Number Of Sulfate-reducing Bacteria Research Articles

Microbiological indicators of the biofilms microparticles of quartz sand and polypropylene after short-term exposure in soil

The purpose of this study was to investigate dynamics of biofilm biomass on microparticles of natural material quartz sand and the artificial material polypropylene (plastisphere) as well as change in biofilm-forming microorganisms’ number under a short-term in situ field study. In this study microparticles of polypropylene and quartz sand ranging in size from 3 to 5 mm were used. The total microbial count and the number of sulfate-reducing bacteria in the biofilm (by traditional culture-based microbiological methods) and the biofilm biomass (by the method with the crystal violet) were investigated. According to the determined microbiological indicators, over time (90 days) on the polypropylene it was observed decreasing of both the number of studied groups of microorganisms and the formation of a microbial biofilm, compared to the quartz sand. Determination of microbiological indicators of the materials surface allows understanding the aspects of their preservation/removal from the environment and requires additional research.

Amplicon-based sequencing revealed potential microbiologically influenced corrosion in the interim storage for spent fuel of RSG-GAS, Serpong, Indonesia

Abstract. Sugoro I, Fadila DSR, Pikoli MR, Hermanto FE, Ramadhan F, Shalsabilla SE, Cici A, Rijal MS, Rahayu DS, Puspito MJ, Haribowo DR, Tetriana D. 2023. Amplicon-based sequencing revealed potential microbiologically influenced corrosion in the interim storage for spent fuel of RSG-GAS, Serpong, Indonesia. Biodiversitas 24: 5391-5398. Interim storage of spent fuel (ISSF) corrosion can negatively impact nuclear power plant maintenance, specifically concerning safety, financial costs, and regulatory compliance. Besides chemical reactions, microbiologically influenced corrosion (MIC) also primarily occurred. Sulfate-reducing bacteria (SRB) plays a significant role in the development of MIC. The quantitative of MIC research has never been conducted in the ISSF - Multipurpose nuclear reactor of G.A. Siwabessy (RSG-GAS). So, this study aims to monitor the potential MIC development in the ISSF of RSG-GAS pool and canal through bacterial diversity analysis using total plate count (TPC) and metagenomic approach. TPC results showed that SRB was identified in the canal of ISSF but not in the pool site. However, metagenomics analysis revealed higher diversity measures in the pool than in the canal sites. Staphylococcus sp. was the most abundant species in both sites, with a relative abundance greater than 85%. The number of SRB and MIC-related bacteria was higher in the canal than in the pool, both from TPC and metagenomic analysis. Several SRB taxa were identified, such as Desulfobulbus mediterraneus, Desulfobulbus sp., Desulfofustis sp., Desulfovibrio sp., and Truepera sp. The potential MIC development also strengthens by diversity-based metabolic pathway prediction, which mainly displayed sulfur oxidation and sulfate reduction pathways in the canal system.

Corrosion Behavior on 20# Pipeline Steel by Sulfate-Reducing Bacteria in Simulated NaCl Alkali/Surfactant/Polymer Produced Solution.

The corrosion behavior of sulfate-reducing bacteria (SRB) on 20# carbon steel in the NaCl alkali-surfactant-polymer (ASP) flooding system was studied by scanning electron microscopy, electrochemical measurement, X-ray photoelectron spectroscopy, and laser confocal microscopy. The results showed that the presence of SRB results in a large viscosity loss of the system. SRB can use hydrolyzed polyacrylamide (HPAM) as a nutrient to grow, and the number of SRB remained at a high level after 15 days. Weight loss and electrochemical tests indicated that SRB promoted corrosion of pipeline steel. The corrosion of carbon steel in the early stage of immersion was inhibited by the biofilm formed on the surface, and the thick biofilm in the later stage of immersion caused serious pitting corrosion. The localized corrosion caused by SRB was not inhibited by HPAM and sodium petroleum sulfonate (surfactant) adsorbed on the surface.

