Mixed Culture Of Sulfate-reducing Bacteria Research Articles

Corrosion behaviour of X60 steel in the presence of sulphate-reducing bacteria (SRB) and iron-reducing bacteria (IRB) in seawater

ABSTRACT In this study, the corrosion behavior of X60 was investigated in the presence of a mixed culture of sulfate-reducing bacteria (SRB) and iron-reducing bacteria (IRB) via weight loss, electrochemical impedance spectroscopy (EIS), and Tafel polarization techniques. Moreover, field emission scanning electron microscope (FESEM) images and X-ray diffraction spectrometry (XRD) were used to study the morphological changes of the surface of X60 and the composition of corrosion products after exposing X60 to the abiotic and biotic systems. EIS result confirmed the occurrence of microbial corrosion in the presence of SRB and IRB. In the exposed coupon to the mixture of bacteria, the result illustrated that the existence of IRB promoted the SRB growth, so corrosion rate increased compared to the exposed coupon to SRB and IRB, respectively. The mixture of SRB and IRB showed a synergistic effect and enhanced the pitting corrosion on the surface of X60.

Bioremoval of arsenic and antimony from wastewater by a mixed culture of sulfate-reducing bacteria using lactate and ethanol as carbon sources

We investigated the remediation of wastewater containing As and Sb through the application of a mixed culture of sulfate-reducing bacteria (SRB). The effect of Fe(II) and different carbon sources on the removal of As and Sb was evaluated. The wastewater initially contained 5 mg L−1 of both As(V) and Sb(V), and the treatment was conducted over a 12-d period. The produced precipitates were characterized by TEM and XRD to elucidate the metalloid removal mechanism. In the absence of Fe(II), Sb was efficiently removed (97.6% and 97.8% with lactate and ethanol as carbon sources, respectively, hereinafter the same), whereas only a relatively small fraction (27.8% and 26.4%) of As was removed. The addition of 200 mg L−1 Fe(II) greatly improved the removal of As (78% and 98.2%) and further increased the removal of Sb (98.8% and 99.4%). We hypothesized that As was removed through sorption/co-precipitation by FeS instead of the formation of As2S3. The use of ethanol as a carbon source generated a relatively lower yield of sulfide compared to the use of lactate, but it resulted in a higher removal of As and Sb. This may be attributed to the low production of sulfide, which possibly resulted in the slow precipitation of FeS that enhanced the sorption/co-precipitation of ions. This work demonstrates the high application potential of ethanol as a carbon source and the addition of Fe(II) in the bioremoval of As and Sb from wastewater by SRB.

Effect of copper upon the actions of sulphate-reducing bacteria isolated from soil contaminated by crude oil and heavy metals / Wpływ miedzi na aktywność bakterii redukujących siarczany wyizolowanych z gleby zanieczyszczonej ropą naftową i metalami ciężkimi

Abstract In the present study, copper tolerance by a mixed culture of sulphate-reducing bacteria (SRB) were evaluated. These sulphidogenic microbial communities were isolated from soils polluted by crude oil, oil-derived products and heavy metals (from selected areas of crude oil mines in south-eastern Poland). Copper tolerance of SRB was tested in modified Postgate C medium with ethanol and lactate as the sole carbon source and copper chloride at concentrations ranging from 0 to 1500 mg/l. Bacterial growth and sulphate reduction were possible between 100 and 1500 mg/l of initial copper concentration. Active sulphate reduction - maximum of 53% was observed in the cultures. Molecular analysis indicated not only the presence of SRB but also other microorganisms that are capable of living in environments contaminated by heavy metals. The high environmental sulphide concentrations produced by SRB lead to the precipitation of any biogenic mineral phases such as metal sulphides. As a result, soluble metal ion concentrations in the microenvironment of SRB are, therefore, extremely low. This process allows SRB to grow in environments containing high levels of toxic metals. Studies on SRB tolerance to heavy metals are extremely important because of the possibility of using this group of microorganisms for the bioremediation and microbial revitalisation of areas contaminated by heavy metals.

