Influence Of Sulfate-reducing Bacteria Research Articles

The influence of SRB on corrosion behavior of Cu-based medium-entropy alloy coating sprayed by HVOF

In this study, a novel Cu-based (Cu55Al20Ni12Ti8Si5, at.%) medium-entropy alloy (MEA) coating was prepared by high-velocity oxygen-fuel (HVOF) spraying technology. Thermo-Calc was employed to simulate the phase diagram of the alloy system. Phase composition and microstructure of the as-sprayed coating were characterized by means of XRD, FESEM, TEM and STEM/EDX. The effect of sulfate-reducing bacteria (SRB) on the corrosion behavior of the coating and the as-cast Ni-Al bronze (NAB) was investigated using electrochemical measurements and surface characterization. The Thermo-Cala simulation results showed that the alloy system presented a single BCC solid solution phase, while the detailed characterization of microstructure indicated that a few NiTi-rich B2-ordered precipitates could be also found in the as-sprayed coating other than the Cu-rich BCC matrix. Electrochemical studies illustrated that the coating exhibited superior corrosion resistance than the NAB in SRB medium, the corrosion acceleration efficiency induced by SRB of the NAB (95.3 %) was more severe than that of the coating (63.8 %). Surface analysis results demonstrated the occurrence of pitting corrosion and the formation of Cu2S on the coating surface after corroded in SRB medium. Corrosive metabolite HS- induced microbiologically influenced corrosion was considered as the main corrosion acceleration mechanism caused by SRB.

Influence of Sulfate-Reducing Bacteria on Corrosion Behavior of EQ70 High-Strength Steel

This work examines corrosion behavior of EQ70 high-strength steel under anaerobic conditions in artificial seawater containing sulfate-reducing bacteria (SRB). Polarization and electrochemical impedance spectra (EIS) tests were conducted. The results reveal that the corrosion rate initially decreased at the beginning of immersion. However, as the immersion time progressed, the corrosion rate of the high-strength steel increased, attributed to SRB reproduction. The scanning electron microscopy (SEM) results demonstrate that the corrosion was more severe in artificial seawater containing SRB compared to that of seawater without SRB. The morphologies of confocal laser scanning microscopy (CLSM) demonstrate that, after 15 days of immersion, the average depth of the corrosion pits on the sample in the artificial seawater containing SRB was nearly double that of the sample in the SRB-free seawater.

Influence of sulfate reducing bacteria cultured from the paddy soil on the solubility and redox behavior of Cd in a polymetallic system

As a toxic heavy metal, cadmium (Cd) easily enters into rice while rice grains greatly contribute to the dietary Cd intake in the populations consuming rice as a staple food. The availability of Cd in paddy soil determines the accumulation of grain Cd. Soil drainage leads to the remobilization of Cd, increasing bioavailability of Cd. In contrast, soil flooding results in little contribution of soil Cd to grain Cd, which is generally attributed to sulfate reduction induced by sulfate-reducing bacteria (SRB) in paddy soils. However, effects of SRB cultured from the paddy soil on the solubility and redox behavior of Cd have been seldom investigated before. Here, we used SRB enrichment cultures to investigate the temporal dynamics of Cd2+. The results showed that SRB enrichment cultures efficiently reduced solution redox potential (Eh) to less than −100 mV and gradually increased pH to neutral, demonstrating their ability to create a good anaerobic environment. The solubility of Cd obviously decreased in the anaerobic phase and Cd2+ was transformed into poorly dissolved CdS near the SRB cell wall edge. The addition of Zn2+ and/or Fe2+ further improved the decrease in Cd solubility and facilitated the formation of polymetallic sulfides as a consequence of promoting the production of S0 and dissolved sulfides (S2−/HS−) and the transformation of S0 into S2−/HS−. Little of Cd was detected in the media upon reoxidation, which was probably due to the high pH and the interaction between CdS and ZnS/FeS. Conclusively, these results demonstrate the detailed dynamic processes that explain the essential role of SRB in regulating the redox dynamics of chalcophile heavy metals and their bioavailability in paddy soils.

