Sulfate-reducing Bacterium Desulfovibrio Desulfuricans Research Articles

Substrate-dependent strategies to mitigate sulfate inhibition on microbial reductive dechlorination of polychlorinated biphenyls

Sulfate widely co-exists with polychlorinated biphenyls (PCBs) at various concentrations in the subsurface environment. Previous studies have suggested that sulfate often hampers microbial degradation of aliphatic chlorinated solvents such as chloroethenes. However, the impact of sulfate on microbial reductive dechlorination of aromatic PCBs and the underlying mechanisms have received limited attention. Likewise, strategies to mitigate such inhibition remain scarce. Here we found that the mechanisms and mitigation strategies of sulfate inhibition on PCB dechlorination were substrate-dependent. Under electron donor-limiting conditions, even a low concentration of sulfate (2 mM) resulted in a decreased PCB dechlorination rate by 88.7% in a co-culture comprising Dehalococcoides mccartyi CG1 and the sulfate-reducing bacterium Desulfovibrio desulfuricans F1, an inhibition which was attributed to the competition for electron donor between sulfate reduction and PCB dechlorination. As expected, re-amendment of 5 mM lactate effectively re-initiated PCB dechlorination. However, in the presence of a higher concentration of sulfate (5 mM), the PCB dechlorination rate in the co-culture was 77.7% lower than in the control, even with excessive electron donor supply. This inhibition was linked to high concentration of sulfide (∼5 mM) produced from sulfate reduction, as suggested by high availability of electron donor, recovery of dechlorination activity after removal of sulfide, and negligible influence of sulfate on PCB dechlorination in the axenic culture of D. mccartyi CG1. Indeed, sulfide (>5 mM) was found to directly suppress expression of PCB-dechlorinating reductive dehalogenase gene. The highest transcriptional level of pcbA1 was 2.9 ± 0.3 transcripts·cell−1 in the presence of ∼5 mM sulfide, which was increased to 37.4 ± 5.0 transcripts·cell−1 when sulfide was removed. Under this scenario, introduction of ferrous salts (5 mM) efficiently alleviated sulfide inhibition on PCB dechlorination. Interestingly, the augmentation of methanogens in the co-culture was also effective in mitigating sulfide inhibition on PCB dechlorination, offering a new approach to protect Dehalococcoides under sulfide stress. Collectively, these findings deepen our understanding of the influence of sulfate on microbial reductive dechlorination of PCBs and contribute to developing appropriate strategies based on geochemical conditions to alleviate sulfate inhibition during bioremediation of PCB-contaminated sites.

Investigating inhibition characteristics of Butea monosperma leaf extracts to retard stainless steel biocorrosion in the presence of sulfate-reducing bacteria

The influence of sulfate-reducing bacteria Desulfovibrio desulfuricans on stainless steel SS 202 corrosion in neutral media was studied in detail using weight loss and electrochemical routes. The bacterial activity resulted in material loss with an average rate of 0.015 mm/year. The scanning electron microscopy (SEM) analysis showed a significant increase in the sessile bacterial population with the immersion period. Use of 500 ppm palash (Butea monosperma) leaf extract (PLE) reduced the average corrosion rate to 0.002 mm/year. SEM analysis showed a very thin external film formation in the presence of the inhibitor. The X-ray photoelectron spectroscopy studies confirmed the presence of corrosion products such as Fe2O3 and FeS. The gas chromatography?mass spectrometry studies showed the dominant percentage of various terpenoids along with vitamin E as the main components of the PLE. Electrochemical analysis showed the existence of a diffusion barrier. The resistance offered by the diffusion barrier is high in the inhibited sample when compared to uninhibited samples.

