Activity Of Sulfate-reducing Bacteria Research Articles

Effect of CO2 and salinity on microbial hydrogen sulphide generation in hydrocarbon reservoirs

This work investigates the effects of CO2 and salinity on the biosouring process in hydrocarbon reservoirs that is applicable in carbonated low salinity or smart water injection projects. Biosouring refers to the generation of hydrogen sulphide gas in oil reservoirs due to the activity of sulphate reducing bacteria (SRB). The influence of key parameters including pH (that is affected by CO2 concentration), temperature, and salinity on the microbial activity of SRB is studied using a Buckley-Leverett based flow model linked to PHREEQC geochemistry software. Simulation results are validated against some experimental data taken from the literature. The simulations are performed at varying pH (6.0–7.0), temperature (40–100 °F), and salinity (0.5–0.8 meq/ml) of NaCl to assess their effects on the souring process. Additionally, two models are developed applying the response surface method to relate the concentration of hydrogen sulphide and souring onset to pH, temperature, and salinity. The results suggest that the souring onset delays when the reservoir pH decreases (pH ≤ 6.0) and injection temperature and salinity increase. Moreover, higher values of pH result in an early onset if the temperature is kept low (40–60 °F). The findings also indicate that temperature and salinity affect the H2S concentration. The highest H2S concentrations are observed when the temperature is ranged between 40 °F and 70 °F if salinity is kept in the range of 0.5–0.65 meq/ml. Moreover, for a pH value in the range of 6.8–7 and when the temperatures are between 40 °F and 70 °F, a higher volume of H2S is generated. The findings of this research help to manage the microbial souring issue in oil fields through controlling influential parameters achievable via carbonated smart water injection.

The Impact of Ecological Restoration on Biogeochemical Cycling and Mercury Mobilization in Anoxic Conditions on Former Mining Sites in French Guiana.

Successive years of gold mining in French Guiana has resulted in soil degradation and deforestation leading to the pollution and erosion of mining plots. Due to erosion and topography, gold panning sites are submitted to hydromorphy during rainfall and groundwater increases. This original study focused on characterizing the impact of hydromorphic anaerobic periods on bio-geochemical cycles. We sampled soil from five rehabilitated sites in French Guiana, including sites with herbaceous vegetation and sites restored with fabaceous plants, Clitoria racemosa (Cli) mon-oculture, Acacia mangium (Aca) monoculture, Clitoria racemosa and Acacia mangium (Mix) bi-culture. We conducted mesocosm experiments where soil samples were incubated in anaerobic conditions for 35 days. To evaluate the effect of anaerobic conditions on biogeochemical cycles, we measured the following parameters related to iron-reducing bacteria and sulfate-reducing bacteria metabolism throughout the experiment: CO2 release, carbon dissolution, sulphide production and sulphate mobilization. We also monitored the solubilization of iron oxyhydroxides, manganese oxides, aluminum oxides and mercury in the culture medium. Iron-reducing bacteria (IRB) and sulfate-reducing bacteria (SRB) are described as the major players in the dynamics of iron, sulfur and metal elements including mercury in tropical environments. The results revealed two trends in these rehabilitated sites. In the Aca and Mix sites, bacterial iron-reducing activity coupled with manganese solubilization was detected with no mercury solubilization. In herbaceous sites, a low anaerobic activity coupled with sulphide production and mercury solubilization were detected. These results are the first that report the presence and activity of iron- and sulfate-reductive communities at rehabilitated mining sites and their interactions with the dynamics of metallic elements and mercury. These results report, however, the positive impact of ecological restoration of mining sites in French Guiana by reducing IRB and SRB activities, the potential mobility of mercury and its risk of transfer and methylation.

Effect of crevice morphology on SRB activity and steel corrosion under marine foulers

Localized corrosion of submerged steel H-piles was detected in a Florida bridge spanning over a brackish river. Analysis of the water showed proliferation of sulfate reducing bacteria (SRB). The steel piles had coincident heavy marine growth that may support biofilms and biocorrosion. The objective of the research described here was to identify the role of the physical morphologies of macrofouling on SRB activity and the aggravation of microbiologically influences corrosion (MIC) of submerged steel bridge. Laboratory experiments were carried out in nutrient-rich environments inoculated with SRB, with both porous and laminate crevice conditions characteristic of soft and hard marine fouling. It was confirmed that SRB proliferation can occur within the crevice environments, but aeration levels under crevices with interaction with the bulk solution can affect SRB activity. Electrochemical impedance spectroscopy provided separation of environmental parameters and surface reaction parameters for the complicated systems relating to corrosion under the porous and laminate crevice geometries.

