Inhibition Of Sulfate-reducing Bacteria Research Articles

Nitrate and oxygen significantly changed the abundance rather than structure of sulphate-reducing and sulphur-oxidising bacteria in water retrieved from petroleum reservoirs.

Sulphate-reducing bacteria (SRB) are the main culprits of microbiologically influenced corrosion in water-flooding petroleum reservoirs, but some sulphur-oxidising bacteria (SOB) are stimulated when nitrate and oxygen are injected, which control the growth of SRB. This study aimed to determine the distributions of SRB and SOB communities in injection-production systems and to analyse the responses of these bacteria to different treatments involving nitrate and oxygen. Desulfovibrio, Desulfobacca, Desulfobulbus, Sulfuricurvum and Dechloromonas were commonly detected via 16S rRNA gene sequencing. Still, no significant differences were observed for either the SRB or SOB communities between injection and production wells. Three groups of water samples collected from different sampling sites were incubated. Statistical analysis of functional gene (dsrB and soxB) clone libraries and quantitative polymerase chain reaction showed that the SOB community structures were more strongly affected by the nitrate and oxygen levels than SRB clustered according to the sampling site; moreover, both the SRB and SOB community abundances significantly changed. Additionally, the highest SRB inhibitory effect and the lowest dsrB/soxB ratio were obtained under high concentrations of nitrate and oxygen in the three groups, suggesting that the synergistic effect of nitrate and oxygen level was strong on the inhibition of SRB by potential SOB.

Niche Modification by Sulfate-Reducing Bacteria Drives Microbial Community Assembly in Anoxic Marine Sediments.

Sulfate-reducing bacteria (SRB) are essential functional microbial taxa for degrading organic matter (OM) in anoxic marine environments. However, there are little experimental data regarding how SRB regulates microbial communities. Here, we applied a top-down microbial community management approach by inhibiting SRB to elucidate their contributions to the microbial community during OM degradation. Based on the highly replicated microcosms (n = 20) of five different incubation stages, we found that many microbial community properties were influenced after inhibiting SRB, including the composition, structure, network, and community assembly processes. We also found a strong coexistence pattern between SRB and other abundant phylogenetic lineages via positive frequency-dependent selection. The relative abundances of the families Synergistaceae, Peptostreptococcaceae, Dethiosulfatibacteraceae, Prolixibacteraceae, Marinilabiliaceae, and Marinifilaceae were simultaneously suppressed after inhibiting SRB during OM degradation. A close association between SRB and the order Marinilabiliales among coexisting taxa was most prominent. They contributed to preserved modules during network successions, were keystone nodes mediating the networked community, and contributed to homogeneous ecological selection. The molybdate tolerance test of the isolated strains of Marinilabiliales showed that inhibited SRB (not the inhibitor of SRB itself) triggered a decrease in the relative abundance of Marinilabiliales. We also found that inhibiting SRB resulted in reduced pH, which is unsuitable for the growth of most Marinilabiliales strains, while the addition of pH buffer (HEPES) in SRB-inhibited treatment microcosms restored the pH and the relative abundances of these bacteria. These data supported that SRB could modify niches to affect species coexistence. IMPORTANCE Our model offers insight into the ecological properties of SRB and identifies a previously undocumented dimension of OM degradation. This targeted inhibition approach could provide a novel framework for illustrating how functional microbial taxa associate the composition and structure of the microbial community, molecular ecological network, and community assembly processes. These findings emphasize the importance of SRB during OM degradation. Our results proved the feasibility of the proposed study framework, inhibiting functional taxa at the community level, for illustrating when and to what extent functional taxa can contribute to ecosystem services.