Contrary effects of phytoplankton Chlorella vulgaris and its exudates on mercury methylation by iron- and sulfate-reducing bacteria

Mercury (Hg) is a pervasive environmental pollutant and poses serious health concerns as inorganic Hg(II) can be converted to the neurotoxin methylmercury (MeHg), which bioaccumulates and biomagnifies in food webs. Phytoplankton, representing the base of aquatic food webs, can take up Hg(II) and influence MeHg production, but currently little is known about how and to what extent phytoplankton may impact Hg(II) methylation by itself or by methylating bacteria it harbors. This study investigated whether some species of phytoplankton could produce MeHg and how the live or dead phytoplankton cells and excreted algal organic matter (AOM) impact Hg(II) methylation by several known methylators, including iron-reducing bacteria (FeRB), Geobacter anodireducens SD-1 and Geobacter sulfurreducens PCA, and the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans ND132 (or Pseudodesulfovibrio mercurii). Our results indicate that, among the 4 phytoplankton species studied, none were capable of methylating Hg(II). However, the presence of phytoplankton cells (either live or dead) from Chlorella vulgaris (CV) generally inhibited Hg(II) methylation by FeRB but substantially enhanced methylation by SRB D. desulfuricans ND132. Enhanced methylation was attributed in part to CV-excreted AOM, which increased Hg(II) complexation and methylation by ND132 cells. In contrast, inhibition of methylation by FeRB was attributed to these bacteria incapable of competing with phytoplankton for Hg(II) binding and uptake. These observations suggest that phytoplankton could play different roles in affecting Hg(II) methylation by the two groups of anaerobic bacteria, FeRB and SRB, and thus shed additional light on how phytoplankton blooms may modulate MeHg production and bioaccumulation in the aquatic environment.

Recording and Simulating Proton-Related Metabolism in Bacterial Cell Suspensions

Proton release and uptake induced by metabolic activities were measured in non-buffered cell suspensions by means of a pH electrode. Recorded data were used for simulating substrate turnover rates by means of a new freeware app (proton.exe). The program applies Michaelis-Menten or first-order kinetics to the metabolic processes and allows for parametrization of simultaneously ongoing processes. The simulation includes changes of the transmembrane ΔpH, membrane potential and ATP gains, and demonstrates the principles of chemiosmotic energy conservation. In our experiments, the versatile sulfate-reducing bacterium Desulfovibrio desulfuricans CSN (DSM 9104) was used as model organism. We analysed sulfate uptake by proton-sulfate symport, scalar alkalinization by sulfate reduction to sulfide, as well as nitrate and nitrite reduction to ammonia, and electron transport-coupled proton translocation. Two types of experiments were performed: In oxidant pulse experiments, cells were kept under H2, and micromolar amounts of sulfate, nitrate or nitrite were added. For reductant pulse experiments, small amounts of H2-saturated KCl were added to cells incubated under N2 with an excess of one of the above-mentioned electron acceptors. To study electron-transport driven proton translocation, the membrane potential was neutralized by addition of KSCN (100 mM). H+/e– ratios of electron-transport driven proton translocation were calculated by simulation with proton.exe. This method gave lower but more realistic values than logarithmic extrapolation. We could verify the kinetic simulation parameters found with proton.exe using series of increasing additions of the reactants. Our approach allows for studying a broad variety of proton-related metabolic activities at micromolar concentrations and time scales of seconds to minutes.

Mechanisms of Pyrite Formation Promoted by Sulfate-Reducing Bacteria in Pure Culture

