wastewater worldwide and it is challenging to develop a sustainable technique to treat them due to the potential risk of contamination and recalcitrance. In this study, we employed microbial fuel cell to investigate biodegradation of crude oil with concomitant power generation. MnO2 coated anode was used to facilitate anoxic oil degradation due to better biofilm attachment, and fuel cell performance was compared with the uncoated carbon anode. Our study revealed that MFC with coated anode produced comparatively higher power density (47 mW m−2) than uncoated carbon anode (38 mW m−2), suggesting better removal of hydrocarbon components, also confirmed by oil-biodegradation studies (36% compared to 25.5% removal of total alkanes). The performance of the two cells was additionally evaluated by electrochemical, morphological, elemental and microbial community analysis. The prevalence of communities associated with hydrocarbon degradation and electrogenesis signify crude oil degradation with power generation.</p

Temperature responses of soil ammonia-oxidising archaea depend on pH

International audienceAmmonia oxidising archaea (AOA) are an abundant and ubiquitously distributed group of soil microorganisms and contribute significantly to nitrogen cycling processes. Soil pH has been identified as a major driver of AOA diversification, but other environmental factors may also be important. The aim of this study was to determine whether soil pH also influenced the temperature range of AOA activity in soil. This was assessed by determining rates of ammonification and net nitrification, and AOA abundance and community composition during incubation of soils with pH in the range 3.6–7.5 at 20, 30 or 40 °C for 30 days. Net nitrification was greatest at 20 or 30 °C, with variation in optimal temperature between soils, net nitrification was not detectable at 40 °C, and mineralisation was greatest at 40 °C. AOA community composition differed following incubation at 20° and 30 °C, presumably through selection and growth of populations with different temperature optima, and, at 40 °C, due to cell death. There was no significant relationship between thaumarchaeotal cell abundance and yield estimated using amoA and 16S rRNA genes, possibly due to amplification of 16S rRNA genes of non-ammonia-oxidising Thaumarchaeota. However, amoA gene abundance and yield were greater at 20 °C than 30 °C in the most acidic soils, with the opposite relationship for the most neutral soils. This is consistent with cultivated lower temperature optima for neutrophilic, rather than acidophilic soil AOA. The results indicate that pH-driven diversification may have consequences for other aspects of AOA physiology including temperature optima for growth and activity in the environment

Uranium Isotope Fractionation during Adsorption, (Co)precipitation, and Biotic Reduction

Uranium contamination of surface environments is a problem associated with both U-ore extraction/processing and situations in which groundwater comes into contact with geological formations high in uranium. Apart from the environmental concerns about U contamination, its accumulation and isotope composition have been used in marine sediments as a paleoproxy of the Earth’s oxygenation history. Understanding U isotope geochemistry is then essential either to develop sustainable remediation procedures as well as for use in paleotracer applications. We report on parameters controlling U immobilization and U isotope fractionation by adsorption onto Mn/Fe oxides, precipitation with phosphate, and biotic reduction. The light U isotope (²³⁵U) is preferentially adsorbed on Mn/Fe oxides in an oxic system. When adsorbed onto Mn/Fe oxides, dissolved organic carbon and carbonate are the most efficient ligands limiting U binding resulting in slight differences in U isotope composition (δ²³⁸U = 0.22 ± 0.06‰) compared to the DOC/DIC-free configuration (δ²³⁸U = 0.39 ± 0.04‰). Uranium precipitation with phosphate does not induce isotope fractionation. In contrast, during U biotic reduction, the heavy U isotope (²³⁸U) is accumulated in reduced species (δ²³⁸U up to −1‰). The different trends of U isotope fractionation in oxic and anoxic environments makes its isotope composition a useful tracer for both environmental and paleogeochemical applications

Can fossil fuel energy be recovered and used without any CO2 emissions to the atmosphere?

The world’s energy system is still dominated by fossil fuels. While there is a rapid reduction in the cost of renewable energy and the environmental costs of continued carbon dioxide emissions from fossil fuel recovery and use are well understood, current economic, infrastructure and political constraints sustain the fossil fuel enterprise as a dominant component of the energy system. Though routes to decarbonizing fossil fuel use, such as carbon capture and storage, have been proposed and have been demonstrated at commercial scale, current CCS CO2 storage quantities are very small and no large-scale practical route to providing fossil fuel energy, without the CO2 emissions attendant with fuel production and use has been proposed. Here we look at some of the boundary conditions and possible routes to production of emissions free energy from fossil fuels, and specifically petroleum reservoirs. Focusing on the production of electrical power we look at possible applications of microbially mediated hydrocarbon oxidation, coupled to a range of energy harvesting strategies, to the provision of electrical power at surface at a range of scales suitable for grid power provision, powering upstream oilfield facilities or for powering in situ sensing and exploration systems. We also ask the question, even if practical, would direct production of electrical power from oil and gas fields be a politically and economically sensible strategy as part of the energy transition away from traditional fossil fuel use

Can fossil fuel energy be recovered and used without any CO₂ emissions to the atmosphere?

The world’s energy system is still dominated by fossil fuels. While there is a rapid reduction in the cost of renewable energy and the environmental costs of continued carbon dioxide emissions from fossil fuel recovery and use are well understood, current economic, infrastructure and political constraints sustain the fossil fuel enterprise as a dominant component of the energy system. Though routes to decarbonizing fossil fuel use, such as carbon capture and storage, have been proposed and have been demonstrated at commercial scale, current CCS CO2 storage quantities are very small and no large-scale practical route to providing fossil fuel energy, without the CO2 emissions attendant with fuel production and use has been proposed. Here we look at some of the boundary conditions and possible routes to production of emissions free energy from fossil fuels, and specifically petroleum reservoirs. Focusing on the production of electrical power we look at possible applications of microbially mediated hydrocarbon oxidation, coupled to a range of energy harvesting strategies, to the provision of electrical power at surface at a range of scales suitable for grid power provision, powering upstream oilfield facilities or for powering in situ sensing and exploration systems. We also ask the question, even if practical, would direct production of electrical power from oil and gas fields be a politically and economically sensible strategy as part of the energy transition away from traditional fossil fuel use.</p