The potent effects of polyoxometalates (POMs) on controlling sulfide and methane production from sewers

Although the dose of biocides to sewers could control sulfide and methane production, the high resistance of sulfate-reducing bacteria (SRB) to biocides would increase dosing frequency and thereby enlarge chemical costs. Polyoxometalates (POMs, Group VI oxyanion), as a specific inhibitor of SRB, has been applied for sulfide control in oil fields and anaerobic digesters, but not demonstrated in sewers. This study filled such knowledge gap and investigated its feasibility for methane alleviation. Long-term monitoring demonstrated that one-time dosing of 2 mM POMs into sewers immediately reduced sulfide production by >90 %. And the time for recovering 50 % sulfide production was beyond 20 days, which was much more outstanding than other chemicals. POMs combined with a low level of free nitrous acid (0.045 mg-N/L) could overcome the relatively low methane control of the single POMs dosing, with 80 % suppression of methanogenic activity for 30 days. Meanwhile, the POMs-based strategy reduced the average organic carbon loss by 18 %. Furthermore, the beneficial side-effect of in-sewer POMs-dosing on downstream nitrogen removal could be achieved with the confluence of sewage. Model-analysis indicated the recovery of sulfide and methane was a re-formation process of biofilms. Mechanistic study elucidated POMs broke the extracellular polymeric substances of biofilms and damaged the cell membranes due to accumulations of intracellular reactive oxygen species. This suppressed microbial metabolic activities including organics dehydrogenation, energy provision and electron transfer processes, and inhibited key enzymatic activities. Microbial community analysis suggested POMs shifted microbes towards against hydrolysis, acidogenesis, dissimilatory sulfate reduction and methanogenesis. Further, predicted functional genes revealed that metabolic pathways were mostly down-regulated by POMs. This study provided a better understanding for controlling sulfide and methane in sewers using biocides.

Unravelling biogeochemical drivers of methylmercury production in an Arctic fen soil and a bog soil

Arctic tundra soils store a globally significant amount of mercury (Hg), which could be transformed to the neurotoxic methylmercury (MeHg) upon warming and thus poses serious threats to the Arctic ecosystem. However, our knowledge of the biogeochemical drivers of MeHg production is limited in these soils. Using substrate addition (acetate and sulfate) and selective microbial inhibition approaches, we investigated the geochemical drivers and dominant microbial methylators in 60-day microcosm incubations with two tundra soils: a circumneutral fen soil and an acidic bog soil, collected near Nome, Alaska, United States. Results showed that increasing acetate concentration had negligible influences on MeHg production in both soils. However, inhibition of sulfate-reducing bacteria (SRB) completely stalled MeHg production in the fen soil in the first 15 days, whereas addition of sulfate in the low-sulfate bog soil increased MeHg production by 5-fold, suggesting prominent roles of SRB in Hg(II) methylation. Without the addition of sulfate in the bog soil or when sulfate was depleted in the fen soil (after 15 days), both SRB and methanogens contributed to MeHg production. Analysis of microbial community composition confirmed the presence of several phyla known to harbor microorganisms associated with Hg(II) methylation in the soils. The observations suggest that SRB and methanogens were mainly responsible for Hg(II) methylation in these tundra soils, although their relative contributions depended on the availability of sulfate and possibly syntrophic metabolisms between SRB and methanogens.

Inhibition of sulfate-reducing bacteria with formate.

Despite hostile environmental conditions, microbial communities have been found in µL-sized water droplets enclosed in heavy oil of the Pitch Lake, Trinidad. Some droplets showed high sulfate concentrations and surprisingly low relative abundances of sulfate-reducing bacteria in a previous study. Hence, we investigated here whether sulfate reduction might be inhibited naturally. Ion chromatography revealed very high formate concentrations around 2.37 mM in 21 out of 43 examined droplets. Since these concentrations were unexpectedly high, we performed growth experiments with the three sulfate-reducing type strains Desulfovibrio vulgaris, Desulfobacter curvatus, and Desulfococcus multivorans, and tested the effects of 2.5, 8, or 10 mM formate on sulfate reduction. Experiments demonstrated that 8 or 10 mM formate slowed down the growth rate of D. vulgaris and D. curvatus and the sulfate reduction rate of D. curvatus and D. multivorans. Increasing formate concentrations delayed the onsets of growth and sulfate reduction of D. multivorans, which were even inhibited completely while formate was added constantly. Contrary to previous studies, D. multivorans was the only organism capable of formate consumption. Our study suggests that formate accumulates in the natural environment of the water droplets dispersed in oil and that such levels are very likely inhibiting sulfate-reducing microorganisms.