Anodic potential on dual-chambered microbial fuel cell with sulphate reducing bacteria biofilm

Dual chamber microbial fuel cell reactors were inoculated with a mixed culture of sulfate-reducing bacteria with anode potential being the controlling parameter. A negative poised anode potential enhanced the performance of this fuel cell while a positive poised anode potential had adverse effects on cell performance. Negative anodic potential affects the biofilm characteristics, as evidenced by electrochemical analysis. Microbial community was changed accordingly.

Control of dual-chambered microbial fuel cell by anodic potential: Implications with sulfate reducing bacteria

Five dual chamber microbial fuel cell reactors were inoculated with a mixed culture of sulfate-reducing bacteria and fed with artificial wastewater containing lactate and sulfate. A negative poised anode potential enhanced the performance of this fuel cell while a positive poised anode potential or no anode potential had no effect on performance. The effect of this anode potential promoted microbial colonization on the anode surface (biofilm) thereby presenting an effective and successful way for the start-up of a sulfate reducing bacterial microbial fuel cell.

Microbial removal of uranyl by sulfate reducing bacteria in the presence of Fe (III) (hydr)oxides

Microbiological reduction of uranyl by sulfate reducing bacteria (SRB) has been proposed as a promising method for removal of radionuclide from groundwater. In this study, we examined the effect of two naturally occurring Fe(III) (hydr)oxides, hematite and goethite, on the bioreduction of U(VI) by a mixed culture of SRB via laboratory batch experiments. The biogenic precipitate from U(VI) bioreduction was determined using X-ray absorption near edge structure (XANES) analysis, showing a typical feature of uraninite (UO 2). In the presence of either hematite or goethite-containing Fe(III) ranging from 10 to 30 mM, the reduction of U(VI) was retarded by both minerals and the retardatory effect was enhanced with increasing amount of Fe(III) (hydr)oxide. When exposed to a mixture of hematite and goethite with the total Fe(III) kept constant at 20 mM, the retardatory effect on U(VI) reduction by the minerals were directly correlated with the fraction of hematite present. A slow increase in U(VI) concentration was also found in all Fe(III) (hydr)oxide treatments after 10–13 days, accompanied by the release of Fe(II) into the solution. The presence of Fe(III) (hydr)oxide can cause the eventual incomplete bioreduction of U(VI). However, it was not the case for the control without minerals. When mixing biogenic uraninite with hematite or goethite without SRB, Fe(II) was also detected in the solution. These findings suggest that the U(VI) remobilization after 10～13 days may be due to reoxidation of the uraninite by the solid-phase Fe(III) (hydr)oxide.

Bioremoval of arsenic species from contaminated waters by sulphate-reducing bacteria

A mixed culture of sulphate-reducing bacteria was used to study the bioremoval of arsenic species (As(III) or As(V)) from groundwater. During growth of a mixed SRB culture adapted to 0.1 mg/L arsenic species through repeated sub-culturing, 1 mg/L of either As(III) or As(V) was reduced to 0.3 and 0.13 mg/L respectively. Sorption experiments on the precipitate produced by batch cultured sulphate-reducing bacteria (SRB-PP) indicated a removal of about 77 and 55% of As(V) and As(III) respectively under the following conditions: pH 6.9; biomass (2 g/L); 24 h contact time; initial arsenic concentration, 1 mg/L of either species. These results were compared with synthetic iron sulphide as adsorbent. The adsorption data were fitted to Langmuir and Freundlich isotherms. Energy dispersive X-ray analysis showed the SRB-PP contained elements such as sulphur, iron, calcium and phosphorus. Biosorption studies indicated that SRB cell pellets removed about 6.6% of the As(III) and 10.5% of the As(V) from water containing an initial concentration of 1 mg/L of either arsenic species after 24 h contact.