Effects of metals on activity and community of sulfate-reducing bacterial enrichments and the discovery of a new heavy metal-resistant SRB from Santos Port sediment (São Paulo, Brazil).

Sulfate-reducing bacteria (SRB) can be used to remove metals from wastewater, sewage, and contaminated areas. However, metals can be toxic to this group of bacteria. Sediments from port areas present abundance of SRB and also metal contamination. Their microbial community has been exposed to metals and can be a good inoculum for isolation of metal-resistant SRB. The objective of the study was to analyze how metals influence activity and composition of sulfate-reducing bacteria. Enrichment cultures were prepared with a different metal (Zn, Cr, Cu, and Cd) range concentration tracking activity of SRB and 16S rRNA sequencing in order to access the community. The SRB activity decreased when there was an increase in the concentration of the metals tested. The highest concentration of metals precipitated were 0.2 mM of Cd, 5.4 mM of Zn, 4.5 mM of Cu, and 9.6 mM of Cr. The more toxic metals were Cd and Cu and had a greater community similarity with less SRB and more fermenters (e.g., Citrobacter and Clostridium). Meanwhile, the enrichments with less toxic metals (Cr and Zn) had more sequences affiliated to SRB genera (mainly Desulfovibrio). A new Desulfovibrio species was isolated. This type of study can be useful to understand the effects of metals in SRB communities and help to optimize wastewater treatment processes contaminated by metals. The new Desulfovibrio species may be important in future studies on bioremediation of neutral pH effluents contaminated by metals.

Composition and Activity of N2-Fixing Microorganisms in Mangrove Forest Soils

Mangrove forests are considered to be a highly productive ecosystem, but they are also generally nitrogen (N)-limited. Thus, soil N2 fixation can be important for the stability of both mangrove ecosystem functions and upland N supply. This study evaluates the N2 fixation activity and composition of relevant microorganisms in two coastal mangrove forests—the Guandu mangrove in an upstream estuary and the Bali mangrove in a downstream estuary—using the acetylene reduction method, real-time polymerase chain reaction, and next-generation sequencing. The results demonstrated that ambient nitrogenase activity was higher in downstream mangrove forests (13.2–15.6 nmol h−1 g−1 soil) than in upstream mangrove forests (0.2–1.4 nmol h−1 g−1 soil). However, both the maximum potential nitrogenase activity and nitrogenase gene (nifH gene) copy number were found to be higher in the upstream than in the downstream mangrove forests, implying that the nitrogenase activity and diazotrophic abundance may not necessarily be positively correlated. In addition, amended MoO4 (which inhibits the activity of sulfate-reducing bacteria in N2-fixation) yielded low nitrogenase activity, and sulfate-reducing bacteria made up 20–50% of the relative diazotrophic abundance in the mangrove forests, indicating that these bacteria might be the major active diazotrophs in this environment.

A novel granular sludge-based and highly corrosion-resistant bio-concrete in sewers

Bio-concrete is known for its self-healing capacity although the corrosion resistance was not investigated previously. This study presents an innovative bio-concrete by mixing anaerobic granular sludge into concrete to mitigate sewer corrosion. The control concrete and bio-concrete (with granular sludge at 1% and 2% of the cement weight) were partially submerged in a corrosion chamber for 6 months, simulating the tidal-region corrosion in sewers. The corrosion rates of 1% and 2% bio-concrete were about 17.2% and 42.8% less than that of the control concrete, together with 14.6% and 35.0% less sulfide uptake rates, 15.3% and 55.6% less sulfate concentrations, and higher surface pH (up to 1.8 units). Gypsum and ettringite were major corrosion products but in smaller sizes on bio-concrete than that of control concrete. The total relative abundance of corrosion-causing microorganisms, i.e. sulfide-oxidizing bacteria, was significantly reduced on bio-concrete, while more sulfate-reducing bacteria (SRB) was detected. The corrosion-resistance of bio-concrete was mainly attributed to activities of SRB derived from the granular sludge, which supported the sulfur cycle between the aerobic and anaerobic corrosion sub-layers. This significantly reduced the net production of biogenic sulfuric acid and thus corrosion. The results suggested that the novel granular sludge-based bio-concrete provides a highly potential solution to reduce sewer corrosion.