Pyrite, or iron disulfide, is the most common sulfide mineral at Earth’s surface and is widespread through the geological record. Because sulfides are mainly produced by sulfate-reducing bacteria (SRB) in modern sedimentary environments, microorganisms are assumed to drive the formation of iron sulfides, in particular pyrite. However, the exact role played by microorganisms in pyrite formation remains unclear and, to date, the precipitation of pyrite in microbial cultures has only rarely been achieved. The present work relies on chemical monitoring, electron microscopies, X-ray diffraction and synchrotron-based spectroscopy to evaluate the formation of iron sulfides by sulfate-reducing bacteria Desulfovibrio desulfuricans as a function of the source of iron, either provided as dissolved Fe2+ or as FeIII-phosphate nanoparticles. Dissolved ferrous iron led to the formation of increasingly crystalline mackinawite (FeS) with time, encrusting bacteria cell walls, hence preventing further sulfate reduction upon day 5 and any evolution of iron sulfides into more stable phases, e.g. pyrite. In contrast, ferric phosphate was transformed into a mixture of large flattened crystals of well crystallized vivianite (Fe3(PO4)2 . 8 H2O) and a biofilm-like thin film of poorly crystallized mackinawite. Although being hosted in the iron sulfide biofilm, most cells were not encrusted. Excess-sulfide delivered by the bacteria and oxidants (such as polysulfides) promoted the evolution of mackinawite into greigite (Fe3S4) and the nucleation of pyrite spherules. These spherules were several hundreds nanometer wide and occurred within the extracellular polymeric substance (EPS) of the biofilm after only 1 month. Altogether, the present study demonstrates that the mineral assemblage induced by the metabolic activity of SRB strongly depends on the source of iron, which has strong implications for the interpretation of the presence of pyrite and vivianite in natural environments.

The reductive glycine pathway allows autotrophic growth of Desulfovibrio desulfuricans

Six CO2 fixation pathways are known to operate in photoautotrophic and chemoautotrophic microorganisms. Here, we describe chemolithoautotrophic growth of the sulphate-reducing bacterium Desulfovibrio desulfuricans (strain G11) with hydrogen and sulphate as energy substrates. Genomic, transcriptomic, proteomic and metabolomic analyses reveal that D. desulfuricans assimilates CO2 via the reductive glycine pathway, a seventh CO2 fixation pathway. In this pathway, CO2 is first reduced to formate, which is reduced and condensed with a second CO2 to generate glycine. Glycine is further reduced in D. desulfuricans by glycine reductase to acetyl-P, and then to acetyl-CoA, which is condensed with another CO2 to form pyruvate. Ammonia is involved in the operation of the pathway, which is reflected in the dependence of the autotrophic growth rate on the ammonia concentration. Our study demonstrates microbial autotrophic growth fully supported by this highly ATP-efficient CO2 fixation pathway.

Inhibition Effectiveness of Laser-Cleaned Nanostructured Aluminum Alloys to Sulfate-reducing Bacteria Based on Superwetting and Ultraslippery Surfaces.

This paper is a continued study on laser cleaning removal of marine microbiofouling from Al alloy surfaces. According to our previous study, it is noted that the antifouling functions of the generated laser-cleaned metallic surfaces must be highlighted. In this work, the inhibition effectiveness of the laser-cleaned Al alloy surfaces was evaluated using a type of vital marine microorganism, sulfate-reducing bacteria (SRB) Desulfovibrio desulfuricans subsp. desulfuricans, in a dynamic bacterial solution. Before the immersion tests, the laser-cleaned surfaces with nanostructures were chemically processed into superhydrophilic, superhydrophobic, and ultraslippery surfaces. SRB attachment behaviors as well as inhibition mechanisms of the three surfaces to the SRB settlement were characterized and revealed. The SRB adhering to the above surfaces presented three different morphologies, i.e., broken, dented, and plump cells. Superhydrophilic surfaces unexpectedly showed a not inferior antibacterial ability. A piercing effect of the nanostructures caused nontoxic mechanical damage to the cell membranes. The antiadhesion property of superhydrophobic solid-air hybrid surfaces was unreliable due to the loss of air bubbles. The morphology of the last surviving SRB cells left on the ultraslippery surfaces was basically plump. The stable repellent function of the surfaces was responsible for the vigorous prevention of the adhesion of the SRB. The research results offer an insight into the antibacterial/antiadhesion properties of the laser-cleaned surfaces and a practical value for the periodic service of marine high-end equipment.

