Growth Of Sulfate-reducing Bacteria Research Articles

Experimental study on pipeline corrosion behavior coupled with microorganisms and dynamic alternating current interference

Underground pipelines buried deeper than 1.5 m or in specific soil conditions are susceptible to microbial corrosion and dynamic alternating current (AC) interference. Yet, research on the coupled effects of these factors remains limited, leaving their mechanisms unclear. The study employed microbial activity tests, electrochemical experiments, and microscopic morphology characterization to elucidate the coupled effect of sulfate-reducing bacteria (SRB) and dynamic AC interference on buried metallic pipelines. Results show that sinusoidal AC significantly reduces SRB growth activity. Initially, the active microbial film produced by microbial metabolism inhibited corrosion but later exacerbating it as the microbial film detachment. Microscopic examination reveals as the interference time increases, the corrosion morphology changed from pitting corrosion to honeycomb/ulcer shapes, under SRB and different AC interference conditions. Moreover, sulfide corrosion products and iron phosphide formation accelerate corrosion, while rectification and alternating electric field effects further aggravate the process. These findings provide insights into the complex mechanisms of microbial and AC corrosion in buried pipelines, aiding in anti-corrosion strategies and layout optimization.

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.

Study on the effectiveness of sulfate-reducing bacteria to remove Pb(II) and Zn(II) in tailings and acid mine drainage.

In view of water and soil getting polluted by Pb(II), Zn(II), and other heavy metals in tailings and acid mine drainage (AMD), we explored the removal effect of sulfate-reducing bacteria (SRB) on Pb(II), Zn(II), and other pollutants in solution and tailings based on the microbial treatment technology. We used the scanning electron microscope-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray fluorescence (XRF), to reveal the mechanism of SRB treatment of tailings. The results showed that SRB had a strong removal capacity for Zn(II) at 0-40 mg/L; however, Zn(II) at 60-100 mg/L inhibited the growth of SRB. Similarly, SRB exhibited a very strong ability to remove Pb(II) from the solution. At a Pb(II) concentration of 10-50 mg/L, its removal percentage by SRB was 100%. SRB treatment could effectively immobilize the pollutants leached from the tailings. With an increase in the amount of tailings added to each layer, the ability of SRB to treat the pollutants diminished. When 1 cm of tailingssand was added to each layer, SRB had the best effect on tailing sand treatment. After treatment, the immobilization rates of , Fe(III), Mn(II), Pb(II), Zn(II), Cu(II), and total Cr in the leachate of #1 tailing sand were 95.44%, 100%, 90.88%, 100%, 96.20%, 86.23%, and 93.34%, respectively. After the tailings were treated by SRB, although the tailings solidified into a cohesive mass from loose granular particles, their mechanical strength was <0.2 MPa. Desulfovibrio and Desulfohalotomaculum played the predominant roles in treating tailings by mixing SRB. The S2- and carbonate produced by mixing SRB during the treatment of tailings could metabolize sulfate by combining with the heavy metal ions released by the tailings to form FeS, MnS, ZnS, CuS, PbS, Cr2S3, CaCO3, MnCO3, and other precipitated particles. These particles were attached to the surface of the tailings, reducing the environmental pollution of the tailings in the water and soil around the mining area.

Occurrence of sulfate-reducing bacteria in well water: identification of anaerobic sulfidogenic bacterial enrichment cultures.

Bacteriological studies of well water mainly focus on aerobic and facultative aerobic coliform bacteria. However, the presence of obligate anaerobic bacteria in well water, especially sulfate-reducing bacteria (SRB), possible causative agents of some diseases, is often ignored. In this study, the presence of SRB and coexisting anaerobic bacteria with SRB in sulfate-reducing enrichment cultures obtained from 10 well water samples in Istanbul was investigated. A nested polymerase chain reaction-denaturing gradient gel electrophoresis strategy was performed to characterize the bacterial community structure of the enrichments. The most probable number method was used to determine SRB number. Out of 10, SRB growth was observed in only one (10%) enrichment culture and the SRB number was low (<10 cells/mL). Community members were identified as Desulfolutivibrio sulfodismutans and Anaerosinus sp. The results show that SRB coexist with Anaerosinus sp., and this may indicate poor water quality, posing a risk to public health. Furthermore, Anaerosinus sp., found in the human intestinal tract, may be used as an alternative anaerobic fecal indicator. It is worth noting that the detection of bacteria using molecular analyzes following enrichment culture techniques can bring new perspectives to determine the possible origin and presence of alternative microbial indicators in aquatic environments.