Biostimulation of sulfate-reducing bacteria used for treatment of hydrometallurgical waste by secondary metabolites of urea decomposition by Ochrobactrum sp. POC9: From genome to microbiome analysis

Sulfate-reducing bacteria (SRB) are key players in many passive and active systems dedicated to the treatment of hydrometallurgical leachates. One of the main factors reducing the efficiency and activity of SRB is the low pH and poor nutrients in leachates. We propose an innovative solution utilizing biogenic ammonia (B–NH3), produced by urea degrading bacteria, as a pretreatment agent for increasing the pH of the leachate and spontaneously stimulating SRB activity via bacterial secondary metabolites. The selected strain, Ochrobactrum sp. POC9, generated 984.7 mg/L of ammonia in 24 h and promotes an effective neutralization of B–NH3. The inferred metabolic traits indicated that the Ochrobactrum sp. POC9 can synthesize a group of vitamins B, and the production of various organic metabolites was confirmed by GC-MS analysis. These metabolites comprise alcohols, organic acids, and unsaturated hydrocarbons that may stimulate biological sulfate reduction. With the pretreatment of B–NH3, sulfate removal efficiency reached ~92.3% after 14 days of incubation, whereas SRB cell count and abundance were boosted (~107 cell counts and 88 OTUs of SRB) compared to synthetic ammonia (S–NH3) (~103 cell counts and 40 OTUs of SRB). The dominant SRB is Desulfovibrio in both S–NH3 and B–NH3 pretreated leachate, however, it belonged to two different clades. By reconstructing the ecological network, we found that B–NH3 not only directly increases SRB performance but also promotes other strains with positive correlations with SRB.

Effects of silver nanoparticles added into polyurea coating on sulfate-reducing bacteria activity and electrochemical properties; an environmental nano-biotechnology investigation

In the present work, Ag nanoparticles were added to polyurea coating in order to improve its antibacterial and electrochemical properties in sulfide-reducing bacteria-containing media. To this end, Ag nano-powder was mixed with two component polyuria, and then the antibacterial behavior of the nanocomposite coating was studied in sulfate-reducing bacteria (SRB)-containing medium. The results revealed the inhibitory effects of nanocomposite coating on the formation of SRB biofilms on the samples. Moreover, the SRB population decreased in contact with the Ag nanoparticles-mixed coating over 7 days. Investigation of the growth and activity of the bacteria represented the effective antibacterial properties of Ag nanoparticles in the polyurea matrix. Furthermore, EIS (electrochemical impedance spectroscopy) measurements indicated that the corrosion properties of the nanocomposite coating improved considerably over 7 days. The coating resistance increased 2 times by adding Ag nanoparticles after 1 day and 3.3 times after 7 days. In accordance with the same results, the charge transfer resistance increased 1.5 times and 1.1 times by adding Ag nanoparticles after 1 day and 7 days, respectively. The improvement in the protective properties of the nanocomposite coating are reflected in the increase in both film and charge transfer resistance.