Influence of sulfate-reducing bacteria on the biocorrosion of mild steel coated with hybrid polyetherimide-ZnO or CuO bilayer composites

Mild steel (MS) coated with protective bilayer hybrid coatings of polyetherimide, and ZnO/CuO was exposed to artificial treated wastewater (ATWW) inoculated with Desulfovibrio sp. (biotic system). Proteins from the extracellular polymeric substances (EPS) matrix of Desulfovibrio sp. responded to the coatings. PEI-CuO offered the highest performance against biocorrosion. The higher PEI-CuO resistivity value of 2.17×10 6 Ω·cm 2 contrasted with the decrease to 1.5×10 5 and 1.6×10 3 Ω·cm 2 for PEI-ZnO and PEI coatings, respectively. The one order of magnitude increased resistance of the biotic system, compared to sterilized ATWW (abiotic system), resulted from the protective nature of the bacterial biofilm. Supplementary Materials: Supplementary material for this article is supplied as a separate file: crchim-227-suppl.pdf L’acier doux (MS) recouvert de revêtements hybrides bicouches protecteurs de polyétherimide et de ZnO/CuO a été exposé à des eaux usées artificielles (ATWW) inoculées par Desulfovibrio sp. (système biotique). Les protéines de la matrice des substances polymères extracellulaires (EPS) de Desulfovibrio sp. ont réagi aux revêtements. Le PEI-CuO a offert les meilleures performances contre la biocorrosion. La valeur de résistivité plus élevée de PEI-CuO de 2,17×10 6 Ω·cm 2 contraste avec la diminution à respectivement 1,5×10 5 et 1,6×10 3 Ω·cm 2 pour les revêtements PEI-ZnO et PEI. La résistance accrue d’un ordre de grandeur du système biotique, par rapport à l’ATWW stérilisé (système abiotique), résulte de la nature protectrice du biofilm bactérien. Compléments : Des compléments sont fournis pour cet article dans le fichier séparé : crchim-227-suppl.pdf

Effect of Sulfate-Reducing Bacteria (SRB) on the Corrosion of Buried Pipe Steel in Acidic Soil Solution

The influence of sulfate-reducing bacteria (SRB) on the corrosion behaviors of X80 pipeline steel was investigated in a soil environment by electrochemical techniques and surface analysis. It was found that SRB grew well in the acidic soil environment and further attached to the coupon surface, resulting in microbiologically influenced corrosion (MIC) of the steel. The corrosion process of X80 steel was significantly affected by the SRB biofilm on the steel surface. Steel corrosion was inhibited by the highly bioactive SRB biofilm at the early stage of the experiment, while SRB can accelerate the corrosion of steel at the later stage of the experiment. The steel surface suffered severe pitting corrosion in the SRB-containing soil solution.

Petrographic and rare earth elemental characteristics of Cambrian Girvanella oncoids exposed in the North China Platform: Constraints on forming mechanism, REE sources, and paleoenvironments

Oncoid-bearing Mioalingian strata in the North China Platform represent late highstand/forced regressive systems tract(s). In the current study, sequence stratigraphy, sedimentology, and microscopic studies were carried out to interpret the forming mechanism and paleoenvironment of these oncoids. Microscopic studies show the typical distribution of filamentous cyanobacteria (Girvanella) in the Cambrian oncoids. Based on these observations, the oncoids can be classified into three kinds, i.e., Girvanella-core oncoids, Girvanella-cortex oncoids, and Girvanella-full oncoids. Furthermore, the studied oncoids hold pyrite crystals and dolomite minerals that also indicate the influence of sulfate-reducing bacteria on their formation. The presence of Girvanella, pyrite, and dolomite in the cores and cortices of these distinctive oncoids depicts its microbial origin that flourished under relatively high-energy settings. The present work offers a reference example for the involvement of microbes, particularly Girvanella, in the development of microbial carbonates in the North China carbonate platform during the Cambrian period. Geochemistry of the Cambrian oncoids is interpreted in order to determine the involvement of detrital fractions, sources of rare earth elements (REEs), and paleoenvironmental settings. The results of slightly negative Eu anomalies, higher La/Yb (6.8–15.1), and the larger Y/Ho variations (30.17–42.08) in the studied oncoids advocate that these oncoids have been subjected to terrigenous input during their formation. Considering the absence of Ce anomaly, Gd/Gd* ratios (< 1), and lesser values of Y/Ho (30.17–33.93), we propose that these oncoids have been influenced by diagenetic activities. Relatively greater values of Er/Nd (0.09–0.23) suggest seawater signature preserved by the marine sediments. Meanwhile, observed weak negative Eu anomalies within the oncoids point out the retention of the original marine water characteristics, whereas lower values of the Y/Ho propose freshwater participation from the rivers in the seawater during precipitation of oncoids. Based on the ratios Er/Nd, (Nd/Yb)N, La/Yb, and depletion and variation of REEs, it can be confirmed that the sources of these REEs within the Cambrian oncoids are mainly from terrigenous input. However, the higher Er/Nd ratios are sourced from marine carbonates. Relatively lower values of Mo/U (1.10–2.46), V/Cr (< 2), V/(V + Ni) ratios (0.24–0.33), and deficiency of Ce anomaly in studied oncoids suggest their development under oxic environments. In addition, the variation of Sr/Cu (42–54) and Sr/Ba (35–79) indicates their growth under arid climatic conditions and classic marine settings. Considering these geochemical signatures, it can be concluded that the oncoids of the North China Platform flourished under oxic, arid, and classic marine conditions.