Assessment of rapid initiators and long-lasting nutrients for developing biological permeable reactive barriers to treat mine-contaminated groundwater

ABSTRACT The formation of mine-contaminated groundwater as a result of acidic mine drainage from the oxidation of sulfur-containing minerals entering the groundwater. Biological permeable reactive barrier (Bio-PRB) technology is excellent for the remediation of mine-contaminated groundwater. Usually, the organic substrates utilized in Bio-PRB are a combination of rapid initiators, which are readily bioavailable, and long-lasting nutrients, which are more difficult to degrade. Herein, we investigated the effectiveness of three rapid initiators and three long-lasting nutrients to remove sulfate from simulated mine-contaminated groundwater via simulated column experiments. The rapid initiators comprised crude glycerol, sodium acetate, and industrial syrup (IS), and the long-lasting nutrients included biodiesel emulsified oil, soybean oil emulsified oil, and high-carbon alcohol emulsified oil (HO). Microorganisms were stimulated using IS to create a sulfate reduction system owing to its high total organic carbon content (24.30 g L−1), achieving optimal sulfate removal rate (1.69 mmol dm−3 d−1). The fastest (2.93 mmol dm−3 d−1) and highest (88%) sulfate removal rates were achieved using HO, which is probably associated with the ability of HO to provide the most suitable C/N ratio (111.75) and induce the growth of sulfate-reducing bacteria (SRB) for substrate degradation. Conversely, a high concentration of sulfate reduction products inhibited SRB growth in the HO column. The addition of organic materials promoted SRB growth and various organic substrate–degrading bacteria. Furthermore, the competitive growth of methanogens (86.6%) may be responsible for the decrease in the relative abundance of SRB during the later stages of the experiment in the HO column.

Effect of coexistence of sulfate reducing bacteria and nitrate reducing bacteria on the under-deposit corrosion of carbon steel

The effect of sulfate reducing bacteria (SRB) and nitrate reducing bacteria (NRB) on under-deposit corrosion (UDC) of carbon steel is studied by weight loss tests, electrochemical measurements and surface analysis. The results show that SRB-induced UDC is significantly inhibited by NRB. This inhibition is attributed to the accumulation of NRB in deposits suppressing the growth of SRB, as revealed by the analysis of total accumulation number of bacteria and the characterization of bacteria-formed micro-holes indicating localized accumulation of bacteria in deposits. The suppressed SRB growth in deposits is discussed based on the NRB-induced biologically competitive exclusion and metabolite inhibition mechanisms.

Antibacterial and anticorrosion effects of Cetylpyridinium Chloride against Desulfovibrio desulfuricans biofilm and X80 steel corrosion

In this work, corrosion inhibition of X80 steel caused by Cetylpyridinium Chloride (CPC) in the presence of sulfate-reducing bacteria (SRB) was studied. The results showed that SRB accelerated the steel corrosion, whereas CPC had a good antibacterial activity against SRB corrosion. The growth of SRB was significantly inhibited with CPC concentration 10 mg L–1. The addition of 80 mg L–1 reduced the corrosion rate by 80 % in the presence of SRB. Molecular dynamics simulation and adsorption isotherm calculation showed that CPC can be adsorbed on the steel surface to form a protective film to protect steel form corrosion.

Corrosion of Q235 carbon steel induced by sulfate-reducing bacteria in groundwater: corrosion behavior, corrosion product, and microbial community structure.