Ability of Sulfate Reducing Bacteria to Utilize Polymer and Rubber Materials

Polymer materials are an integral part of our lives, but their use is a global environmental problem. Despite this, the development of modern approaches to the utilization of used polymer and rubber materials is currently relevant, including the using of anaerobic microbial destruction of polymers by sulfatereducing bacteria. The aim of the work. To study the ability of sulfate-reducing bacteria to utilize rubber and polymer materials such as solid rubber, ethylene vinyl acetate and foamed polyethylene. Methods. Microbiological (cultivation of sulfate-reducing bacteria, method of serial dilutions), biochemical (Lowry method, measurement of enzymatic activity), physical and chemical (gravimetry, iodometry, potentiometry, gas chromatography-mass spectrometry). Results. It was shown that in the presence of the studied materials as the sole sources of carbon, the amount of sulfate-reducing bacteria increased by 2–3 orders compared to the control without adding the materials. On the 90th day of the experiment the destruction coefficients of the studied materials were low and reached KD=0.21–2.88%. In the cultivation medium with the introduced studied materials, the metabolic and enzymatic activity of sulfate-reducing bacteria are changed, in particular, the production of hydrogen sulfide in the presence of ethylene vinyl acetate and foamed polyethylene increased by 0.8–3 times, and rubber – decreased by 1.2–3.5 times. The catalase activity of the studied bacterial cultures was decreased by 1.4–3.4 times compared to the control without adding of materials. During the exposure period with adding the materials, the lipase activity of bacterial cultures decreased and in some cases almost disappeared. The introduction of materials led to increasing of the short-chain fatty acids synthesis by Desulfovibrio desulfuricans DSM642 and D. vulgaris DSM644 strains, while, on the contrary, Desulfovibrio sp. 10 strain showed the decreasing in acid production. The introduction of rubber only in D. vulgaris DSM644 culture leads to the increasing of acetic and propanoic acids synthesis by 59% and 49.5%, respectively, compared to the control without the introduction of the studied materials. The synthesis of acetic acid in the presence of foamed polyethylene and ethylene vinyl acetate in the cultural liquid of sulfate-reducing bacteria increased by 46.2–419.5% and 69.8–92.6%, and propane – by 23.1–46.2% and 71.9–159.0%, respectively. Conclusions. The presence in cultivation media of rubber, foamed polyethylene and ethylene vinyl acetate as a sole carbon sources led to the changes in enzymatic activity (catalase and lipase), the intensification of hydrogen sulfide synthesis by bacteria was observed as well as acetic, propanoic and butanoic acids synthesis increased. This indicates the potential of sulfate-reducing bacteria to utilize the studied materials via acid formation.

Influencing mechanism of Fe2+ on biomethane production from coal

The conversion of coal to biomethane is gaining considerable attention and can play a significant role in the field of energy research. To study the underlying influencing mechanism of adding exogenous Fe2+ on the process of the conversion of coal to biomethane, the biomethane production experiments were conducted using lignite and bituminous coal A as the substrate, and supplemented by different concentrations of ferrous ions. It is found that the optimum concentration of Fe2+ in the process of producing biomethane from coal is 10 mg/L. At this time, the cumulative methane production of lignite increased from 192 mL to 246 mL, and that of bituminous coal A increased from 165 mL to 197 mL, which increased by 13.5% and 10.8%. The added Fe2+ increased the content of iron in the humic acid state, which was easily absorbed and effectively utilized by microorganisms. This increase promoted the synthesis of hydrogenase and advanced the activity. Iron in the humic acid state also participated in the enzymatic reaction and promoted the activity of sulfate reducing bacteria and methanogens. Fe2+ in the free state formed FeS precipitates with the sulfur ion, which reduced the toxicity of soluble sulfides to bacteria. In both treated and untreated samples, the dominant methanogenic archaea changed from Methanobacterium before anaerobic fermentation to Methanosarcina after the reaction, indicating that Methanosarcina was favored under iron-abundant conditions. The experimental results improve understanding of the mechanism through which the addition of Fe2+ promotes the conversion of coal to biomethane.

The acid test: An experimental microarchaeological study of guano-driven diagenesis in tropical cave sediments

Caves in tropical regions form a key resource for those reconstructing human evolution and dispersals. However, the complex sedimentary records they contain remain under-interpreted because of the poorly constrained effects of humid tropical climates upon archaeological site formation processes. Guano-driven phosphatic diagenesis impacts archaeological preservation in caves, but atypical features observed in guano layers in prominent Southeast Asian archaeological sites suggested that hot and humid conditions had promoted the formation of distinctive sedimentary environments with unknown effects on assemblage taphonomy. Few reference data exist that are relevant to geomorphic processes in tropical caves and this laboratory-based modern analogue study was designed to conclusively relate analytical observations to sedimentary palaeoenvironments and explore their effects on assemblage taphonomy. Stratigraphic models were kept under simulated tropical conditions, each containing an identical range of faunal remains, organic materials and minerals, which was buried in wet bat guano. These were excavated, one per month over 24 months, while nine further stratigraphic models were used to control for environmental variables. Sedimentary environments were investigated using sedimentological characterisations of excavated sediments, while post-depositional alterations to buried materials were investigated through optical and scanning electron microscopic analysis of thin-section samples combined with chemical characterisations of excavated samples through Fourier-transform infrared spectroscopy (FTIR). Experimental conditions prevented the sediment acidification that is typically associated with guano-driven diagenesis, but buried materials were severely, and distinctively, diagenetically altered. Organic decomposition in guano, bamboo and charcoal was associated with the activities of sulphate-reducing bacteria, but diagenetic alterations affecting charcoal remain poorly resolved due to variation in the experimental assemblage. Bone was discoloured and affected by dissolution, recrystallisation and alteration to secondary minerals, including gypsum, while carbonates reprecipitated as calcium phosphates and non-stochiometric mineral species. Diagenesis of clay minerals was observed, but related diagenetic trajectories remain poorly resolved. These alterations provide micromorphological and mineralogical indicators of sedimentary palaeoenvironments in the earliest stages of burial and this experiment provides a framework within which to understand the taphonomy of archaeological materials in tropical caves.