Воздействие сульфатовосстанавливающих бактерий на объекты нефтегазового комплекса и методы подавления их жизнедеятельности

Воздействие сульфатовосстанавливающих бактерий на объекты нефтегазового комплекса и методы подавления их жизнедеятельности

Influence of soil microorganisms on metal corrosion of underground pipelines

Abstract There have been revealed and summarized the regularities in biocorrosion of steel 17G1S-U, which is traditionally used for manufacturing oil and gas mains. The basic regularities of biocorrosion processes in the 17G1S-U pipe steel under the influence of SRB Desulfovibrio Sp. strains Kyiv-10 was obtained by weight-loss testing and surface analysis techniques. Effective inhibitors are proposed, which allow protecting steel 17G1S-U against the development of anaerobic corrosion under the influence of sulfate-reducing bacteria (SRB). The effectiveness of inhibitors is estimated by the degree of their protective effect. The porous structure of the surface film contributes to the initiation of localized corrosion. Damage analysis of the specimen surface corroded under different test conditions was performed.

Influence of sulfate-reducing bacteria on the corrosion behavior of 5052 aluminum alloy

Sulfate-reducing bacteria (SRB) are a major bacterial group involved in microbiologically influenced corrosion. The interaction between SRB and metals had been the focus of numerous investigations. In this paper, the interaction between SRB and 5052 aluminum alloy was studied using biological and electrochemical methods. Electrochemical analysis suggested that the corrosion rate of the aluminum alloy was accelerated substantially by SRB. This effect was based on the consumption of hydrogen, which in return promoted SRB metabolic activity. Deeper and larger micropits were found on alloy surfaces immersed in SRB. Energy dispersive spectroscopy analyses demonstrated that the concentration of Al on the surface of samples immersed with SRB was lower, while the concentrations of C, O, and S were higher than those without SRB. The results give an insight into clarifying the interaction between SRB and Al.

Influence of Sulfate-Reducing Bacteria on the Corrosion Behavior of High Strength Steel EQ70 under Cathodic Polarization.

Certain species of sulfate-reducing bacteria (SRB) use cathodes as electron donors for metabolism, and this electron transfer process may influence the proper protection potential choice for structures. The interaction between SRB and polarized electrodes had been the focus of numerous investigations. In this paper, the impact of cathodic protection (CP) on Desulfovibrio caledoniens metabolic activity and its influence on highs trength steel EQ70 were studied by bacterial analyses and electrochemical measurements. The results showed that EQ70 under -0.85 VSCE CP had a higher corrosion rate than that without CP, while EQ70 with -1.05 VSCE had a lower corrosion rate. The enhanced SRB metabolic activity at -0.85 VSCE was most probably caused by the direct electron transfer from the electrode polarized at -0.85 VSCE. This direct electron transfer pathway was unavailable in -1.05 VSCE. In addition, the application of cathodic protection led to the transformation of sulfide rusts into carbonates rusts. These observations have been employed to provide updated recommendations for the optimum CP potential for steel structures in the presence of SRB.

Influence of sulfate reducing bacteria on the cupronickel corrosion

Purpose – The purpose of this study is to explore the influence of the sulfate reducing bacteria (SRB) on the corrosion of cupronickel. Design/methodology/approach – Tests monitoring the change in free corrosion potential, linear polarization resistance and electrochemical impedance spectroscopy and examination using the scanning electron microscope and energy spectrum analysis were used to investigate the corrosion behavior of cupronickel in blank medium and in media inoculated with SRB to explore the influence of the SRB on the corrosion behavior of cupronickel alloy. Findings – The results show that SRB can destroy the surface oxide film of cupronickel and significantly reduce the free corrosion potential and polarization resistance of the cupronickel, causing the cupronickel to corrode significantly. Originality/value – SRB are widely found in the water supply system and is one of the important factors inducing microbial corrosion. This paper verified that SRB promote cupronickel corrosion and explored the influence and mechanism of attack.