Microbiologically influenced corrosion (MIC) is one of the reasons leading to the service failure of pipelines buried in the soil. In this work, the effect of sulfate-reducing bacteria (SRB) on the corrosion behavior of Q235 carbon steel in groundwater was investigated by electrochemical methods, surface analysis, and biological analysis. The results show that SRB utilizes iron as electron donor to sustain the vital activities of organic carbon-starved groundwater during the 14-day experimental period. The microbial community composition analysis at the genus level demonstrate that the diversity and richness decrease after corrosion, and the dominant SRB species has changed from Desulfovibrio to Desulfosporosinus. Moreover, the impedance of the carbon steel in the presence of biofilm was 1 order of magnitude higher than that of other periods in the electrochemical test, indicating that the biofilm and formed ferrous sulfide layer impeded the occurrence of corrosion. Although the 3D topography indicated that the surface of carbon steel was more uneven and pits were increased in the presence of SRB, the average weight loss (0.0396 ± 0.0050 g) was much higher than that without SRB (0.0139 ± 0.0007 g). These results implied that the growth of SRB makes the corrosion process of Q235 carbon steel more complicated.

Effects of Alcaligenes sp. on corrosion inhibition of sulfate-reducing bacteria in oilfield produced water

In this study, the effect of Alcaligenes sp. on the corrosion inhibition of sulfate-reducing bacteria (SRB) was evaluated and the mechanism was discussed from the aspects of Alcaligenes sp. metabolites, transform sulfide ability and the effect of corrosion product films. Alcaligenes sp. converted sulfides produced by SRB to S2O32-, which accumulated and converted to SO42-. The antimicrobial substances produced by Alcaligenes sp. inhibited the growth of SRB. The protein/polysaccharide had a certain corrosion inhibition effect and the corrosion product film was denser and more continuous. The combined effects of multiple factors inhibited the corrosion induced by SRB.

Effect of Acetate on Microbiologically Influenced Corrosion of Internal Pipeline Surfaces

Microbiologically influenced corrosion (MIC) is a serious threat to the integrity of crude oil pipelines. Sulphate-reducing bacteria (SRB) are the primary microorganisms responsible for MIC, and their aggressiveness is dependent on the energy source available to them. Acetate, a common energy source, has been shown to accelerate the corrosion of carbon steel in the presence of SRB. This study investigated the effect of acetate on the growth of SRB and the corrosion of carbon steel plates in simulated anaerobic conditions. The corrosion kinetics were studied using linear polarization resistance (LPR) and weight loss immersion tests for 42 days. The samples were characterized using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX). The results show that the addition of acetate to cultured media significantly increased the corrosion rate of carbon steel plates in both formation water and Postgate Medium B (PMB). This was due to increased growth of SRB in the presence of acetate, which led to the production of more corrosive hydrogen sulphide (H2S). The findings based on experimental data obtained from this study confirm that acetate can accelerate the corrosion of carbon steel in the presence of SRB.

Biosurfactant from a thermo-halophilic strain of Bacillus alveayuensis isolated from a Brazilian oil reservoir: Production, chemical characterization, antimicrobial activity, and efficiency in wettability reversal and oil removal from oil-soaked sand.

Biosurfactants (BS) are amphiphilic molecules from microbial secondary metabolism capable of reducing surface and interfacial tension between non-miscible phases, thus having a wide range of industrial and environmental applications. In this context, the present work aimed to study the biosurfactant produced by the bacterial strain Ar70C7-2, isolated from rocky samples of a deep offshore Brazilian oil reservoir, to evaluate its application in the oil industry. Its optimized production conditions, chemical structure, stability in extreme conditions, surface-active properties in porous media, and antibacterial action were evaluated. Strain Ar70C7-2 showed 100% similarity to Bacillus alveayuensis and was able to produce 0.27 g/L of crude BS in the Mineral Medium with glycerin and NH4NO3 at a ratio of 2, under fixed conditions of 70 g/L NaCl, incubation at 55 °C, and no stirring. The semi-purified BS presented emulsification index (E24) above 55%, surface tension of 31.8 mN/m, interfacial tension (against n-hexadecane) of 17.6 mN/m and CMC of 65 mg/L. The BS belongs to the class of lipopeptides, with a protein composition of 7% and fatty acid chain ranging from C14 to C18, with homologue C16 as the most abundant. Mass spectra of BS indicate the presence of surfactin, iturin, and fengycin families. Semi-purified BS was able to remove approximately 30% of the motor oil (10W40) present in oil-soaked sand, as tested by the contaminated sand washing method; it also promoted the alteration of carbonate wettability, as demonstrated in the flotation test and by the Washburn method. BS inhibited growth of the sulfate-reducing bacteria (SRB) Desulfovibrio marinus BRS-1 at concentrations of 2250 μg/mL and showed bactericidal action at concentrations of 2500 μg/mL. These results demonstrate that the biosurfactant produced by strain Ar70C7-2 has the potential for application in MEOR, bioremediation, and controlling SRB growth, encouraging further studies to validate its prospect in laboratory and field conditions.