Biological fouling and corrosion resistance of Ni-based coating on AH32

ABSTRACT To reduce the destruction of organic biological fouling in marine steel, nickel-based (NiCrAlY) transition coatings with and without silver (Ag) doping were prepared on AH32 marine steel by plasma spraying. The coatings exhibited a layered structure, and AlNi3 (111), (200), and (220) diffraction peaks were detected. The Ag (111) peaks were also observed for the Ag-doped coatings. The number of sulphate-reducing bacteria (SRB) adsorbed on the coating surfaces reduced after immersion in the bacterial solution, and their shells were disintegrated because of the presence of Ag. The corrosion potentials of AH32, NiCrAlY, and NiCrAlY(Ag) coated AH32 plates were nearly identical at approximately −720 mV. After being covered with organic paint, the corrosion potential and current density of the NiCrAlY(Ag) coating increased to −624 mV and decreased by one order of 2.75 × 10− 6 A cm−2, respectively. The NiCrAlY(Ag) coating effectively inhibited biological fouling.

Improvement in the microbially induced corrosion resistance of concrete sewers using electrodeposition

In this study, Cu2O/CuO and Cu were electrodeposited onto a mortar surface to protect concrete sewers from microbially induced corrosion. The effects of temperature and electrolyte pH on the antimicrobial performance of the electrodeposited specimens were investigated through surface analysis and measurements of bacteria inhibition rate during the exposure to Desulfovibrio desulfuricans and Acidithiobacillus thiooxidans. Variations in the number of sulphate-reducing bacteria (SRB) cells were determined directly using haemocytometer, and sulphate concentration and pH of sulphate-oxidizing bacteria (SOB) medium were measured to evaluate the bactericidal property against SOB. Results demonstrate that all the electrodepositited specimens exhibited a favourable bactericidal performance. In addition, a short-term simulated microbially induced corrosion experiment running for 30 days was conducted. Visual, physical and ions leaching investigations of mortar samples were performed to estimate the durability. Considering the integrity of the coated surface, bactericidal property, the leaching rate of Cu2+ ions, and permeability of the treated specimens, 60 °C and pH 11 were determined to be the optimum conditions for electrodeposition.

Influence of anion and sulfate-reducing bacteria on the stress corrosion behavior and mechanism of X70 steel in a marine mud environment

Subsea pipeline steel was severely corroded due to the presence of huge quantities of Cl-, SO42-, and sulfate-reducing bacteria (SRB) in marine mud. In this paper, the synergistic effects of Cl-, SO42- and SRB on the stress corrosion cracking (SCC) behavior of X70 steel in a simulated solution of marine mud in the South China Sea were examined using slow strain rate tensile (SSRT) tests, surface morphology analysis, and combined electrochemical experiments. The results indicated that the sensitivity of the specimens to stress corrosion increased as the concentration of Cl- rose. Cl- not only encouraged pitting and intensified the corrosion autocatalytic process but also influenced the number of surviving SRB. At a concentration of 20 g/L, the greatest number of SRB survived in the present investigation. However, when the Cl- concentration was 30 g/L, the anodic dissolution rate was the quickest and the SCC sensitivity was the highest, due to the synergistic impact of the high Cl- concentration and SRB. SO42- functions as an electron acceptor for SRB in the electrochemical reaction process and influences the adsorption of Cl-. Its rising concentration sped up the anodic dissolving process and increased the sensitivity of SCC.

Identification of microbes isolated with test kits through culture-dependent and metabarcoding techniques for assessment of microbial corrosion

• The diversity of microbes in biofilms/orange tubercles was narrowed through the use of various test kits. • Metabarcoding of enriched biomass confirmed the kits’ selection of microbial phenotypes. • Kit enrichment is useful for isolating specific bacteria for biocorrosion studies. Commercial diagnostic test kits are often used to confirm the presence of specific microbes associated with microbially influenced corrosion (MIC). We evaluated two of these kits in detail to assess their applications, by using biofilm/tubercle samples from a marine steel wall in a southern Australian harbour. The studied biofilms included different layers of orange tubercles (typically associated with accelerated low water corrosion (ALWC), with or without underlying pitting) and non-orange coloured (without underlying corrosion) biofilms. Two kit brands were used to assay sulfate reducing bacteria (SRB), acid producing bacteria and/or iron related bacteria. Significantly different microbial communities were revealed by the two kits. MIC/ALWC have often been attributed to SRB; however, the SRB kit results did not support such a relationship. The SRB abundance determined with both kits was higher in outer orange tubercles than inner orange tubercles (where any aggressive corrosion would have occurred). The non-orange biofilm, in contrast to the orange tubercles, generally had the highest numbers of SRB. We explored the microbes enriched by the test kits through preliminary pure culture isolation and 16S rRNA metabarcoding. Some microbes identified through kit enrichment were likely to have had the properties that the test kits were designed to detect, but several identified microbes did not have the target phenotype.