Reduction of perchlorate ions by the sulfate-reducing bacteria Desulfotomaculum sp. and Desulfovibrio desulfuricans

The usage of microorganisms to clean the environment from xenobiotics, in particular chlorine-containing ones, is a promising method of detoxifying the contaminated environment. Sulfate-reducing bacteria Desulfovibrio desulfuricans Ya-11, isolated from Yavoriv Lake, and Desulfotomaculum AR1, isolated from the Lviv sewage treatment system, are able to grow under conditions of environmental contamination by aromatic compounds and chlorine-containing substances. Due to their high redox potential, chlorate and perchlorate ions can be ideal electron acceptors for the metabolism of microorganisms. To test the growth of the tested microorganisms under the influence of perchlorate ions, bacteria were cultured in modified Postgate C medium with ClO4–. Biomass was determined turbidimetrically, the content of sulfate ions and hydrogen sulfide – photoelectrocolorimetrically, the content of perchlorate ions – permanganatometrically. The study of the ability of sulfate-reducing bacteria Desulfotomaculum AR1 and D. desulfuricans Ya-11 to grow in a medium with perchlorate ions as electron acceptors showed the inhibitory effect of ClO4– on sulfate ion reduction by bacteria. Bacteria Desulfotomaculum AR1 and D. desulfuricans Ya-11 are able to grow in environments with aromatic hydrocarbons, in particular toluene. The possibility of the growth of sulfate-reducing bacteria in the presence of toluene as an electron donor and perchlorate ions as an electron acceptor was investigated. The efficiency of perchlorate ion utilization by sulfate-reducing bacteria Desulfotomaculum AR1 and D. desulfuricans Ya-11 was about 90 %. The effect of molybdenum on the reduction of perchlorate ions by Desulfotomaculum AR1 is shown in the paper. Immobilization of bacteria Desulfotomaculum AR1 and D. desulfuricans Ya-11 was carried out in 3% agar and on wood chips. The ability of bacteria, immobilized on these media, to purify the aqueous medium from perchlorate ions was investigated. Reduction of perchlorate ions is more efficiently performed by cells of Desulfotomaculum AR1 and D. desulfuricans Ya-11 bacteria immobilized in agar than on wood chips. Sulfate-reducing bacteria Desulfotomaculum AR1 and D. desulfuricans Ya-11 are able to use perchlorate ions as electron acceptors, purifying the polluted aquatic environment from these pollutants.

Application of mutagenic treatment of active silt for oxidation of cellulose nitrate

The oxidation of native cellulose nitrate (13.38% N) and cellulose nitrate (CN) treated with UV radiation and ozone (UV+ozone) by a biocenosis of microorganisms of active silt (AS) from sewage disposal plants and by a combination of AS with sulfate-reducing bacteria Desulfovibrio desulfuricans BKM B-1388 and microscopic fungi Fusarium solani BKM F-819 was studied. The use of the preliminary treatment significantly increased the degree of decomposition of CN during its subsequent biodegradation by a symbiosis of AS microorganisms with D. desulfuricans and F. solani. The application of the mutagenic treatment of AS with nitrosomethylurea (NMU) allows the biocenosis of AS microorganisms with CN acting as a pollutant to retain high oxidation ability with good sedimentation properties for 65 days of incubation. The degree of decomposition was 24.36%. Substantial parameters were achieved during the incubation period of treated CN (CNtreat) within the first 5 days, which is promising from the point of view of practical use.

Reduction of sulfate, nitrate and nitrite ions by Desulfovibrio sp. under the influence of ferrum (III) citrate