The treatment of textile wastewater including chromium(VI) and reactive dye by sulfate-reducing bacterial enrichment

Sulfate-reducing bacteria (SRB) that could grow on modified Postgate C medium (PC) containing chromium(VI) were isolated from industrial wastewaters and their chromium(VI) reduction capacities were investigated as a function of changes in the initial pH values, chromium, sulfate, NaCl and reactive dye concentrations. The optimum pH value at 50 mg l −1 initial chromium(VI) concentration was determined to be 8. Chromium(VI) reduction by SRB was investigated at 22.7–98.4 mg l −1 initial chromium(VI) concentrations. At the end of the experiments, the mixed cultures of SRB were found to reduce within 2–6 days more than 99% of the initial chromium(VI) levels, which ranged from 22.7 to 74.9 mg l −1. The effects of the initial 0–9.0 g l −1 concentrations of disodium sulfate and 0–6% (w/v) concentrations of NaCI to chromium reduction showed that the lowest concentrations of sulfate and NaCI were the best for chromium reduction in the PC medium including 50 mg l −1 chromium(VI). Chromium(VI) reduction in 50 mg l −1 and 25–100 mg l −1 Remazol Blue, Reactive Black B or Reactive Red RB containing media were also investigated. In the experiments, 25–30% of the initial dye concentrations and 95% of the chromium(VI) was removed from the medium at the end of 72-h and 24-h incubation periods, respectively.

Formation of Covellite (CuS) Under Biological Sulfate-Reducing Conditions

Sulfate-reducing bacteria (SRB) play a major role in the precipitation of metal sulfides in the environment. In this work, biogenic copper sulfide formation was examined in cultures of SRB and compared to chemically initiated Cu sulfide precipitation as a reference system. Mixed cultures of SRB were incubated at 22, 45, and 60°C in nutrient solutions that contained copper sulfate. Abiotic reference samples were produced by reacting uninoculated liquid media with Na2S solutions under otherwise identical conditions. Precipitates were collected anaerobically by centrifugation, frozen in liquid N2, and freeze-dried, followed by analysis using X-ray diffraction (XRD), X-ray fluorescence, and scanning electron microscopy. Covellite (CuS) was the only mineral found in the precipitates. Covellite was less crystalline in the biogenic precipitates than in the abiotic samples based on XRD peak widths and peak to background ratios. Poor crystallinity may be the result of slower precipitation rates in bacterial cultures as compared to the abiotic reference systems. Furthermore, bacterial cells may inhibit the nucleation steps that lead to crystal formation. Incubation at elevated temperatures improved the crystallinity of the biotic specimens.

Zinc precipitation by heavy-metal tolerant sulfate-reducing bacteria enriched on phosphogypsum as a sulfate source

In the present study, heavy-metal tolerance and precipitation by a mixed culture of sulfate-reducing bacteria (SRB) were evaluated. These bacteria have been enriched during a previous study from a sewage sludge using phosphogypsum as sulfate source. Taking into account that both sulfate and zinc are naturally occurring in phosphogypsum, zinc tolerance of SRB was tested in synthetic media containing 20 mM sulfate and zinc chloride at concentrations ranging from 0 to 200 mg L −1. Zinc tolerance was determined by bacterial growth susceptibility and zinc removal monitoring. Bacterial growth and sulfate reduction were possible between 10 and 150 mg L −1 of initial zinc concentration. Zinc concentrations more than 150 mg L −1 were lethal to SRB. Zinc was removed effectively by SRB to less than 5% from medium containing 150 mg L −1 initial zinc concentrations or less. Energy-dispersive X-ray analysis showed that precipitation of zinc occurred in the form of sulfide. The results presented in this paper have shown that this mixed culture might be of use for bioremediation of sulfate and heavy-metals containing wastewaters.