Antibacterial Effect of Low-Concentration ZnO Nanoparticles on Sulfate-Reducing Bacteria under Visible Light.

The effect of ZnO nanoparticles (ZnO NPs), with different concentrations in simulated water, on the activity of sulfate-reducing bacteria (SRB) and their adhesion behaviour on stainless-steel surfaces, with and without visible light treatment, were investigated. The results showed that the concentration of ZnO NPs and light treatment greatly influenced the antibacterial performance of the NPs. In the water solution without light treatment, the low concentration (no more than 1 mg/L) of ZnO NPs in the aqueous solution promoted the growth of SRB, and the amount of biofilm attached to the stainless-steel surface increased. As the concentration increased, ZnO NPs exhibited antibacterial effects. In water under visible light irradiation, ZnO NPs showed antibacterial performance at all the concentrations studied (0.5~50 mg/L), and the antibacterial efficiency increased with the increase in the concentration of NPs. The determination results of the reactive oxygen species showed that light treatment can stimulate ZnO NPs in water to generate ·OH and O2·-, which exhibited good antibacterial properties. The adhesion amount of SRB on the stainless-steel surface was inversely proportional to the antibacterial efficiency of ZnO NPs.

Effects of cathodic protection potential on microbiologically induced corrosion behavior of X70 steel in a near-neutral pH solution

Sulfate reducing bacteria (SRB) are considered as one of the main causes for the failures of buried metal pipes. Although many researchers reported that more negative cathodic protection potential was required in environments containing SRB, SRB would increase the concentration of hydrogen adsorbed on steel surface and thus lead to hydrogen embrittlement. In the study, the optimum cathodic protection (CP) potentials of X70 steel in bacterial and sterile media were evaluated with electrochemical impedance spectroscopy. The morphology and composition of corrosion products were characterized by a scanning electron microscope (SEM), an energy dispersion x-ray spectrometer (EDS), and an x-ray photoelectron spectrometer (XPS). The corrosion morphology of X70 steel in NS4 medium was pits and the corrosion in the bacterial medium was more serious than that in the sterile medium. The corrosion products of X70 steel were FeOOH and Fe2O3 in the sterile medium, whereas its corrosion products in the bacterial medium were FeOOH and FeS. When CP potential was −775 mV, SRB growth was promoted and the optimal protection effect on X70 steel was achieved in the bacterial NS4 medium. Pits were still observed under the biofilm and the corresponding corrosion mechanism was extracellular electron transfer (EET). When CP potential was −875 mV, X70 steel realized the optimal protection in the sterile NS4 solution. However, CO2 hydrolysis and SRB metabolism in the bacterial medium resulted in hydrogen-induced pits. When CP potential was −1025 mV, the growth of SRB was inhibited and severe hydrogen evolution corrosion occurred on X70 steel in bacterial and sterile NS4 media. The optimal CP potential for pipeline steel in the sterile medium may lead to hydrogen corrosion in the bacterial medium when H+ concentration was high.

Experimental insights into the adsorption of newly synthesized Gemini ethoxylated surfactant on C-steel in different acidic media accompanied by DFT and MCs studies

Abstract Bis ethoxylated cationic surfactant (BOECS) is synthesized. The prepared surfactant’s structure configuration was verified through a variety of spectral and physicochemical techniques, including FT-IR, MS,1HNMR, and surface activity evaluations. BOECS applications as a C-steel corrosion inhibitor in 1.0 N HCl and 1.0 N H2SO4 and sulfate reducing bacteria (SRB) mitigations have been investigated thoroughly. Physical properties of the BOECS indicate its potential adsorption affinity at the air/water interface. The electrical conductivity determines the CMC value in accordance with the surface tension value. Electrochemical kinetic parameters indicate the BOECS is sorted as a mixed-type inhibitor and has an inhibition efficacy of 91.22 % and 81.26% for HCl and H2SO4, respectively. Active centers of BOECS structure enhance its adsorption at the electrolyte/C-steel. Calculated adsorption energy change (∆G ads) and theoretical adsorption energy (E ads) values suggest strong and spontaneous BOECS adsorption. The cytotoxic performance of the synthesized BOECS exhibited a potent inhibitory potential against the SRB. The outcomes of this research exhibit that the BOECS can lower SRB growth from 106 to 102 cell/mL.