The influence of ferrum (III) citrate added to the cultivation medium, on the reduction of sulfate, nitrate, and nitrite ions by sulfate-reducing bacteria Desulfovibrio desulfuricans IMV K-6, Desulfovibrio sp. Yav-6, and Desulfovibrio sp. Yav-8 isolated from Yavorivske Lake was studied. It was established that ferrum (III) citrate inhibits the biomass accumulation, SO 4 2- reduction, and H 2 S production by the bacteria after addition of 1.74–3.47 mM Na 2 SO 4 ×10 H 2 O and 1.74–10.41 mM FeC 6 H 5 O 7 to the medium, in comparison with the growth and level of the reduction of sulfate ions by bacteria in the medium supplemented with only Na 2 SO 4 ×10 H 2 O. At conditions of the bacteria cultivation in the presence of an equimolar amount (3.47 mM) of Na 2 SO 4 ×10 H 2 O and FeC 6 H 5 O 7 , they reduced 2.5−2.7 times more Fe(ІІІ) than SO 4 2- with Fe 2+ production at a concentration 2.4−2.7 times greater than H 2 S. FeC 6 H 5 O 7 inhibited growth, NO 3 - or NO 2 - reduction and NH 4 + production by the bacteria in the presence of 1.74−3.47 mM NaNO 3 or NaNO 2 and 1.74−10.41 mM FeC 6 H 5 O 7 in the medium, compared to the growth and level of nitrate or nitrite ions reduction in the medium with only NaNO 3 or NaNO 2 . In the medium with the same initial content of 3.47 mM NaNO 3 and 3.47 mM FeC 6 H 5 O 7 , the bacteria reduced 1.4 times more NO 3 - than Fe(ІІІ), with NH 4 + production at concentration 1.1 times higher than that of Fe 2+ . In the medium with 3.47 mM NaNO 2 and 3.47 mM FeC 6 H 5 O 7 , the cells reduced 1.4−1.6 times more Fe(ІІІ) than NO 2 - , with Fe 2+ production at concentra­tion 1.5−1.6 times higher than NH 4 + . Ferrum (III) citrate had more inhibitory effect on the dissimilatory reduction of sulfate by the bacteria than of nitrate and nitrite ions, since the SO 4 2- reduction by the bacteria at its presence in the medium decreased 2.0−4.7 times. The reduction of NO 3 - and NO 2 - decreased only 1.3−1.9 and 1.7−3.1 times, respectively, as compared with their reduction in the media with only Na 2 SO 4 ×10 H 2 O, NaNO 3 or NaNO 2 . Despite the fact that the reduction by cells of 1.74−10.41 mM Fe(III) in the media with Na 2 SO 4 ×10 H 2 O, NaNO 3 or NaNO 2 decreased 1.1−2.1, 1.6−2.7 and 1.1−2.5 times, respectively, compared with its reduction in the medium with only FeC 6 H 5 O 7 . The investigated strains of bacteria were resistant to high concentrations of ferrum (III) citrate and, therefore, can be applied in the technologies of complex environment purification from pollution with ferrum, sulfur, and nitrogen compounds.

Upconversion of Cellulosic Waste Into a Potential "Drop in Fuel" via Novel Catalyst Generated Using Desulfovibrio desulfuricans and a Consortium of Acidophilic Sulfidogens.

Biogas-energy is marginally profitable against the “parasitic” energy demands of processing biomass. Biogas involves microbial fermentation of feedstock hydrolyzate generated enzymatically or thermochemically. The latter also produces 5-hydroxymethyl furfural (5-HMF) which can be catalytically upgraded to 2, 5-dimethyl furan (DMF), a “drop in fuel.” An integrated process is proposed with side-stream upgrading into DMF to mitigate the “parasitic” energy demand. 5-HMF was upgraded using bacterially-supported Pd/Ru catalysts. Purpose-growth of bacteria adds additional process costs; Pd/Ru catalysts biofabricated using the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans were compared to those generated from a waste consortium of acidophilic sulfidogens (CAS). Methyl tetrahydrofuran (MTHF) was used as the extraction-reaction solvent to compare the use of bio-metallic Pd/Ru catalysts to upgrade 5-HMF to DMF from starch and cellulose hydrolyzates. MTHF extracted up to 65% of the 5-HMF, delivering solutions, respectively, containing 8.8 and 2.2 g 5-HMF/L MTHF. Commercial 5% (wt/wt) Ru-carbon catalyst upgraded 5-HMF from pure solution but it was ineffective against the hydrolyzates. Both types of bacterial catalyst (5wt%Pd/3-5wt% Ru) achieved this, bio-Pd/Ru on the CAS delivering the highest conversion yields. The yield of 5-HMF from starch-cellulose thermal treatment to 2,5 DMF was 224 and 127 g DMF/kg extracted 5-HMF, respectively, for CAS and D. desulfuricans catalysts, which would provide additional energy of 2.1 and 1.2 kWh/kg extracted 5-HMF. The CAS comprised a mixed population with three patterns of metallic nanoparticle (NP) deposition. Types I and II showed cell surface-localization of the Pd/Ru while type III localized NPs throughout the cell surface and cytoplasm. No metallic patterning in the NPs was shown via elemental mapping using energy dispersive X-ray microanalysis but co-localization with sulfur was observed. Analysis of the cell surfaces of the bulk populations by X-ray photoelectron spectroscopy confirmed the higher S content of the CAS bacteria as compared to D. desulfuricans and also the presence of Pd-S as well as Ru-S compounds and hence a mixed deposit of PdS, Pd(0), and Ru in the form of various +3, +4, and +6 oxidation states. The results are discussed in the context of recently-reported controlled palladium sulfide ensembles for an improved hydrogenation catalyst.