Influence of Sulfate-Reducing Bacteria on the Corrosion Residual Strength of an AZ91D Magnesium Alloy.

In this paper, the corrosion residual strength of the AZ91D magnesium alloy in the presence of sulfate-reducing bacteria is studied. In the experiments, the chemical composition of corrosion film was analyzed by a scanning electron microscope with energy dispersive X-ray spectroscopy. In addition, a series of instruments, such as scanning electronic microscope, pH-meter and an AG-10TA materials test machine, were applied to test and record the morphology of the corrosion product, fracture texture and mechanical properties of the AZ91D magnesium alloy. The experiments show that the sulfate-reducing bacteria (SRB) play an important role in the corrosion process of the AZ91D magnesium alloy. Pitting corrosion was enhanced by sulfate-reducing bacteria. Corrosion pits are important defects that could lead to a significant stress concentration in the tensile process. As a result, sulfate-reducing bacteria influence the corrosion residual strength of the AZ91D magnesium alloy by accelerating pitting corrosion.

Corrosion behavior of carbon steel in presence of sulfate-reducing bacteria in seawater environment

• Carbon steel was exposed to sulfidogenic bacteria seeded seawater in a flow loop. • Localized surface attacks followed inoculations with sulfidogenic bacteria. • Bacteria activity does not necessarily lead to significantly elevated corrosion. • Complex corrosion deposits structure. • Antimicrobial treatment temporarily suppressed bacterial activity. The influence of sulfate-reducing bacteria (SRB) on the corrosion behavior of carbon steel was studied in a laboratory test-loop, continuously fed with nutrient supplemented North Sea seawater. The main parts of the test-loop, represented by two separated flow cells, were fitted with steel specimens. The test-loop was operating anoxically for 2200 h and each flow cell was three times inoculated with Desulfovibrio alaskensis or Desulfovibrio desulfuricans species. Additionally, each flow cell was two times perturbed with antimicrobial treatments. Steel specimens exposed in flow cells exhibited comparable appearance and systems responding similarly to inoculations and antimicrobial treatments. The effect of the inoculations in both flow cells on the steel coupons electrochemical behavior was materialized as lower resistance to corrosion and higher surface activity or occurrence of localized pitting events. The localized surface attacks recognized in both flow cells after inoculations continued to progress with the time, although bacterial activity was temporarily suppressed by antimicrobial treatment. Post-exposure sample evaluations might suggest that, some particular steel surface areas have been subjected to a dramatic change in the corrosion mechanism from initial localized attack to general corrosion. The long-term exposure of the carbon steel specimens resulted in identifiable formation of biofilms and corrosion products. Corrosion deposits were characterized by a specific structure built of iron sulfides (FeS), sulfated green rust (GR(SO 4 2− )), magnetite (Fe 3 O 4 ), Fe(III) oxyhydroxides (FeOOH), chukanovite (Fe 2 (OH) 2 CO 3 ), carbonated green rust (GR(CO 3 2− )) and some calcareous deposits. Presented factual evidence reinforced the idea that sulfidogenic species in natural seawater environment may cause localized damage with a specific surface pattern; however, this does not necessarily lead towards significantly elevated corrosion rates.

Influence of Sulfate-Reducing Bacteria on the Mobility of Arsenic in Soils an "In Vitro" Study