Metagenomic insights into nutrient and hypoxic microbial communities at the macrofouling/steel interface leading to severe MIC

Adherent macrofouling in marine environments caused complex corrosion of steel surfaces, resulting in localized corrosion at the oyster/steel interface and uniform corrosion at the ascidian/steel interface. Sulfate-reducing bacteria (SRB) have been implicated in the microbiologically influenced corrosion (MIC) process at macrofouling-covered interfaces. To better understand the role of marine biofilms as key mediators in the MIC process, metagenomic techniques were used to study microbial communities and their response to macrofouling’s coverage. Compared to ascidians, the formed local anaerobic zone at oyster/steel interface stimulated the growth of SRBs, leading to higher FeS content and severe localized corrosion. SRB Desulfovibrio and Desulfobulbus, along with the SRB-related functional gene dsr, were found to increase, while oxygen-related function genes coxC, ccoN, ccoO, ccoP, and ccoQ decreased. In contrast, steel surfaces without macrofouling coverage had the richest microbial communities, yet experienced less severe MIC, suggesting no direct connection between microbial abundance/diversity and steel corrosion promotion.

Effect of phosphate on ferrihydrite transformation and the associated arsenic behavior mediated by sulfate-reducing bacterium

Although PO43- is commonly found in association with iron (oxyhydr)oxide, the effect of PO43- on ferrihydrite reduction, mineralogical transformation, and associated As behavior in sulfate-reducing bacteria (SRB)-rich environments remains unclear. In this study, batch experiments, together with geochemical, mineralogical, and biological analyses, were conducted to elucidate these processes. The results showed that SRB can reduce ferrihydrite via direct and indirect processes, and PO43- promoted ferrihydrite reduction by supporting SRB growth at low and medium PO43- loadings. However, at high loadings, PO43- stabilized the ferrihydrite. PO43- shifted the transformation of ferrihydrite from magnetite and mackinawite to vivianite, which scavenges As effectively by incorporating As into its particle. In systems with 0.5 mM SO42-, PO43- exerted a weak effect on As mobilization. However, in systems with 10 mM SO42-, substantial amounts of As were released into the solution, and PO43- impacted As behavior strongly. Low PO43- loadings increased the mobilization of As because of the competitive adsorption of PO43- on mackinawite. Medium and high PO43- loadings were beneficial for As immobilization because of the substitution of mackinawite by vivianite. These findings have important implications for understanding the biogeochemistry of iron (oxyhydr)oxide and As behavior in SRB-containing sediments.

Study on Growth Influencing Factors and Desulfurization Performance of Sulfate Reducing Bacteria Based on the Response Surface Methodology.

Sulfate reducing bacteria (SRB) can simultaneously and efficiently remove SO4 2- and heavy metal ions from acid mine drainage (AMD). Environmental factors have a great influence on AMD treated by SRB metabolic reducing sulfate. Providing a suitable growth environment can improve the effect of SRB on AMD. In this paper, the wet soil around the tailings reservoir was used as seed mud to enrich SRB. Based on the single factor experiment method and the response surface methodology (RSM), the effects of temperature, environmental pH value, S2- concentration, and COD/SO4 2- on the growth of SRB were analyzed. The effects of environmental factors such as temperature and pH on the desulfurization performance of SRB were investigated. The results showed that the growth curve of SRB was "S" type. SRB was in the logarithmic phase when cultured for 14-86 h, with high activity and vigorous growth metabolism. When the temperature is 32∼35 °C, the activity of SRB is the highest. With the gradual increase of the S2- concentration in the culture system, SRB activity will be inhibited and even lead to SRB cell death. The environmental pH value that SRB can tolerate is 5∼8, and when the environmental pH value is 7∼8, the SRB activity is the strongest. The chemical oxygen demand (COD)/SO4 2- that is most suitable for SRB growth is 2. The optimal growth conditions of SRB obtained from RSM were as follows: culture temperature at 34.74 °C, initial pH being 8.00, and initial COD/SO4 2- being 1.98. Under these conditions, the OD600 value was 1.45, the pH value was 9.37, the oxidation reduction potential (ORP) value was -399 mV, and the removal percentage of SO4 2- was 88.74%. The results of RSM showed that the effects of culture temperature, environmental pH, and COD/SO4 2- on the desulfurization performance of SRB were extremely significant. The order of affecting the removal of SO4 2- by SRB was environmental pH > temperature > COD/SO4 2-.