Mercury Uptake by Desulfovibrio desulfuricans ND132: Passive or Active?

Recent studies have identified HgcAB proteins as being responsible for mercury [Hg(II)] methylation by certain anaerobic microorganisms. However, it remains controversial whether microbes take up Hg(II) passively or actively. Here, we examine the dynamics of concurrent Hg(II) adsorption, uptake, and methylation by both viable and inactivated cells (heat-killed or starved) or spheroplasts of the sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 in laboratory incubations. We show that, without addition of thiols, >60% of the added Hg(II) (25 nM) was taken up passively in 48 h by live and inactivated cells and also by cells treated with the proton gradient uncoupler, carbonylcyanide-3-chlorophenylhydrazone (CCCP). Inactivation abolished Hg(II) methylation, but the cells continued taking up Hg(II), likely through competitive binding or ligand exchange of Hg(II) by intracellular proteins or thiol-containing cellular components. Similarly, treatment with CCCP impaired the ability of spheroplasts to methylate Hg(II) but did not stop Hg(II) uptake. Spheroplasts showed a greater capacity to adsorb Hg(II) than whole cells, and the level of cytoplasmic membrane-bound Hg(II) correlated well with MeHg production, as Hg(II) methylation is associated with cytoplasmic HgcAB. Our results indicate that active metabolism is not required for cellular Hg(II) uptake, thereby providing an improved understanding of Hg(II) bioavailability for methylation.

Mercury Sorption and Desorption on Organo-Mineral Particulates as a Source for Microbial Methylation.

In natural freshwater and sediments, mercuric mercury (Hg(II)) is largely associated with particulate minerals and organics, but it remains unclear under what conditions particulates may become a sink or a source for Hg(II) and whether the particulate-bound Hg(II) is bioavailable for microbial uptake and methylation. In this study, we investigated Hg(II) sorption-desorption characteristics on three organo-coated hematite particulates and a Hg-contaminated natural sediment and evaluated the potential of particulate-bound Hg(II) for microbial methylation. Mercury rapidly sorbed onto particulates, especially the cysteine-coated hematite and sediment, with little desorption observed (0.1-4%). However, the presence of Hg-binding ligands, such as low-molecular-weight thiols and humic acids, resulted in up to 60% of Hg(II) desorption from the Hg-laden hematite particulates but <6% from the sediment. Importantly, the particulate-bound Hg(II) was bioavailable for uptake and methylation by a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under anaerobic incubations, and the methylation rate was 4-10 times higher than the desorption rate of Hg(II). These observations suggest direct contacts and interactions between bacterial cells and the particulate-bound Hg(II), resulting in rapid exchange or uptake of Hg(II) by the bacteria. The results highlight the importance of Hg(II) partitioning at particulate-water interfaces and the role of particulates as a significant source of Hg(II) for methylation in the environment.