The influence of carbon steel chemical composition on the biochemical activity of sessile sulfate-reducing bacteria

The technogenic failure caused by biological corrosion of pipelines and other oilfield equipment is an urgent problem for all oil-producing countries of the world. It has been established that many types of corrosion are initiated by the development of sulfate-reducing bacteria on the inner pipe surfaces. This paper presents the results of model laboratory experiments aimed at assessing the effect of the chemical composition of pipeline steel on the number and biochemical activity of sulfate-reducing bacteria development on its surface. Three chromium-containing corrosion-resistant steels were selected for the experiment, steel samples alloyed with 1% manganese were used as control samples. The bacteria for model experiments, mostly belonging to the genus Desulfovibrio, were taken from the inner surface of the damaged pipe after exploitation at an oil field in the Samara Region. In model experiments a reliable influence of the chemical composition of pipe steel on the quantitative characteristics and biochemical activity of bacteria developing on its surface was established. The biochemical activity of sulfate-reducing bacteria, determined by the stimulation of hydrogen sulfide formation and a change in dehydrogenase activity, significantly depended on the chromium content. An increase in the chromium concentration in the tested steel samples by up to 5% reduced the number of sulfate-reducing bacteria and their biochemical activity. The experiments allow us only to make a conclusion about the influence of the chemical composition of pipe steels on the number and biochemical activity of sulfate-reducing bacteria, but do not reveal its resistance to bacterial corrosion.

Insights into how poly aluminum chloride and poly ferric sulfate affect methane production from anaerobic digestion of waste activated sludge

Poly aluminum chloride (PAC) and poly ferric sulfate (PFS) are widely used in wastewater treatment and sludge dewatering, resulting in their amounts being accumulated substantially in waste activated sludge (WAS). Till now, however, little information about their influence on WAS digestion is available. This work therefore aims to provide insights into how PAC and PFS affect sludge anaerobic digestion. The experimental results showed that PFS's inhibition to methane production was much severer than PAC, in control reactor (0 mg Al or Fe /g TSS), the maximum cumulative methane production was 152.99 ± 7.18 mL/g VSS, when flocculants concentration increased to 30 mg Al/g TSS or 30 mg Fe/g TSS, the yields decreased to 129.54 ± 6.18 mL/g VSS and 89.52 ± 4.82 mL/g VSS respectively. Mechanism explorations exhibited that protein in WAS could bond with flocculants, which would inhibit protein bioconversion. It was also observed that the apparent activation energy (AAE) of organic solubilisation of PAC and PFS-contained sludge were increased by 38.58% and 18.67% respectively. Meanwhile, compared to the PFS, PAC led to more serious suppression of hydrolysis and acidogenesis processes, with propionic acid used as substrate, PFS inhibit methanogenesis more severely than PAC. Illumina MiSeq sequencing analyses showed that the number of sulfate-reducing bacteria (SRB) enriched obviously in PFS reactor. The results revealed that although PFS reduced methane production more severely than PAC, the reduction was mainly enforced by the activity of SRB but not organic enmeshment. Furthermore, PAC severely suppresses acetotrophic methanogens but PFS depress hydrogenotrophic methanogenesis microorganism mainly. Additionally, malodor control and dewaterability enhancement of digested sludge can be realized with PAC existence. The finding obtained in this study would provide insights into the PFS or PAC-involved sludge anaerobic digestion system and might support the important implication for further manipulate WAS treatment in the future.

