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Inorganic Chemical Pollutants
Published in William J. Rea, Kalpana D. Patel, Reversibility of Chronic Disease and Hypersensitivity, Volume 4, 2017
William J. Rea, Kalpana D. Patel
MeHg is a potent neurotoxin produced in natural environments from inorganic mercury by anaerobic bacteria. However, until now, the genes and proteins involved have remained unidentified. Parks et al.550 report a two-gene cluster, hgcA and hgcB, required for mercury methylation by Desulfovibrio desulfuricans ND132 and Geobacter sulfurreducens PCA. In either bacterium, deletion of hgcA, hgcB, or both genes abolishes mercury methylation. The genes encode a putative corrinoid protein, HgcA, and a 2 (4Fe-4S) ferredoxin, HgcB, consistent with roles as a methyl carrier and an electron donor required for corrinoid cofactor reduction, respectively. Among bacteria and archaea with sequenced genomes, gene orthologs are present in confirmed methylators but absent in nonmethylators, suggesting a common mercury methylation pathway in all methylating bacteria and archaea sequenced to date.
Radionuclide Concentrations in Soils lution-Processed Organic Solar Cells
Published in Michael Pöschl, Leo M. L. Nollet, Radionuclide Concentrations in Food and the Environment, 2006
The reduction of Tc(VII) to Tc(IV) is caused by bacteria such as Shewanella putrefaciens [19], Geobacter sulfurreducens [20], and some sulfate-reducing bacteria [21] under strict anaerobic conditions. In addition to the technetium reduction, Geobacter metallireducens produces insoluble technetium precipitate. These technetium-reducing anaerobic bacteria are often found in soils under waterlogged conditions (e.g., paddy fields) [22]. The presence of such technetium-reducing anaerobic bacteria in paddy soils raises the expectations of reduction and precipitation of technetium in the water covering these soils.
Characterization of the biofilm grown on 304L stainless steel in urban wastewaters: extracellular polymeric substances (EPS) and bacterial consortia
Published in Biofouling, 2020
Islem Ziadi, Leila El-Bassi, Latifa Bousselmi, Hanene Akrout
In 7 day aged biofilm for the UTUWW, three IB strains were identified: Geobacter bemidjiensis (strain IB3; MK778891), Terriglobus sinensis (strain IB4; MK778927) and Edaphobacter dinghuensis (strain IB5, MK779009). The strain Geobacter bemidjiensis (stain IB10; MK775265) was also isolated from the biofilm grown in the TUWW at the same sampling time. It has been demonstrated that this strain is able to reduce iron but also cause the dissolution and alteration of oxides and hydroxides and consequently accelerates the corrosion attack (Luef et al. 2013). The strains IB4 and IB5 are members of the phylum, acid-bacteria, leading to the oxidation of pyrite (FeS2) to form sulfuric acid and ferrous iron. The produced sulfuric acid-induced pH increases and consequently, ferrous iron is oxidized to ferric iron (Wegner and Liesack 2017).
Bulk phase resource ratio alters carbon steel corrosion rates and endogenously produced extracellular electron transfer mediators in a sulfate-reducing biofilm
Published in Biofouling, 2019
Gregory P. Krantz, Kilean Lucas, Erica L.- Wunderlich, Linh T. Hoang, Recep Avci, Gary Siuzdak, Matthew W. Fields
Extracellular electron transfer, which is shown to enhance MIC, is now recognized as a more widespread microbial phenotype, suggesting that EET-MIC could be a major mechanism for biocorrosion worldwide (Nealson and Saffarini, 1994; Kato 2016; Huang et al. 2018). Previous work postulated that some SRBs contribute to MIC under various growth conditions through Fe0 oxidation via interactions with CS (Gu, 2012; Venzlaff et al. 2013; Enning and Garrelfs 2014; Li et al. 2015). In addition to heme redox centers of cytochromes, cell-secreted molecules have been shown to serve as electron carriers in EET processes in both Shewanella oneidensis and Geobacter sulfurreducens (Marsili et al. 2008; Okamoto et al. 2014), and, more recently, flavin mononucleotide (FMN) and riboflavin were proposed to function in a diffusion-based EET (2 e−) or bifurcated direct EET (1 e−) in Shewanella (Okamoto et al. 2014). Therefore, future work should focus on elucidating the physiological conditions under which EET mechanisms contribute to overall biocorrosion.
Continuous flow system for biofilm formation using controlled concentrations of Pseudomonas putida from chicken carcass and coupled to electrochemical impedance detection
Published in Biofouling, 2020
Daoyuan Yang, José I. Reyes-De-Corcuera
Based on the Randles circuit model, the Rct decreased by 61, 56 or 30 kΩ from 207 ± 12, 222 ± 12 or 206 ± 2 kΩ at time 0 to 146 ± 2 at 63 h, 166 ± 7 at 49 h or 176 ± 3 kΩ at 12 h corresponding to 10,000-fold, 1,000-fold or 100-fold dilution, respectively. Based on the biofilm model, the Rb decreased from 208 ± 12, 223 ± 12 or 207 ± 2 kΩ at time 0 to 146 ± 2 at 63 h, 166 ± 7 at 49 h or 176 ± 3 kΩ at 12 h corresponding to 10,000-fold, 1,000-fold or 100-fold dilution, respectively. The decrease in Rct as the biofilm grew is in agreement with many other reports (Bayoudh et al. 2008; Xu et al. 2010; Malvankar, Tuominen et al. 2012; Babauta and Beyenal 2017). The decrease in Rct might come from the charge transfer increase resulting from the attachment of charged bacterial cells (Dheilly et al. 2008). The decrease in Rct might also be related to the increase in the biofilm conductivity. Malvankar, Tuominen et al. (2012) suggested that the Rct, which arose from the activation barrier at the interface of biofilm and electrode, was lowered when the electrons carried more energy after passing through a more conductive biofilm. The biofilm may become more conductive as it grows and results in the decrease in Rct (Babauta and Beyenal 2017). However, physical and physiological interpretation of equivalent circuits are not straightforward. Furthermore, the electrochemical properties of a biofilm depend on the microbes that form the biofilm. The conductivity of biofilm varies with the microbial strain. Geobacter sulfurreducens, Pseudomonas stutzeri and Staphylococcus epidermidis formed conductive biofilms (Bayoudh et al. 2008; Babauta and Beyenal 2017). But biofilms of Pseudomonas aeruginosa, Bacillus subtilis, and Escherichia coli had low conductivity (Dheilly et al. 2008; Malvankar, Lau et al. 2012). If the biofilm is poorly conducting, the cells attached to the surface become an insulating barrier inhibiting the charge transfer and a higher Rct can be detected by EIS. In addition, the ionic strength of the electrolyte also needs to be taken into consideration. The EIS response to the formation and the dynamics of mixed-culture biofilms has not yet been characterized.