Evaluation of denitration of nitrocellulose by microbiological treatment for industrial waste effluents using calorimetry analysis

The problem of utilization of the compounds present in the effluents of the production of cellulose nitrates (NC) is very important and complicated, and its decision is inextricably related to the environment. The process of heat release in the samples of nitrocellulose subjected to biological processing of different types was studied. Biological processing was conducted by incubation with sulfate-reducing bacteria Desulfovibrio desulfuricans BКMB-1388, microscopic fungi Fusarium solani BKM F-819, and their mixed culture. The studies were carried out on the native NC (13.38% nitrogen) and the NC processed (NCproc) using ultraviolet radiation and ozone (UV + ozone). It has been shown that the pretreatment of the NC by UV + ozone significantly increases the degree of decomposition of the NC during its subsequent biodegradation assisted by symbiotic microorganisms of D. desulfuricans and F. solani. A substantial result was achieved on the fifth day of NCproc incubation, which is promising from the viewpoint of practical applications.

Bio-Reduction of Graphene Oxide Using Sulfate-Reducing Bacteria and Its Implication on Anti-Biocorrosion.

In this paper, we developed an environmental friendly, cost effective, simple and green approach to reduce graphene oxide (GO) by a sulfate-reducing bacterium Desulfovibrio desulfuricans. The D. desulfuricans reduces exfoliated GO to reduced graphene oxide (rGO) at 25 °C in an aqueous solution without any toxic and environmentally harmful reducing agents. The rGO was characterized with X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscope, X-ray Photoelectron Spectroscopy and Raman Spectroscopy. The analysis results showed that rGO had excellent properties and multi-layer graphene sheets structure. Furthermore, we demonstrated that D. desulfuricans, one of the primary bacteria responsible for the biocorrosion of various metals, might reduce GO to rGO on the surface of copper and prevented the corrosion of copper, which confirmed that electrophoretic deposition of GO on the surface of metals had great potential on the anti-biocorrosion applications.

Nanomolar Copper Enhances Mercury Methylation by Desulfovibrio desulfuricans ND132

Methylmercury (MeHg) is produced by certain anaerobic microorganisms, such as the sulfate-reducing bacterium Desulfovibrio desulfuricans ND132, but environmental factors affecting inorganic mercury [Hg(II)] uptake and methylation remain unclear. We report that the presence of a small amount of copper ions [Cu(II), <100 nM] enhances Hg(II) uptake and methylation by washed cells of ND132, while Hg(II) methylation is inhibited at higher Cu(II) concentrations because of the toxicity of copper to the microorganism. The enhancement or inhibitory effect of Cu(II) is dependent on both time and concentration. The presence of nanomolar concentrations of Cu(II) facilitates rapid uptake of Hg(II) (within minutes) and doubles MeHg production within a 24 h period, but micromolar concentrations of Cu(II) completely inhibit Hg(II) methylation. Metal ions such as zinc [Zn(II)] and nickel [Ni(II)] also inhibit but do not enhance Hg(II) methylation under the same experimental conditions. These observations suggest a synergi...

Nitrocellulose Degradation by the Fungus Fusarium solani

The degradation of native and pretreated nitrocellulose (NC) by the microscopic fungus Fusarium solani VKM F-819 and a mixed culture of the fungus with a sulfate-reducing bacterium Desulfovibrio desulfuricans VKM B-1388 has been studied. It has been shown that NC pretreatment with UV radiation and ozone promoted its subsequent biodegradation. The degradation of the thus treated NC by a mixed culture of F. solani and D. desulfuricans was the most effective as compared to all other treatment options. The NC nitrogen content decreased from 13.38 to 10.03%; the number average (Mn) and weight average (Mw) molecular masses decreased by three and two times, respectively. These magnitudes were achieved after 5 days of incubation of the pretreated NC. The obtained data can be used to further develop NC degradation technology.