Biological sulfate removal with low-cost carbon sources using cold-acclimated bacteria

Abstract The main goal of this study was to develop a cost-efficient biological method for the removal of sulfate from mining effluents in cold conditions. A consortium of cold-tolerant sulfate-reducing bacteria (SRB) was tested at 6 °C regarding the utilization of economically viable, low-cost carbon sources, i.e., whey, conditioned sewage sludge, and peat, in the removal of sulfate from synthetic mining water. Succinate was used as a reference carbon source. Of all the studied low-cost carbon sources, conditioned sewage sludge proved to be the most efficient. Nuclear magnetic resonance (NMR) spectroscopy revealed that sewage sludge contained propionic acid, which proved to be utilizable by SRB under cold conditions. Peat both adsorbed the sulfate and acted as a nutrient source in the sulfate reduction process. When whey was used as a carbon source, only a slight decrease in sulfate concentration was detected. Succinate was found to work in a truly predictable and efficient way as a carbon source in biological sulfate reduction, even at the lowest concentration tested. The use of conditioned sewage sludge increased the bacterial diversity in liquid cultivations significantly. However, the number of SRB was highest in the succinate cultivations.

Sulfate removal performance and co-occurrence patterns of microbial community in constructed wetlands treating saline wastewater

The migration and transformation of sulfur is closely related to carbon sources. However, knowledge on the co-occurrence patterns of sulfur-related bacteria and other carbon-consuming microorganisms in constructed wetlands (CWs) is limited. In this study, CWs with intertidal wetland sediments (IWS), as microbial inoculant, was constructed to investigate the sulfate and chemical oxygen demand (COD) removal rates, microbial community composition, and co-occurrence network. IWS-enhanced CWs planted with Phragmites australis (PA+) and unplanted ones (CT+) were set up with controls (PA and CT). Results showed that the sulfate removal rate was higher in PA+ (60.60% ± 0.80%) than PA (44.64% ± 2.72%). The sulfate removal rate decreased and that of COD increased in PA+ and PA when the influent sulfate concentrations were raised. Microbial analysis indicated that the numbers of sulfate-reducing bacteria (SRB), sulfur oxidizing bacteria (SOB), and carbon-degrading bacteria improved the removal efficiency of sulfate in PA+ and CT+. The microbial topological pattern revealed that the exchange of matter, energy, and information by microorganisms in PA+ and CT+ was faster than that in PA and CT. The co-occurrence network analysis indicated that SRB (e.g., unclassified Desulfuromonadaceae) harbored negative correlations with denitrifying bacteria (e.g., Thauera, Flavobacterium, and unclassified Burkholderiaceae) because of electron donor competition. However, Flavobacterium and Thauera could cooperate to denitrify through different electron donors to avoid competition. Moreover, Pseudomonas and Amaricoccus had cross-feeding and cooperation in the network when carbon was restricted.

Comparison of retention and output of sulfur in limestone soil and yellow soil and their responses to acid deposition in a small karst catchment of Guizhou Province, Southwest China.

Investigating the responses of retention and output of sulfur (S) is significant to understand the impact of atmospheric S deposition on the S cycling in soils and its environmental effects in the karst catchments of Southwest China. This study analyzed the contents and δ34S values of different S forms (total S, carbon-bonded S, ester-bonded SO42-, SO42-, and total reduced inorganic sulfur [TRIS]), the δ34S values of stream SO42-, the δ13C values of soil organic carbon, and sulfate-reducing bacteria (SRB) quantity in limestone soil and yellow soil profiles in a typical small karst catchment of Southwest China. The results showed that under the same acid deposition level, the limestone soil and yellow soil profiles are significantly different from the distribution of contents and δ34S values of different S forms and the number of SRB. At the same time, more than 70% of the SO42- in the stream water draining the sampling slopes came from soils at different depths in limestone soil and yellow soil profiles. These results indicate the different response of retention and output of S in the limestone soil and yellow soil to S deposition input. The organic S formation and dissimilatory SO42- reduction (DSR) to form TRIS are S retention processes that exist in both limestone soil and yellow soil profiles. There are processes of transport and accumulation of SO42- at the bottom layer in yellow soil profile; therefore, retaining S as absorbed SO42- is also a main S retention process in yellow soil. At present, the output of SO42- through stream water mainly comes from the deposited SO42- which undergoes DSR reaction driven by SRB, not from organic S mineralization and desorption of adsorbed SO42- in the limestone soil and yellow soil profiles. However, organic S is the main S form in limestone soil and yellow soil. After the annual S deposition flux is significantly reduced, organic S mineralization in limestone soil and yellow soil profiles may release a large amount of SO42- into the surface water.