Newly imine-azo dicationic amphiphilic for corrosion and sulfate-reducing bacteria inhibition in petroleum processes: Laboratory and theoretical studies

Oil and gas process faces a large dilemma during the acidizing job. So, dicationic surfactant namely; 1-dodecyl-3-((E)-(4-(((E)-(1-dodecylpyridin-1-ium-4-yl) methylene)amino)-2-hydroxyphenyl) diazenyl)pyridin-1-iumdibromide (SDCAC) was synthesized. Spectroscopic and CHN elemental analysis studies confirmed the SDCAC structure. SDCAC has Surface active properties. The anticorrosion performance of SDCAC for carbon steel (CS) in 1.0 M HCl has been validated gravimetrically and electrochemically accompanied with surface analysis studies. SDCAC enhances the resistance of CS corrosion by 98%. Tafel data classify SDCAC as a hybrid anticorrosive substance. Adsorption of SDCAC is more fitted to the Langmuir adsorption isotherm model. Theoretical indices of SDCAC affirm its tendency toward adsorption. The activity of SDCAC against sulfate reducing bacteria (SRB) has been examined and promising outcomes have been achieved. According to the findings of this investigation, the SDCAC can reduce SRB growth from 107 to102 cell/ml.

Sulfidogenic Microbial Communities of the Uzen High-Temperature Oil Field in Kazakhstan.

Application of seawater for secondary oil recovery stimulates the development of sulfidogenic bacteria in the oil field leading to microbially influenced corrosion of steel equipment, oil souring, and environmental issues. The aim of this work was to investigate potential sulfide producers in the high-temperature Uzen oil field (Republic of Kazakhstan) exploited with seawater flooding and the possibility of suppressing growth of sulfidogens in both planktonic and biofilm forms. Approaches used in the study included 16S rRNA and dsrAB gene sequencing, scanning electron microscopy, and culture-based techniques. Thermophilic hydrogenotrophic methanogens of the genus Methanothermococcus (phylum Euryarchaeota) predominated in water from the zone not affected by seawater flooding. Methanogens were accompanied by fermentative bacteria of the genera Thermovirga, Defliviitoga, Geotoga, and Thermosipho (phylum Thermotogae), which are potential thiosulfate- or/and sulfur-reducers. In the sulfate- and sulfide-rich formation water, the share of Desulfonauticus sulfate-reducing bacteria (SRB) increased. Thermodesulforhabdus, Thermodesulfobacterium, Desulfotomaculum, Desulfovibrio, and Desulfoglaeba were also detected. Mesophilic denitrifying bacteria of the genera Marinobacter, Halomonas, and Pelobacter inhabited the near-bottom zone of injection wells. Nitrate did not suppress sulfidogenesis in mesophilic enrichments because denitrifiers reduced nitrate to dinitrogen; however, thermophilic denitrifiers produced nitrite, an inhibitor of SRB. Enrichments and a pure culture Desulfovibrio alaskensis Kaz19 formed biofilms highly resistant to biocides. Our results suggest that seawater injection and temperature of the environment determine the composition and functional activity of prokaryotes in the Uzen oil field.

Environmental Impact of Sulfate-Reducing Bacteria, Their Role in Intestinal Bowel Diseases, and Possible Control by Bacteriophages

Sulfate-reducing bacteria (SRB) represent a group of prokaryotic microorganisms that are widely spread in the anoxic environment (seabed, riverbed and lakebed sediments, mud, intestinal tract of humans and animals, metal surfaces). SRB species also have an impact on processes occurring in the intestinal tract of humans and animals, including the connections between their presence and inflammatory bowel disease (IBD). Since these SRB can develop antimicrobial resistance toward the drugs, including antibiotics and antimicrobial agents, bacteriophages could represent an additional potential effective treatment. The main objectives of the review were as follows: (a) to review SRB (both from intestinal and environmental sources) regarding their role in intestinal diseases as well as their influence in environmental processes; and (b) to review, according to literature data, the influence of bacteriophages on SRB and their possible applications. Since SRB can have a significant adverse influence on industry as well as on humans and animals health, phage treatment of SRB can be seen as a possible effective method of SRB inhibition. However, there are relatively few studies concerning the influence of phages on SRB strains. Siphoviridae and Myoviridae families represent the main sulfide-producing bacteria phages. The most recent studies induced, by UV light, bacteriophages from Desulfovibrio vulgaris NCIMB 8303 and Desulfovibrio desulfuricans ATCC 13541. Notwithstanding costly and medically significant negative impacts of phages on SRB, they have been the subject of relatively few studies. The current search for alternatives to chemical biocides and antibiotics has led to the renewed interest in phages as antibacterial biocontrol and therapeutic agents, including their use against SRB. Hence, phages might represent a promising treatment against SRB in the future.