Structure, diversity and potential metabolic activity of prokaryotic communities of Ebro Delta wetlands (Spain) as revealed by 16S rRNA gene amplicon sequencing

The monitoring of the structure and potential function of the prokaryotic assemblages of aquatic ecosystems can be used for the assessment of ecosystem health. In this work, we analysed by 16S rRNA gene amplicon massive sequencing the aquatic and sediment prokaryotic communities inhabiting three wetlands located in Ebro river Delta (Spain), which differ in their salinity and trophic status. We extracted the DNA from both matrices and sequenced the V4 region of the prokaryotic 16S rRNA gene by Illumina sequencing. The raw sequences obtained were processed and clustered in ZOTUs, which are sequences at 100% identity that were the basis for the structural and statistical analyses. Our results showed that water communities have less diversity and evenness than sediment communities. Moreover, statistical analyses showed that salinity is the main environmental factor that affects the structuration of sediment prokaryotic communities, while seasonality is also a very additional important environmental driver for aquatic communities. We also studied the relationship between the environmental factors and the potential metabolism of the aquatic and sediment prokaryotic communities, specifically for the main metabolic processes of the C-cycle. Focusing on sediment, we observed that methanogenic archaea are present not only in freshwater environments but also in the saline wetlands, though the observed methane emissions decreased with salinity. To explain this, we studied the potential activity of sulfate-reducing bacteria (SRB) and methanogenic archaea inferring the expression of genes dsrB and mcrA, which are gene markers for dissimilatory sulfate reduction and methanogenesis, respectively. We observed that, in saline wetlands, the potential activity of methanogens decreases because SRB bacteria outcompete them due to the higher sulfate availability enhancing sulfate-reduction. In the sediment communities of low salinity wetlands the relevance of methanogens is lower in terms of relative abundance, but the methane emissions are higher due to the lower sulfate availability. On the other hand, aquatic methanotrophic bacteria are very important in the net balance of methane emissions in Ebro Delta wetlands, as their relative abundance in the water column influences the amount of methane that is finally released to the atmosphere. In conclusion, our study deepens in the relationship between prokaryotic community structure and function in deltaic wetlands, giving a comprehensive overview of factors influencing the ecological health and certain processes, such as methane emissions, in deltaic systems.

Sulfur Metabolites Play Key System-Level Roles in Modulating Denitrification.

Competition between nitrate-reducing bacteria (NRB) and sulfate-reducing bacteria (SRB) for resources in anoxic environments is generally thought to be governed largely by thermodynamics. It is now recognized that intermediates of nitrogen and sulfur cycling (e.g., hydrogen sulfide, nitrite, etc.) can also directly impact NRB and SRB activities in freshwater, wastewater, and sediment and therefore may play important roles in competitive interactions. Here, through comparative transcriptomic and metabolomic analyses, we have uncovered mechanisms of hydrogen sulfide- and cysteine-mediated inhibition of nitrate respiratory growth for the NRB Intrasporangium calvum C5. Specifically, the systems analysis predicted that cysteine and hydrogen sulfide inhibit growth of I. calvum C5 by disrupting distinct steps across multiple pathways, including branched-chain amino acid (BCAA) biosynthesis, utilization of specific carbon sources, and cofactor metabolism. We have validated these predictions by demonstrating that complementation with BCAAs and specific carbon sources relieves the growth inhibitory effects of cysteine and hydrogen sulfide. We discuss how these mechanistic insights give new context to the interplay and stratification of NRB and SRB in diverse environments.IMPORTANCE Nitrate-reducing bacteria (NRB) and sulfate-reducing bacteria (SRB) colonize diverse anoxic environments, including soil subsurface, groundwater, and wastewater. NRB and SRB compete for resources, and their interplay has major implications on the global cycling of nitrogen and sulfur species, with undesirable outcomes in some contexts. For instance, the removal of reactive nitrogen species by NRB is desirable for wastewater treatment, but in agricultural soils, NRB can drive the conversion of nitrates from fertilizers into nitrous oxide, a potent greenhouse gas. Similarly, the hydrogen sulfide produced by SRB can help sequester and immobilize toxic heavy metals but is undesirable in oil wells where competition between SRB and NRB has been exploited to suppress hydrogen sulfide production. By characterizing how reduced sulfur compounds inhibit growth and activity of NRB, we have gained systems-level and mechanistic insight into the interplay of these two important groups of organisms and drivers of their stratification in diverse environments.