Universalism of inhibitors against hydrogen sulfide and carbon dioxide corrosion of carbon steel

The universality of inhibitors is understood as their ability to inhibit several types of corrosion attack: hydrogen sulfide and carbon dioxide corrosion, hydrogen diffusion into metal, development of sulfate-reducing and other types of bacteria, negative impact on the mechanical properties of metals. Indicators of universalism of new inhibitor have been studied. Producer of the inhibiting compositions is Limited Liability Company «INCORGAZ» (S-Petersburg, Russia). The efficacy of the inhibitor in the concentration of 25 - 200 mg/L has been studied with respect to carbon steel in a highly mineralized chloride medium (pH= 6) and NACE medium (5 g/L NaCl, 0.25 g/L CH3COOH, pH =3.5) containing H2S (50-400 mg/L) and CO2 (1at) separately and together. The bactericidal properties of the inhibitor were studied with respect to sulfate-reducing bacteria in the Postgate medium. The investigations were carried out by the methods of linear polarization resistance, electrochemical impedance spectroscopy, gravimetry, potentiodynamic polarization. The protective effectiveness of the inhibitor reaches 80% in the presence of CO2 and 90% in hydrogen sulphide environments. The inhibitor repeatedly reduces the number of sulfate-reducing bacteria and the production of biogenic hydrogen sulfide and inhibits the diffusion of hydrogen into steel.

Greywater: Understanding biofilm bacteria succession, pollutant removal and low sulfide generation in small diameter gravity sewers

Separate collection of greywater by small diameter gravity sewers (SDGS) has been widely used to achieve greywater treatment and recycling. Bacteria in SDGS biofilms might have the ability to pretreat pollutant and generate sulfide causing impacts on sewer operation. In this study, SDGS reactors coupled with quantitative polymerase chain reactions and Illumina sequencing were operated for ninety days to study the bacterial characteristics and pollutant removal ability. Results indicated that biofilm thickness (mainly 1040–2120 μm), bacterial count (approximately 4 × 108 cells/cm2), bacterial communities, and functional bacteria distribution changed regularly in the greywater SDGS biofilms. Proteobacteria (60.39 ± 12.31%) and Bacteroidetes (26.22 ± 13.94%) were the predominant phyla in the SDGS biofilms, while Pseudomonas (14.47 ± 6.59%) and Enterobacter (6.01 ± 2.01%) abundance were relatively stable. Sulfate-reducing bacteria (SRB) and denitrifying bacteria inhabited the greywater SDGS biofilms and the number of SRB was not dependent on the dissolved oxygen concentration but had a linear relationship with biofilm thickness. Greywater SDGS showed the ability to decrease the chemical oxygen demand stably during the study but its removal of nitrogen and phosphorus was indeterminate. This research established that the low sulfide concentrations generated by greywater SDGS (<0.08 mg L−1·km−1) make these systems beneficial for sewer operation and maintenance. The main novelty of this study is the in-depth analysis of the bacterial community and pollutant removal in greywater SDGS and the confirmation of low sulfide generation in greywater SDGS which is beneficial for the sustainable development of sewer systems.