Acid mine drainage treatment using zero-valent iron nanoparticles in biochemical passive reactors

ABSTRACT Acid mine drainage (AMD) is the major effluent generated from metal and coal mines, causing serious ecological risks and degradation of aquatic habitats and surrounding soil quality. Biochemical passive reactors (BPRs) are an option for improving AMD affected water. This study investigates the effect of the size and concentration of zerovalent iron nanoparticles (nZVI) on the efficiency of batch BPRs during AMD remediation. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were also used as complementary techniques for the investigation of the changes in microbial cells and nZVI properties after the AMD remediation. The results from the batch experiment showed that the concentration of nZVI increases the pH and decreases ORP during AMD treatment, thus favouring the removal of metals. The results also suggest that metal sulfide precipitation occurred in all the batch with reactive mixture but was greater in reactors amended with nZVI of larger size. This study revealed that the presence of nZVI in the BPR leads to metal removal as well as the inhibition of sulfate-reducing bacteria (SRB) activity. Microscopy study indicated that the addition of nZVI creates a morphological change on certain microorganisms in which the cellular membrane was fully covered with nZVI, inducing cell lysis process. These results show that nZVI is a promising reactive material for the treatment of AMD in BPR systems.

Ferric iron stimulation in marine SMFCs: Impact on the microbial structure evolution in contaminated sediments with low and high molecular weight PAHs

The impact of ferric iron stimulation on the evolution of microbial structure in marine sediment microbial fuel cells (SMFCs), operated for the bioremediation of a complex mixture of low and high molecular weight PAHs (naphthalene, fluorene, pyrene and benzo(a)pyrene), was assessed. Microbial evolution profiles showed high relative abundances of exoelectrogenic iron-reducing bacteria throughout the biodegradation, namely Geoalkalibacter, under ferric iron stimulation and anode reducing conditions, irrespective of sulfate reducing bacteria (SRB) inhibition. Highest PAHs removal was measured in the absence of anode reduction, under Fe stimulation and SRB inhibition, reaching 40.85% for benzo(a)pyrene, the most persistent PAH used in this study. Results suggest that amendment of contaminated sediment with ferric iron could constitute a better bioremediation strategy than using SMFCs. This becomes significant when considering the well-established and dominant indigenous SRB population in marine sediments that usually limits the performance of the anode as a terminal electron acceptor in marine SMFCs.

Graphene oxide/silver nanostructure as a green anti-biofouling composite toward controlling the microbial corrosion

Microbiologically influenced corrosion is a serious problem in the oil and gas industry, which leads to both economical losses and environmental pollutions. To control biocorrosion and prevent the problems, using biocides is the main solution. Recently, nanomaterials have been introduced as a new generation of biocides to control the biocorrosion. In this study, graphene oxide/silver nanostructure was synthetized, and its biocidal effect was evaluated by a dose–response test. The response surface methodology in the Design-Expert software was used to analyze the result, and to determine the optimum concentration of nanostructure to inhibit sulfate reducing bacteria, which was 80 mg/L. The corrosion morphology and the composition of the formed corrosion products were studied using surface analysis methods. The result illustrated the uniform corrosion and significantly reduced amount of iron sulfide in the presence of nanostructure, due to the inhibition of sulfate reducing bacteria. In comparison, the pitting corrosion was observed on the surface of the exposed coupon to the bacteria, and the high presence of iron sulfide in the corrosion products. The corrosion behavior of steel in the presence of the bacteria and the nanostructure was investigated via electrochemical impedance spectroscopy and Tafel polarization techniques. Corrosion test result indicated that the addition of the nanostructure increased the charge transfer resistance, resulting in the reduction in corrosion rate. This is attributed to preventing the production of biofilm by the nanostructure and the formation of a protective film in the presence of graphene oxide nanosheets.