Coordinated response of the Desulfovibrio desulfuricans 27774 transcriptome to nitrate, nitrite and nitric oxide

The sulfate reducing bacterium Desulfovibrio desulfuricans inhabits both the human gut and external environments. It can reduce nitrate and nitrite as alternative electron acceptors to sulfate to support growth. Like other sulphate reducing bacteria, it can also protect itself against nitrosative stress caused by NO generated when nitrite accumulates. By combining in vitro experiments with bioinformatic and RNA-seq data, metabolic responses to nitrate or NO and how nitrate and nitrite reduction are coordinated with the response to nitrosative stress were revealed. Although nitrate and nitrite reduction are tightly regulated in response to substrate availability, the global responses to nitrate or NO were largely regulated independently. Multiple NADH dehydrogenases, transcription factors of unknown function and genes for iron uptake were differentially expressed in response to electron acceptor availability or nitrosative stress. Amongst many fascinating problems for future research, the data revealed a YtfE orthologue, Ddes_1165, that is implicated in the repair of nitrosative damage. The combined data suggest that three transcription factors coordinate this regulation in which NrfS-NrfR coordinates nitrate and nitrite reduction to minimize toxicity due to nitrite accumulation, HcpR1 serves a global role in regulating the response to nitrate, and HcpR2 regulates the response to nitrosative stress.

Biological removal of gaseous sulfur dioxide through the reduction to hydrogen sulfide by means of Desulfovibrio desulfuricans

The biological removal of gaseous sulfur dioxide using the sulfate reducing bacteria Desulfovibrio desulfuricans is studied. Laboratory-scale bioreactors were designed to generate sulfur dioxide in them through a chemical reaction. To evaluate the biological reduction, three kinetics (in triplicate) were taken in batch mode with loads of 15, 20 and 25 mmol of SO2 generated in the gas phase per liter of culture medium in the liquid phase. Lactate was used as substrate (electron donor) and carbon source. The experimental results showed a 100% SO2 reduction for all the evaluated loads. The tests lasted 24, 72 and 192 h, with lower, intermediate and higher loads, respectively. The total sulfide (S2−) produced varied between 75 and 126 mg for the tests with lower and higher load, respectively. These amounts were composed of a fraction in the aqueous phase (287 and 533 mg of S2−/L) and another in the gas phase (0.9 × 108 and 2.7 × 108 μg H2S/m3). The mass ratio between product formation (sulfide) and electron donor consumption (expressed as COD) ranged from 81% to 90% of the theoretical value (0.67 mg of sulfide produced per mg of COD consumed).

Contrasting Effects of Dissolved Organic Matter on Mercury Methylation by Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132.

Natural dissolved organic matter (DOM) affects mercury (Hg) redox reactions and anaerobic microbial methylation in the environment. Several studies have shown that DOM can enhance Hg methylation, especially under sulfidic conditions, whereas others show that DOM inhibits Hg methylation due to strong Hg-DOM complexation. In this study, we investigated and compared the effects of DOM on Hg methylation by an iron-reducing bacterium Geobacter sulfurreducens PCA and a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under nonsulfidic conditions. The methylation experiment was performed with washed cells either in the absence or presence of DOM or glutathione, both of which form strong complexes with Hg via thiol-functional groups. DOM was found to greatly inhibit Hg methylation by G. Sulfurreducens PCA but enhance Hg methylation by D. desulfuricans ND132 cells with increasing DOM concentration. These strain-dependent opposing effects of DOM were also observed with glutathione, suggesting that thiols in DOM likely played an essential role in affecting microbial Hg uptake and methylation. Additionally, DOM and glutathione greatly decreased Hg sorption by G. sulfurreducens PCA but showed little effect on D. desulfuricans ND132 cells, demonstrating that ND132 has a higher affinity to sorb or take up Hg than the PCA strain. These observations indicate that DOM effects on Hg methylation are bacterial strain specific, depend on the DOM:Hg ratio or site-specific conditions, and may thus offer new insights into the role of DOM in methylmercury production in the environment.