A diazotrophy-ammoniotrophy dual growth model for the sulfate reducing bacterium Desulfovibrio vulgaris var. Hildenborough

Sulfate reducing bacteria (SRB) comprise one of the few prokaryotic groups in which biological nitrogen fixation (BNF) is common. Recent studies have highlighted SRB roles in N cycling, particularly in oligotrophic coastal and benthic environments where they could contribute significantly to N input. Most studies of SRB have focused on sulfur cycling and SRB growth models have primarily aimed at understanding the effects of electron sources, with N usually provided as fixed-N (nitrate, ammonium). Mechanistic links between SRB nitrogen-fixing metabolism and growth are not well understood, particularly in environments where fixed-N fluctuates. Here, we investigate diazotrophic growth of the model sulfate reducer Desulfovibrio vulgaris var. Hildenborough under anaerobic heterotrophic conditions and contrasting N availabilities using a simple cellular model with dual ammoniotrophic and diazotrophic modes. The model was calibrated using batch culture experiments with varying initial ammonium concentrations (0–3000 µM) and acetylene reduction assays of BNF activity. The model confirmed the preferential usage of ammonium over BNF for growth and successfully reproduces experimental data, with notably clear bi-phasic growth curves showing an initial ammoniotrophic phase followed by onset of BNF. Our model enables quantification of the energetic cost of each N acquisition strategy and indicates the existence of a BNF-specific limiting phenomenon, not directly linked to micronutrient (Mo, Fe, Ni) concentrations, by-products (hydrogen, hydrogen sulfide), or fundamental model metabolic parameters (death rate, electron acceptor stoichiometry). By providing quantitative predictions of environment and metabolism, this study contributes to a better understanding of anaerobic heterotrophic diazotrophs in environments with fluctuating N conditions.

Versatile Medium for the Isolation of Sulfur-Reducing Bacteria from Natural Ecotypes

Sulfate-reducing bacteria (SRB) are a diverse group of microorganisms that are commonly isolated from anoxygenic environments (lake depths, soil, or swamps) and are also found in the intestines of humans and animals. They are well known for outcompeting methanogens for common substrates thereby helping in the decrease of methane emissions and also playing a major role in sulfur cycling. Therefore, determining the cultivable methods for their isolation is important. Various media has been used for the cultivation and purification of SRB from natural wetlands. The luxuriant growth of SRB was observed in all the media tested, out of which the best suitable media to recover a maximum of colonies from the natural soil/sediment samples was discovered as a modified postage medium. The enumeration of the isolated SRB was done by the most probable number (MPN) technique. A total of twenty pure isolates of SRB were isolated from different ecotypes.

Effect of Sulfate-Reducing Bacteria on the Production of Iron Sulfides

Using Fourier transform infrared spectroscopy (FTIR) to identify the sulfate-reducing bacteria (SRB) in Daqing Oilfield sewage. The growth curve of SRB and the adsorption ability of extracellular polymeric substances (EPS) to the Fe2+ were combined to explore iron sulfide generation. X-ray diffraction (XRD) results showed that different species of SRB produce iron sulfides, mainly composed of mackinawite. The growth characteristics of SRB affected the formation of iron sulfides and had a negative charge. Various SRB growth trends were different. The growth of the bacterium in an exponential phase or log phase can be described by the greater concentration of inoculation. And smooth growth trends were contributed to the formation of FeS. At the same time, sulfur-rich, like FeS2, was easily formed when S2− (or S2 2−) played a major role compared with the protein and polysaccharide functional groups in the negatively charged EPS at the process of Fe2+ adsorption.