Charge-reversal surfactant antibiotic material for reducing microbial corrosion in petroleum exploitation and transportation.

The corrosions caused by sulfate-reducing bacteria (SRB) are serious problems in petroleum exploitation and transportation, which can lead to safety problems, environmental pollutions, and economic losses. Here, a charge-reversal surfactant antibiotic material N-dodecyl-1-carboxylic acid-1-cyclohexenyl-2-carboxamide (C12N-DCA) is designed and synthesized. C12N-DCA is a negatively charged surfactant, which cannot be adsorbed by soil and rock in a large amount. Therefore, it can reach the "lesion location", with enough concentration. After being hydrolyzed and charge reversed under the acceleration of H2S produced by SRB, C12N-DCA becomes a positively charged surfactant dodecane ammonium salt to kill SRB. Through a simulating experiment, it is found that C12N-DCA can reach the SRB inhibition ratio of almost 100%, and it can reduce iron corrosion by 88%. Such an antibiotic material or its homologs may be added to the chemical flooding fluids, killing SRB during petroleum exploitation and reducing the SRB-induced corrosion in the petroleum exploitation and transportation.

Bio-competitive exclusion of sulfate-reducing bacteria and its anticorrosion property

The bio-competitive exclusion (BCX) method is a practical, environment-friendly, and low-cost method of controlling sulfate-reducing bacteria (SRB) and focuses on research and preliminary applications. In this study, a nitrate-reducing bacteria (NRB) were screened and selected from oil-producing water and identified as heterotrophic Pseudomonas sp. through 16S rDNA. The NRB activation and the SRB inhibition systems were studied via the addition of the bio-activators NO3− and NO2−. In addition, the synergistic inhibitory effect of NRB and molybdate on SRB was studied. Results showed that the inhibitory effect of NO2− was better than that of NO3−. At NO3− to NO2− ratio of 1:4, the inhibitory effect was optimum. The addition of 5% activated NRB and a small amount of molybdic acid salt played a synergistic effect. The optimal inhibition system contained the following: 5% NRB, NO3−/NO2− of 1:4, and the amount of molybdate was 1/5 that of NO3−. In this inhibition system, S2− can maintain an extremely low content, and SRB activity was well inhibited. Static corrosion simulation experiments showed that SRB was the main cause of corrosion. The effects of biological inhibitors, fungicides, and corrosion inhibitors on the corrosion inhibition were investigated. Results showed that the corrosion rate of biological inhibitors was the lowest, and the best effect of corrosion inhibition was achieved. The surface morphology of the corroded steel sheet was analyzed via scanning electron microscope. In addition, the surface corrosion of the steel sheet was low, and no pitting was observed.

Growth inhibition of sulfate-reducing bacteria for trichloroethylene dechlorination enhancement

Trichloroethylene (TCE) is a frequently found organic contaminant in polluted-groundwater. In this microcosm study, effects of hydrogen-producing bacteria [Clostridium butyricum (Clostridium sp.)] and inhibitor of sulfate-reducing bacteria (SRB) addition on the enhancement of TCE dechlorination were evaluated. Results indicate that Clostridium sp. supplement could effectively enhance TCE reductive dechlorination (97.4% of TCE removal) due to increased hydrogen concentration and Dehalococcoides (DHC) populations (increased to 1 × 104 gene copies/L). However, addition of Clostridium sp. also caused the increase in dsrA (dissimilatory sulfide reductase subunit A) (increased to 2 × 108 gene copies/L), and thus, part of the hydrogen was consumed by SRB, which would limit the effective application of hydrogen by DHC. Control of Clostridium sp. addition is a necessity to minimize the adverse impact of Clostridium sp. on DHC growth. Ferric citrate caused the slight raise of the oxidation-reduction state, which resulted in growth inhibition of SRB. Molybdate addition inhibited the growth of SRB, and thus, the dsrA concentrations (dropped from 4 × 107 to 9 × 105 gene copies/L) and sulfate reduction efficiency were decreased. Increased DHC populations (increased from 8 × 103 to 1 × 105 gene copies/L) were due to increased available hydrogen (increased from 0 to 2 mg/L), which enhanced TCE dechlorination (99.3% TCE removal). Metagenomic analyses show that a significant microbial diversity was detected in microcosms with different treatments. Clostridium sp., ferric citrate, and molybdate addition caused a decreased SRB communities and increased fatty acid production microbial communities (increased from 4.9% to 20.2%), which would be beneficial to the hydrogen production and TCE dechlorination processes.