Ouro Preto/MG/Brazil soils are rich in arsenic containing minerals that once solubilized may contaminate water or food. Arsenic (As) is toxic if ingested or inhaled. Microorganisms and organic matter plays an important role in the dynamics of As in soils and sediments affecting its mobilization. Aims: to study the mobility of arsenic in the presence of organic matter and sulfur reducing bacteria (SRB) and also to obtain some As resistant bacterial cultures. Materials: Soil samples were collected from abandoned gold mines named Old Mine, Chico Rei and Santa Rita. As content in solid samples were in a range of 465 to 1829 mg Kg-1. Soil samples (5 g) were mixed with 35 ml of 2.5 M, CaCl2, stirred (5 min) and allowed to rest at 21.0°C for 1, 30, 60, 90 and 120 days. Other set of experiments were prepared following the previous procedure with some modifications: (i) group 1, flasks with bacterial inoculum (4 ml) from an enrichment of 5 g of soil and 45 ml of liquid medium B Postgate, pH 7.0, incubated at 35°C under anaerobic conditions; (ii) group 2, flasks with (5 g) of organic matter with As (III) adsorptive capacity (powdered chicken feathers - PCF), and (iii) group 3, flasks containing bacterial inoculum and organic matter. Results: As solubility was inversely proportional to time and depends on Fe and Mn contents. The influence of microorganisms on As immobilization was more relevant than the presence of organic matter. Surprisingly, in some cases, As solubility enhanced in the presence of PCF besides its As adsorptive capacity. One microbial consortium adapted to the culturing at pH 5.0 was obtained and this is an interesting feature considering the acid pH of the studied arsenic soils. Indigenous bacteria phenotypically similar to SRB may contribute to As immobilization in natural or impacted environment.

Influence of sulfate-reducing bacteria, sulfide and molybdate on hydrogen photoproduction by purple nonsulfur bacteria

The interaction between bacterial species is of great importance for H2 production using microbial consortia or non-sterile conditions. Sulfate reducing bacteria were found in anaerobic starch-hydrolyzing consortium and their inhibitory effect on the following H2 photoproduction by purple nonsulfur bacteria was shown. This inhibition was clearly demonstrated in the mixed culture of Rhodobacter sphaeroides and Desulfomicrobium baculatum using the synthetic medium. This effect was conditioned by sulfide production rather than H2 consumption or competition for organic substrate. Actually, the addition of equivalent sulfide concentration brought about the similar effects: inhibition of H2 production without growth inhibition, cells aggregation, and the increase of carbohydrate content as an alternative way of expenditure of organic acids. In the long-term experiments the average sulfide concentration of about 0.3 mM was detrimental while in short-terms the H2 production was not inhibited even at 3.2 mM. The protective effect of molybdates against sulfate reducers and sulfide was discussed.

Cathodic protection of XL 52 steel under the influence of sulfate reducing bacteria

AbstractThe effect of sulfate reducing bacteria (SRB) upon the cathodic protection of XL 52 steel was determined, in order to identify if the potential value of −0.950 V versus copper/copper sulfate electrode is good enough to protect the metal surface. During the experiments, different operational parameters were monitored: hydrogen sulfide production, iron concentration, electrolyte alkalinity, microorganisms' population, as well as the metal surface damage. At the same time, the corrosion rate was determined using two electrochemical techniques: polarization resistance (PR) and electrochemical impedance spectroscopy (EIS). According to the results, it was observed that the protection potential of −0.950 V versus copper/copper sulfate electrode is not enough to control the microbiologically induced corrosion. This situation is reinforced by the fact that significant iron concentration was found in the electrolyte. The microbiological activity is not affected by the protection potential. On the contrary, the population growth is slightly strengthened. The alkalinity generated by the applied potential did not stop the SRB growth. A type of localized corrosion was developed during the experiments with microorganisms, even when the protection potential was applied to the system.

Influence of sulphate-reducing bacteria on environmental parameters and marine corrosion behavior of Q235 steel in aerobic conditions

The growth cycle of sulphate-reducing bacteria (SRB), Desulfovibrio caledoniensis, and the effect of SRB on the environmental parameters and corrosion behavior of Q235 steel during a growth cycle in aerobic (air- and O 2-saturated culture solutions) and anaerobic (N 2 − saturated culture solutions) conditions were investigated. Oxygen dissolved in the culture solutions induced slow growth and fast decay of SRB. The growth process of SRB under anaerobic and aerobic conditions influenced sulphide anion concentration ( C s 2 − ) , pH, and conductivity ( κ). The values of C s 2 − and κ under aerobic conditions were lower than those under anaerobic conditions, and the pH values increased from O 2- to air- to N 2-saturated culture solutions. Aerobic conditions induced the open circuit potential ( E OC) to shift in the positive direction after the stationary phase of SRB growth. The charge transfer resistance ( R ct) increased quickly during the exponential growth phase, almost maintained stability during the stationary phase, and decreased after the stationary phase in all three conditions, and the impedance magnitude decreased from O 2- to air- to N 2-saturated culture solutions. The biofilms induced by SRB were observed by scanning electron microscopy (SEM) under aerobic and anaerobic conditions, and energy dispersive spectroscopy (EDS) was performed in abiotic and SRB-containing systems to distinguish the corrosion products. The reasons for the effects of SRB on the environmental parameters and corrosion behavior of carbon steel are discussed.