Identification of population dynamics in sulfate-reducing consortia on exposure to sulfate

The microbial population structure and function of a mixed culture of sulfate-reducing bacteria (SRB) maintained in anaerobic continuous bioreactors were tracked before and after a major perturbation, which involved the addition of sulfate to the influent of a bioreactor when operated at steady state at 35 °C, pH 7.8 and a 2.5 day residence time with feed stream containing 10 and 15 kg m −3 sulfate as terminal electron acceptor and 19.6 and 29.4 kg m −3 ethanol as carbon source and electron donor, respectively. The population structure determined by fluorescence in situ hybridization (FISH), by using 16S rRNA-targeted oligonucleotide probes, was linked to the functional performance of the SRB in the reactor. Hybridization analysis using these 16S rRNA-targeted oligonucleotide probes revealed that a high concentration of sulfate was toxic for Desulfobacterium and Desulfobulbus. On the other hand, the Desulfococcus group was found to be the most dominant group of SRB in the feed stream containing 15 kg m −3 sulfate as terminal electron acceptor and 29.4 kg m −3 ethanol as carbon source and electron donor.

Microbiologically assisted stress corrosion cracking of carbon steel in mixed and pure cultures of sulfate reducing bacteria

The role of microbiological environments containing pure and mixed cultures of sulfate-reducing bacteria in stress corrosion cracking of carbon steel in biotic and abiotic environments was investigated. Carbon steel specimens were subjected to slow strain rate testing in a synthetic seawater environment (3.5% sodium chloride solution), with and without the microbiological cultures. Specimens tested in biotic (microbiological) conditions showed a considerable loss of ductility, as compared to those tested in abiotic conditions. Fractography of the specimens tested in abiotic solutions suggested features of only ductile failure (dimples), whereas those tested in biotic conditions had additional features of brittle cracking. Results also suggested the role of sulfate-reducing bacteria in promoting hydrogen-assisted cracking.

Exposure to sulfide causes populations shifts in sulfate-reducing consortia

The shift in the community structure of a mixed culture of sulfate-reducing bacteria (SRB) at 0.5, 0.75, 1, and 1.5 kg m −3 sulfide loadings was investigated in an anaerobic continuous bioreactor used for treatment of sulfate-containing wastewater by fluorescence in situ hybridization (FISH), using SRB species-specific and group-specific 16S rRNA-targeting probes. Hybridization analysis using these 16S rRNA-targeted oligonucleotide probes revealed that sulfide was toxic for Desulfonema, Desulfobulbus spp. and the Desulfobacteriaceae group, although it was not toxic for Desulfobacter, Desulfotomaculum, Desulfobacterium spp. or the Desulfovibrionaceae group. On the other hand, only a high concentration of sulfide of 1.5 kg m −3 was found to be toxic for the Desulfococcus group in the bioreactor. When the sulfide in the feed was 1.00 kg m −3 the sulfate-reducing capacity of the system decreased, and this decrease was more pronounced when the inlet sulfide was further increased to 1.5 kg m −3.

Sulfate reduction from phosphogypsum using a mixed culture of sulfate-reducing bacteria

Abstract Phosphogypsum (CaSO4), a primary by-product of phosphoric acid production, is accumulated in large stockpiles and occupies vast areas of land. It poses a severe threat to the quality of water and land in countries producing phosphoric acid. In this study, the potential of sulfate-reducing bacteria for biodegradation of this sulfur-rich industrial solid waste was assessed. The effect of phosphogypsum concentration, carbon and nitrogen sources, temperature, pH and stirring on the growth of sulfate-reducing bacteria was investigated. Growth of sulfate-reducing bacteria was monitored by measuring sulfide production. Phosphogypsum was shown to be a good source of sulfate, albeit that the addition of organic carbon was necessary for bacterial growth. Biogenic sulfide production occurred with phosphogypsum up to a concentration of 40 g L−1, above which no growth of sulfate-reducing bacteria was observed. Optimal growth was obtained at 10 g L−1 phosphogypsum. Both the gas mixture H2/CO2 and lactate supported high amounts of H2S formation (19 and 11 mM, respectively). The best source of nitrogen for sulfate-reducing bacteria was yeast extract, followed by ammonium chloride. The presence of nitrate had an inhibitory effect on the process of sulfate reduction. Stirring the culture at 150 rpm slightly stimulated H2S formation, probably by improving sulfate solubility.

Cadmium accumulation and DNA homology with metal resistance genes in sulfate-reducing bacteria.