Towards sulfide removal and sulfate reducing bacteria inhibition: Function of biosurfactants produced by indigenous isolated nitrate reducing bacteria

The effectiveness of nitrate-mediated souring control highly depends on the interactions of sulfate reducing bacteria (SRB) and nitrate reducing bacteria (NRB). Biosurfactants produced by natural NRB are promising bio-agents for enhancing NRB competence towards SRB. However, the function of NRB-produced biosurfactants in NRB-SRB interactions remains unexplored due to the rarely successful isolation of natural biosurfactant-producing NRB. Hereby, biosurfactant-aided inhibitory control of SRB strain Desulfomicrobium escambiense ATCC 51164 by biosurfactant-producing NRB strain Pseudomonas stutzeri CX3, reported in our previous work, was investigated. Under non-sour conditions, insufficient nitrate injection resulted in limited SRB inhibition. Phospholipid fatty acid (PLFA) biomarkers traced the overall bacterial responses. Compositional PLFA patterns revealed biosurfactant addition benefitted both SRB and NRB towards stressful conditions. Under sour conditions, nitrite oxidation of sulfide proved to be the primary mechanism for sulfide removal. The subsequent elevation of redox potential and pH inhibited SRB activities. NRB-produced biosurfactants significantly enhanced SRB inhibition by NRB through more efficient sulfide removal and effective duration of nitrate in the microcosms. Biosurfactants specially produced by the NRB strain are for the first time reported to significantly strengthen SRB inhibition by NRB via reduced nitrate usage and prolonged effective duration of nitrate, which has encouraging potential in nitrate-dependent souring control.

Microbial sulfate reduction decreases arsenic mobilization in flooded paddy soils with high potential for microbial Fe reduction

Arsenic (As) tends to mobilize in flooded paddy soil due to the reductive dissolution of the iron (oxyhydr)oxides to which As sorbs, resulting in elevated As accumulation in rice that poses a potential risk to the food safety and human health. Microbial sulfate reduction is an important biogeochemical process in paddy soils, but its impact on As mobilization remains poorly understood. In this study, we incubated eight As-contaminated paddy soils under flooded conditions to investigate the effect of sulfate addition on As mobility. Porewater Fe and As concentrations and As species were determined. Among the eight soils, an addition of 50 mg S kg−1 as sodium sulfate decreased porewater arsenite only in two soils, which also showed a high mobilization of Fe2+. Further experiments showed that the addition of sulfate to these two soils stimulated microbial sulfate reduction but decreased porewater concentrations of both arsenite and Fe2+. Additionally, the supply of sulfate increased the fractions of As associated with acid volatile sulfides in the solid phase and decreased As uptake by rice in pot experiments under similar conditions. The effect of sulfate addition on porewater As was diminished by the addition of molybdate, an inhibitor of sulfate reducing bacteria. These results suggest the formation of secondary FeS minerals which co-precipitate or sorb arsenite as a likely mechanism of As immobilization, which was also supported by thermodynamic modeling of the pore water. Thus, sulfate additions can immobilize As and reduce its availability to rice plants in paddy soils containing a high potential for microbial Fe reduction, providing an efficient way to mitigate the As transfer to the food chain.

A two-compartment upflow pilot scale bioreactor system for microbial sulfate reduction control studies

Souring in oil fields occurs mainly due to the activity of sulfate reducing bacteria (SRB). Most of the studies on SRB are performed using upflow packed-bed reactors that have a limitation to describe the region close to the injection wells in oil fields, which is characterized by void and saturated porous bed regions. Here, it is described the design and operation of a pilot scale system to investigate the SRB activity, inhibition and control in oil fields.•The bioreactor is composed by two-compartments (empty and packed-bed).•The reactor system has two parallel bioreactors that can be supplied with the same source of nutrients through a single pump or can be supplied separately with different solutions using two pumps.•The hydrodynamics for conventional packed bed bioreactors has a mixing behavior dependent of the flow rate and has a significant by-pass. In contrast, the two-compartment system presented here has a mixing behavior almost independent of the flow rate.