Stenopterygiids from the lower Toarcian of Beaujolais and a chemostratigraphic context for ichthyosaur preservation during the Toarcian Oceanic Anoxic Event

Abstract We report new ichthyosaur material excavated in lower Toarcian levels of the LafargeHolcim Val d'Azergues quarry in Beaujolais, SE France. A partially articulated skull and a smaller, unprepared but likely subcomplete skeleton preserved in a carbonate concretion are identified as stenopterygiids, a family of wide European distribution during the Early Jurassic. These specimens are among the finest preserved Toarcian exemplars known from Europe and, in one of them, soft tissue preservation is suspected. Their state of preservation is attributed to the combination of prolonged anoxic conditions near the water–sediment interface and early carbonate cementation resulting from the activity of sulfate-reducing bacteria. We also present carbon and strontium isotope values obtained from the study site that allow detailed temporal comparisons with other Toarcian vertebrate-yielding sites and environmental perturbations associated with the Toarcian Oceanic Anoxic Event (T-OAE). These comparisons suggest that the relatively high abundance and good preservation state of Toarcian vertebrates was favoured by a prolonged period of low bottom water oxygenation and accumulation rates. The environmental conditions that prevailed during the T-OAE were probably responsible for the extensive nature of Lagerstätte-type deposits with exceptional preservation of marine organisms. Testing whether the T-OAE had a biological impact on marine vertebrates requires a precise chemostratigraphic context of the fossil record spanning the Pliensbachian–Toarcian interval.

Effect of Cu2+ and Cd2+ on the growth and sulfidogenic activity of sulfate-reducing bacteria under using aromatic hydrocarbons

Purification of the aquatic environment from substances of organic and inorganic matter is an urgent problem nowadays. Falling into the water of insufficiently treated effluents significantly impairs water quality and the condition of water bodies in general. Aromatic compounds, in particular toluene and xylene, are quite common pollutants in the aquatic environment. In addition to compounds of organic nature, wastewater contains many inorganic substances and heavy metal ions. Among the common methods of detoxification of the environment, biological ones play a leading role, as they are cost-effective and environmentally safe. One of the promising methods of purification is the usage of microorganisms, in particular sulfate-reducing bacteria. The influence of heavy metal ions on the accumulation of biomass and hydrogen sulfide by Desulfotomaculum sp. AR1 and D. desulfuricans Ya-11 bacteria during the growth in a medium with toluene and xylene is studied. The ability of sulfate-reducing bacteria Desulfotomaculum sp. AR1 and D. desulfuricans Ya-11 to grow with the simultaneous presence of aromatic compounds and heavy metal ions into the environment indicates their high potential in the usage to purify the aquatic environment from these contaminants. The inhibitory effect of metal ions on the process of reduction of sulfate ions by the studied bacteria, and, as a consequence, the accumulation of less toxic hydrogen sulfide, is shown. The influence of the source of carbon (sodium lactate/xylene/toluene) and heavy metal ions on the growth of bacteria Desulfotomaculum sp. AR1 and D. desulfuricans Ya-11 is analysed. It is shown that the accumulation of biomass by bacteria Desulfotomaculum sp. AR1 and D. desulfuricans Ya-11 are affected by both the nature of the electron donor and the presence of Cu2+ and/or Cd2+ ions in the medium. Penetrating into living cells, heavy metal ions disrupt their vital functions, but heavy metals are toxic only in the form of ions, but if they are translated into a bound form, they lose their toxic properties. The ability of the studied bacteria to precipitate Cu2+ and Cd2+ ions in the form of insoluble metal sulfides was revealed. Thus, the content of hydrogen sulfide in the aqueous medium can be adjusted, and in turn, it can be purified from heavy metal ions. According to the obtained results, sulfate-reducing bacteria Desulfotomaculum sp. AR1 and D. desulfuricans Ya-11 can be considered as promising in the development of methods for purification of the aquatic environment from heavy metal ions, in particular Cu2+ and Cd2+