Cadmium resistance (0.1 to 1.0 mM) was studied in four pure and one mixed culture of sulfate-reducing bacteria (SRB). The growth of the bacteria was monitored with respect to carbon source (lactate) oxidation and sulfate reduction in the presence of various concentrations of cadmium chloride. Two strains Desulfovibrio desulfuricans DSM 1926 and Desulfococcus multivorans DSM 2059 showed the highest resistance to cadmium (0.5 mM). Transmission electron microscopy of the two strains showed intracellular and periplasmic accumulation of cadmium. Dot blot DNA hybridization using the probes for the smtAB, cadAC, and cadD genes indicated the presence of similar genetic determinants of heavy metal resistance in the SRB tested. DNA sequencing of the amplified DNA showed strong nucleotide homology in all the SRB strains with the known smtAB genes encoding synechococcal metallothioneins. Protein homology with the known heavy metal-translocating ATPases was also detected in the cloned amplified DNA of Desulfomicrobium norvegicum I1 and Desulfovibrio desulfuricans DSM 1926, suggesting the presence of multiple genetic mechanisms of metal resistance in the two strains.

Acute toxicity of heavy metals to acetate‐utilizing mixed cultures of sulfate‐reducing bacteria: EC100 and EC50

Acid mine drainage from abandoned mines and acid mine pit lakes is an important environmental concern and usually contains appreciable concentrations of heavy metals. Because sulfate-reducing bacteria (SRB) are involved in the treatment of acid mine drainage, knowledge of acute metal toxicity levels for SRB is essential for the proper functioning of the treatment system for acid mine drainage. Quantification of heavy metal toxicity to mixed cultures of SRB is complicated by the confounding effects of metal hydroxide and sulfide precipitation, biosorption, and complexation with the constituents of the reaction matrix. The objective of this paper was to demonstrate that measurements of dissolved metal concentrations could be used to determine the toxicity parameters for mixed cultures of sulfate-reducing bacteria. The effective concentration, 100% (EC100), the lowest initial dissolved metal concentrations at which no sulfate reduction is observed, and the effective concentration, 50% (EC50), the initial dissolved metal concentrations resulting in a 50% decrease in sulfate reduction, for copper and zinc were determined in the present study by means of nondestructive, rapid physical and chemical analytical techniques. The reaction medium used in the experiments was designed specifically (in terms of pH and chemical composition) to provide the nutrients necessary for the sulfidogenic activity of the SRB and to preclude chemical precipitation of the metals under investigation. The toxicity-mitigating effects of biosorption of dissolved metals were also quantified. Anaerobic Hungate tubes were set up (at least in triplicate) and monitored for sulfate-reduction activity. The onset of SRB activity was detected by the blackening of the reaction mixture because of formation of insoluble ferrous sulfide. The EC100 values were found to be 12 mg/L for copper and 20 mg/L for zinc. The dissolved metal concentration measurements were effective as the indicators of the effect of the heavy metals at concentrations below EC100. The 7-d EC50 values obtained from the difference between the dissolved metal concentrations for the control tubes (tubes not containing copper or zinc) and tubes containing metals were found to be 10.5 mg/L for copper and 16.5 mg/L for zinc. Measurements of the turbidity and pH, bacterial population estimations by means of a most-probable number technique, and metal recovery in the sulfide precipitate were found to have only a limited applicability in these determinations.

Treatment of acid lignite mine flooding water by means of microbial sulfate reduction

During and after mining activities acidic waters containing high amounts of heavy metals and sulfate often occur. In addition to precipitation processes, water purification is also possible with the help of sulfate-reducing bacteria (SRB). A mixed culture of SRB was adapted to methanol as a cheap carbon source. In order to receive high sulfate-reduction rates immobilization on porous materials proved to be advantageous. Continuous laboratory experiments based on immobilized SRB were carried out with original water from a lignite mining site reaching sulfate-reducing rates up to 132 mg SO 4 2−/(l h). Based on these results a process for the treatment of such waters was designed. Heavy metals are removed by recycling sulfide containing effluent, excess sulfide can be oxidized to elemental sulfur by addition of hydrogen peroxide. The plant with a 3.9 m 3 bioreactor with immobilized SRB was constructed at the mine site. This pilot plant was operated successfully for some months. The removal of heavy metals was close to 100%, the pH of the acidic water increased from 3.0 to 6.9. The sulfate-reducing rate again reached 134 mg SO 4 2−/(l h). The production of sulfur from the excess sulfide is possible.