Controlling the biocorrosion of sulfate-reducing bacteria (SRB) on carbon steel using ZnO/chitosan nanocomposite as an eco-friendly biocide

In this report, interlinked chitosan-ZnO nanocomposite at 10% ZnO (CZNC-10) is successfully used as green biocide for biofilm control and reduction of biocorrosion on carbon steel material. It was found that 250 μg/mL CZNC-10 can be used efficiently for the inhibition of sulfate reducing bacteria (SRB) biofilm on carbon steel. The Rct values after 21 and 28 days of incubation in presence of CZNC-10 are almost 3.2 and 2.8 times higher than the control respectively, indicating a strong corrosion inhibition with 74% as maximum inhibition efficiency.

Microbial Processes Mediating the Evolution of Methylarsine Gases from Dimethylarsenate in Paddy Soils.

Arsenic (As) biovolatilization is an important component of the global As biogeochemical cycle. Soils can emit various methylarsine gases, but the underlying microbial processes remain unclear. Here, we show that the addition of molybdate (Mo), an inhibitor of sulfate-reducing bacteria, greatly enhanced dimethylarsine evolution from dimethylarsenate [DMAs(V)] added to two paddy soils. Molybdate addition significantly affected the microbial community structure. The aerobic enrichment cultures from both soils volatilized substantial amounts of dimethylarsine from DMAs(V) in the presence of Mo, whereas the anaerobic enrichment cultures did not. A Bacillus strain (CZ-2) capable of reducing DMAs(V) to dimethylarsine was isolated from the aerobic enrichment culture, and its volatilization ability was enhanced by Mo. RNA-seq analysis identified 10 reductase genes upregulated by Mo. Addition of the reducing agent NADH increased dimethylarsine volatilization by strain CZ-2, suggesting that DMAs(V) reductase is an NADH-dependent enzyme. The strain could not methylate arsenite or convert monomethylarsenate and DMAs(V) to trimethylarsine. Our results show that dimethylarsine evolution from DMAs(V) is independent of the As methylation pathway and that Mo enhances dimethylarsine evolution from paddy soils by shifting the microbial community structure and enhancing the reduction of DMAs(V) to dimethylarsine, possibly through upregulating the expression of DMAs(V) reductase gene(s).

The Effectiveness of Nitrate-Mediated Control of the Oil Field Sulfur Cycle Depends on the Toluene Content of the Oil.

The injection of nitrate is one of the most commonly used technologies to impact the sulfur cycle in subsurface oil fields. Nitrate injection enhances the activity of nitrate-reducing bacteria, which produce nitrite inhibiting sulfate-reducing bacteria (SRB). Subsequent reduction of nitrate to di-nitrogen (N2) alleviates the inhibition of SRB by nitrite. It has been shown for the Medicine Hat Glauconitic C (MHGC) field, that alkylbenzenes especially toluene are important electron donors for the reduction of nitrate to nitrite and N2. However, the rate and extent of reduction of nitrate to nitrite and of nitrite to nitrogen have not been studied for multiple oil fields. Samples of light oil (PNG, CPM, and Tundra), light/heavy oil (Gryphon and Obigbo), and of heavy oil (MHGC) were collected from locations around the world. The maximum concentration of nitrate in the aqueous phase, which could be reduced in microcosms inoculated with MHGC produced water, increased with the toluene concentration in the oil phase. PNG, Gryphon, CPM, Obigbo, MHGC, and Tundra oils had 77, 17, 5.9, 4.0, 2.6, and 0.8 mM toluene, respectively. In incubations with 49 ml of aqueous phase and 1 ml of oil these were able to reduce 22.2, 12.3, 7.9, 4.6, 4.0, and 1.4 mM of nitrate, respectively. Nitrate reduced increased to 35 ± 4 mM upon amendment of all these oils with 570 mM toluene prior to incubation. Souring control by nitrate injection requires that the nitrate is directed toward oxidation of sulfide, not toluene. Hence, the success of nitrate injections will be inversely proportional to the toluene content of the oil. Oil composition is therefore an important determinant of the success of nitrate injection to control souring in a particular field.