Long-term souring treatment using nitrate and biocides in high-temperature oil reservoirs

The biogenic production of hydrogen sulfide (H2S) by sulfate-reducing bacteria (SRB) and consequently the souring of reservoirs are still major problems in oil industry. Biocides and/or nitrate are used to control SRB activity in oil reservoirs, but long-term studies are still needed to prove their efficacy. In this study, two high-temperature (80–84 °C) oil reservoirs were analyzed over three years. Nitrate and tetrakishydroxymethyl phosphonium sulfate (THPS) were added to the water injection system (WI) at the beginning of secondary oil recovery in oil reservoir 1, while nitrate was only added 19 months after the beginning of secondary oil recovery in oil reservoir 2. The H2S concentration was quantified monthly in production wells, and the total bacterial community (based on the gene coding for 16S rRNA) and SRB (based on dsrA and apsAB genes) were determined using fluorescence in situ hybridization (FISH) and PCR-DGGE analyses. Nitrate plus THPS controlled H2S production for 34 months in oil reservoir 1. THPS injection in oil reservoir 2 controlled H2S levels for 17 months, and the further addition of nitrate in water injection did not control H2S production. PCR-DGGE analyses and the molecular identification of the dominant groups showed a predominance of thermophilic bacteria, including different SRB (such as Desulfocaldus and Desulfonauticus) and nitrate-reducing bacteria (NRB – Marinobacter) in oil reservoir 1 and mesophilic SRB (Desulfovibrio) and NRB (Halomonas and Acinetobacter) in oil reservoir 2. The strategy chosen during secondary oil recovery modulated the microbial community and, consequently, changed the dynamics of H2S production.

Influence of oligomethylenaryl sulphonates based on the light gas oil of catalytic cracking on the process of biocorrosion

This article presents the results of studies in the field of synthesis of water-soluble salts of oligomethylene aryl sulfonates synthesized using aromatic hydrocarbons contained in the gas oil fraction of the catalytic cracking process of oil as raw materials. Based on the synthesized various salts of oligoaromatic sulfonic acids (sodium, potassium, ammonium salts), solutions of various concentrations (35; 75; 150; 200 mg/l) were prepared and their effect on the vital activity of sulfate-reducing bacteria at a temperature of 30…32 °С for 7…14 days was studied. It was found that complex salts synthesized on the basis of oligomeric sulfonic acids of aromatic hydrocarbons of the gas oil fraction (N-1, N-2, N-3) at a concentration of 150 mg/l exhibit more than 90%, and at a concentration of 200 mg/l, 100% bactericidal effect and completely inhibits the growth of bacteria. It was revealed that the synthesized salts of sulfonic acids exhibit a relatively higher antimicrobial activity against SRB than the industrial bactericidal inhibitors AMDOR-IK-7 and AMDOR-IK-10 taken as a reference. Based on the studies, it was found that the synthesized salts of oligosulfonic acids completely inhibit the growth of sulfate-reducing bacteria at much lower concentrations compared to the industrially used bactericidal inhibitors taken as a reference. In particular, at a concentration of 150 mg/l, the bactericidal effect is more than 90% against 75…80% for the standard.

Application of EIS to Assess Microbiologically Influenced Steel Corrosion in Marine Fouling Crevice Conditions