Attachment and Growth of Sulphate-Reducing Bacteria on Different Support Materials

Attachment and growth of sulphate-reducing bacteria on different surfaces was studied. A mixed culture of sulphate-reducing bacteria was grown autotrophically on a CO2/H2 mixture in a defined medium in the presence of support materials: polyurethane foam, lava rock and Ringlace®, and encapsulated in alginate beads. Over a period of fourteen days, the quantities of biomass attached to the support particles and in suspension were determined by measuring the total kjeldahl nitrogen (TKN) content of the respective attached and suspended portions. For the foam and the alginate beads, 73% and 84%, respectively, of the total biomass was attached to the support material at the end of the fourteen days. For the Ringlace® and lava rock much lesser amounts of biomass were attached to the supports. Scanning electron micrographs showed that the cells adhered to the surface of the foam and formed aggregates in the porous cavities of the foam. These aggregates appeared to be attached to the foam surface via strands of extrapolymeric substance. The cells encapsulated in the alginate beads grew preferentially in the centre of the bead. Some cells were seen growing in pockets on the surface of the lava rock particles. A few cells were very sparsely distributed on the surface of the Ringlace®.

Ethanol utilization by sulfate-reducing bacteria: An experimental and modeling study

A mixed culture of sulfate-reducing bacteria containing the species Desulfovibrio desulfuricans was used to study sulfate-reduction stoichiometry and kinetics using ethanol as the carbon source. Growth yield was lower, and kinetics were slower, for ethanol compared to lactate. Ethanol was converted into acetate and no significant carbon dioxide production was observed. A mathematical model for growth of sulfate-reducing bacteria on ethanol was developed, and simulations of the growth experiments on ethanol were carried out using the model. The pH variation due to sulfate reduction, and hydrogen sulfide production and removal by nitrogen sparging, were examined. The modeling study is distinct from earlier models for systems using sulfate-reducing bacteria in that it considers growth on ethanol, and analyzes pH variations due to the product-formation reactions.

Physicochemical and Biogeochemical Stabilization of Uranium in a Low Level Radioactive Waste Disposal Cell

An on-site disposal cell is being evaluated for the long-term disposition of materials generated by CERCLA (Comprehensive Environmental Response Compensation and Liability Act of 1980) remediation activities on the U.S. Department of Energy Oak Ridge Reservation (ORR), Oak Ridge, Tennessee. The leaching characteristics of the expected waste materials indicates that uranium concentrations in the leachate could exceed 30 mg/L. Addition of a geochemical barrier to the disposal cell design, or the application of chemical amendments to the waste materials, have been suggested as methods to reduce uranium levels in leachate leaving the disposal cell. Three promising approaches were identified: a) stabilization of mobile uranium by sulfate-reducing bacteria; b) stabilization of uranium as low solubility oxides by hydrated lime addition; and c) sorption of mobile uranium by a peat moss-based geochemical barrier in the disposal cell. Bench scale tests were conducted to evaluate the relative effectiveness of these three approaches. The results suggest that: a) a peat moss-based barrier would be effective in removing uranium initially, but long-term exposure to an alkaline leachate would result in the resolubilization and transport of uranium previously sorbed onto the peat moss; b) even large applications of hydrated lime to uranium-contaminated soils would not stabilize uranium in a high alkalinity, high pH environment; and c) mixed cultures of sulfate-reducing bacteria will greatly attenuate uranium levels (even in alkaline solutions) by precipitating it in the reduced form as UO 2 . Consequently, a geochemical barrier containing sulfate-reducing bacteria should be more effective than one using peat moss or hydrated lime.