Control of Microbial Corrosion Using Coatings and Natural Additives

One of the major concerns in the oil and gas industry is corrosion. Microbial-influenced corrosion (MIC) can be defined as the deterioration of metals by natural processes directly or indirectly related to the activity of microorganisms. MIC affects many industries, such as petrochemical, ships and marine structures, power generating, aircraft fuel systems, waste water facilities, cooling water systems, process industries, paper mills, and water supply and distribution systems. In this study, the influence of sulfate-reducing bacteria (SRB), grown in a lactate/ sulfate culture medium, on the corrosion of both uncoated and coated mild steel was evaluated in the presence and absence of natural additives. To achieve this, an oilbased coating (alkyd) was used with and without the addition of natural additives to protect mild steel in a sulfate-reducing bacteria environment. Another objective of this study was to investigate the effects of SRB and/or their metabolites on the used coatings and the adverse effects of those coatings and additives on biofilm formation and bacteria growth rate. In this paper, 2 natural additives were identified for effective MIC protection. Natural products were selected based on the environmental appeal of the products. Two additives, derived from olive oil and Manhaden fish oil, were found to be effective in reducing MIC. In general, 2-3% of a natural additive was deemed adequate for effective MIC protection. Bacteria populations were counted at the beginning and at the end of the tests using the plate count method. After immersing the different coupons for 3 months in the SRB medium, it was noticed that the number of bacteria and their colonies were highly affected by both the environment and the used coating systems. A series of corrosion tests was performed to study the effectiveness of various natural additives. Visual observations, scanning electron microscopy (SEM) analyses, and computer image analyzer techniques were used to study the effects of SRB on the different coupon surfaces. It was observed that the presence of coatings inhibited both the biofilm growth and biocorrosion effects. The results revealed that the addition of some natural additives improved the protection ability of commercial coatings, with the best result with Manhaden fish oil.

Bacterial mitigation of pollutants in acid drainage using decomposable plant material and sludge

Effects of a clay-lime spiked sewage sludge and fresh decomposable ryegrass on the mitigation of an acid drainage were studied in the laboratory. Treatments (dry ameliorant weight/leachate ratio) were: (1) sludge (air-dried) at rates of 0, 8, 16 and 24%, (2) ryegrass at 0, 1, 1.5 and 2% (dry weight), (3) sludge (at the above-mentioned rates) and 1.5% ryegrass mixture. Measurements of mitigation (according to the criteria of changes in pH, Fe, S, Al and heavy metals) made every 10th day for 100 days showed ryegrass/sludge combination the most effective while sustaining mitigation longest, with or without the influence of sulphate-reducing bacteria (SRB). Sulphate and Fe in the acid drainage decreased in the order: sludge+ryegrass>sludge>ryegrass by 180, 40, 19; and 96, 83 and 54% respectively, compared with controls. An 11-fold decrease in soluble Al was caused by the highest rate of the combined sludge-ryegrass treatment but Al was doubled by the sludge-only treatment, and only minimally affected (2% reduction) by the ryegrass-only treatment. For the sludge plus ryegrass treatments at the highest rate of application, pH levels increased significantly, from 2.3 to >7 units and within 20 days of SRB activation, the concentration of Co, Cu, Mn, Ni and Zn decreased 3-, 15-, 90-, 3- and 50-fold respectively.

Influence of sulfate-reducing bacteria on outdoor hydrogen production by photosynthetic bacterium with seawater.

The application of seawater for bacterial fermentative production is a cost-effective technology. Hydrogen production by marine photosynthetic bacterium with seawater failed to continue after more than 10 days, and was accompanied by the formation of hydrogen sulfide and a change in culture color from red to black. However, substrate consumption in the blackish culture was comparable to that in a hydrogen-producing culture. A decrease in hydrogen production occurred upon the addition of sodium sulfide at concentrations of 1.5 mM or higher. PCR analysis targeted at the 16S rDNA sequence selective for sulfate-reducing bacteria revealed the existence of sulfate-reducing bacteria in inoculation cultures of the phototrophic bacterium and medium for hydrogen production. Hence, the high sulfate concentration of seawater, the low oxidation-reduction potential under hydrogen-producing conditions, and the presence of electron donors such as acetate might promote the metabolic activities of sulfate-reducing bacteria, resulting in the deterioration of hydrogen production with seawater.