Microbiologically influenced corrosion (MIC) can cause severe degradation of civil infrastructure. Recently, severe localized corrosion of steel H-piles submerged in a brackish natural water in a Florida bridge was associated with MIC and fouling (Permeh et al., 2017). The localized corrosion cells/pits were of up to 3" in diameter and penetrated through the steel thickness. Microbiological and chemical analysis of the water samples showed a high population of sulfate reducing bacteria (SRB) and a high concentration of sulfate ions amongst other nutrients. The steel piles had noticeable heavy marine growth which were thought to have an effect on the corrosion process by supporting biofilm development, creating localized corrosion and differential aeration cells (Little et al, 2007). In the work described here electrochemical impedance spectroscopy (EIS) was conducted to characterize the development of biofilm in association with fouling crevice environments.Electrochemical impedance spectroscopy (EIS) has been widely used to assess the electrochemical properties of corrosion systems and has been applied to assess physical biofilm conditions for microbiologically influenced corrosion (MIC) (Mansfeld , 2005). EIS measurements over a wide range of frequencies can be used to identify the electrical characteristics associated with the biofilm and the steel substrate. Both laboratory and field exposure tests were conducted. Field exposure tests included long term exposure (~300 days) of steel coupons at a Florida bridge site that sustained macro- and microfouling organisms. Laboratory tests were conducted in nutrient-rich test solutions inoculated with sulfate reducing bacteria (SRB) in either de-aerated or naturally aerated conditions as well as with idealized crevice geometries. EIS testing was made at the OCP condition with 10 mV AC perturbation voltage from frequencies 100 kHz > f >100 mHz.EIS of the specimens inoculated with SRB and with crevices resulted in impedance responses with multiple loops in the Nyquist diagram. Fitting of the impedance response to equivalent circuit analogs were made to identify biofilm, surface layers, and the steel interfacial characteristics during the experimental exposure (Permeh et al.,2019). For non-crevice specimens without SRB inoculations, the impedance response related to the solution resistance, steel interfacial capacitance and charge transfer resistance, characterized by the Randles circuit. However, for the inoculated specimens, impedance dispersion at high frequencies (sometimes showing a loop in the Nyquist diagram) on first approximation was related to the capacitive and resistive characteristics of the biofilm. In crevice environments, a more complicated behavior arose due to uneven current distribution and heterogeneous impedance within the crevice. The impedance behavior for the porous and laminate crevices can be characterized by multiple time constants associated with the crevice outer material, steel interface, and the current distribution effects in the crevice that can be considered by treatments such as a transmission line. In the inoculated non-crevice specimens, the high frequency impedance dispersion was more readily apparent in the Bode phase angle plot. In that representation, the impedance initially showed a uniform valley with a distinct trough between 10 and 100 mHz. With time, two unique troughs developed at frequencies below 1 Hz (Figure 1) for the inoculated specimens. An increase in capacitance was attributed to biofilm growth.In part to provide a quantitative comparison of the overall impedance of the systems (despite the complicating factors for the crevice specimens), on first approach, the total impedance at 100 mHz (|Z100mHz¬|) was compared. The differences in the total impedance for the various test conditions would reflect the resistive and capacitive electrical behavior of the electrolyte, biofilm, and the steel interface that in turn are directly or indirectly related to SRB activity. EIS identified the development of surface films including by an increase in its capacitive behavior that resulted in lower relative total impedance at a given low frequency (i.e. 100 mHz). Test results confirmed that SRB proliferation and corrosion can occur as the fouling macroorganism can accommodate different environmental condition.

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.

Trace element fixation in sediments rich in organic matter from a saline lake in tropical latitude with hydrothermal inputs (Sochagota Lake, Colombia): The role of bacterial communities

We studied the relationships between the trace element concentration in sediments from a saline lake at a tropical latitude (Sochagota Lake, Colombia) containing hydrothermal and anthropic inputs with the organic matter content, the mineral assemblage composition and the activity of the bacterial communities of the sediments. Organic matter-poor sediments (TOC < 0.7%) with quartz and kaolinite near the southern entrance of the lake were enriched in Zr (up to 603 mg/kg) and some major detrital elements (Na, Ti, Al and Si). Fine-sized clay-rich sediments deposited in the deep zones of the lake (central and northern segments) were characterized by substantial organic matter (up to 11.10%) and the crystallization of S-bearing minerals, clay mineral mixed layers and illite. These sediments were enriched in S, Fe, Zn, Mo, Rb, Co, K, Cr, Sb, Ni, As, Ba, Cu, Mn, Pb, P, Mg, and Sr. The presence of Fe sulfide nanoparticles enriched in heavy metals encrusting microbial cells and a dominant sulfate-reducing bacteria (SRB) community (Desulfatiglans, Desulfobacterales and Sva0485) suggested that the precipitation of the hydrothermal S and the accumulation of trace elements in the sediments was regulated by SRB activity. The crystallization of S°, barite and calcite and the good correlations between Ba, Sr and Ca indicated that previously precipitated sulfide can be oxidized by the activity of a relevant sulfur-oxidizing bacterial community (Thioalkalimicrobium, Sulfurovum, Arcobacter and Sulfurimonas), possibly facilitating the release of the metals.