Diversity and community pattern of sulfate-reducing bacteria in piglet gut

BackgroundAmong the gut microbiota, sulfate-reducing bacteria (SRB) is a kind of hydrogen-utilizing functional bacteria that plays an important role in intestinal hydrogen and sulfur metabolism. However, information is lacking regarding diversity and community structure of SRB in the gut of piglets. Middle cecum contents were collected from 6 Yorkshire and 6 Meishan piglets at postnatal days (PND) 14, 28 and 49. Piglets were weaned at PND28. Real-time quantitative PCR was performed to detect the number of SRB in the cecum based on dissimilatory sulfite reductase subunit A (dsrA) gene. Prior to real-time PCR, plasmid containing the dsrA gene was constructed and used as external standard to create a standard curve, from which the gene copies of dsrA were calculated. H2S concentration in the cecal contents was measured. Illumina PE250 sequencing of dsrA gene was used to investigate SRB diversity in cecum contents.ResultsThe qPCR results showed that the number of SRB at PND49 was significantly higher than that at PND28 in Meishan piglets. The concentration of H2S has no significant difference between piglet breeds and between different ages. The Illumina sequencing analysis revealed that the Chao1 richness index was significantly higher at PND49 than that at PND14 and PND28 in Yorkshire piglets. Based on dsrA gene similarities, Proteobacteria, Actinobacteria, and Firmicutes were identified at the phylum level, and most sequences were classified as Proteobacteria. At the genus level, most of sequences were classified as Desulfovibrio. At the species level, Desulfovibrio intestinalis was the predominant SRB in the piglet cecum. The relative abundance and the inferred absolute abundance of Faecalibacterium prausnitzii at PND49 were significantly higher than that at PND14 in Yorkshire piglets. Pig breeds did not affect the dsrA gene copies of SRB, diversity index and community pattern of SRB.ConclusionsSulfate-reducing bacteria are widely colonized in the cecum of piglets and D. intestinalis is the dominant SRB. The age of piglets, but not the pig breeds affects the diversity and community pattern of SRB.

Analysis of cultivable aerobic bacterial community composition and screening for facultative sulfate-reducing bacteria in marine corrosive steel

Anaerobic, aerobic, and facultative bacteria are all present in corrosive environments. However, as previous studies to address corrosion in the marine environment have largely focused on anaerobic bacteria, limited attention has been paid to the composition and function of aerobic and facultative bacteria in this process. For analysis in this study, ten samples were collected from rust layers on steel plates that had been immersed in seawater for different periods (i.e., six months and eight years) at Sanya and Xiamen, China. The cultivable aerobic bacterial community structure as well as the number of sulfate-reducing bacteria (SRB) were analyzed in both cases, while the proportion of facultative SRB among the isolated aerobic bacteria in each sample was also evaluated using a novel approach. Bacterial abundance results show that the proportions are related to sea location and immersion time; abundances of culturable aerobic bacteria (CAB) and SRB from Sanya were greater in most corrosion samples than those from Xiamen, and abundances of both bacterial groups were greater in samples immersed for six months than for eight years. A total of 213 isolates were obtained from all samples in terms of CAB community composition, and a phylogenetic analysis revealed that the taxa comprised four phyla and 31 genera. Bacterial species composition is related to marine location; the results show that Firmicutes and Proteobacteria were the dominant phyla, accounting for 98.13% of the total, while Bacillus and Vibrio were the dominant genera, accounting for 53.06% of the total. An additional six facultative SRB strains were also screened from the isolates obtained and were found to encompass the genus Vibrio (four strains), Staphylococcus (one strain), and Photobacterium (one strain). It is noteworthy that mentions of Photobacterium species have so far been absent from the literature, both in terms of its membership of the SRB group and its relationship to corrosion.

Response of bentonite microbial communities to stresses relevant to geodisposal of radioactive waste

Microbes have been isolated previously from bentonite materials that may be used as barriers for the disposal of radioactive waste. Actively respiring microbes in such barrier materials, within a repository environment, have the potential to adversely affect waste container corrosion rates. Additionally, they could potentially alter the properties of the bentonite barrier itself. This is of significance, since the integrity of the waste container and properties of the bentonite barrier are required to fulfil defined safety functions. To help identify the critical factors that affect microbial activity in bentonite materials, this study examines the impact of a range of parameters that could affect microbial metabolism in a geodisposal environment. Several bentonites from different sources (bentonite mined from locations in Spain and the USA, along with commercially-sourced bentonite) were subjected to increased pressure (74 MPa, 30 s), heat (90 °C, 24 h), and irradiation (1000 Gy, 24.17 Gy min−1), before incubation in growth media selective for sulfate-reducing bacteria (SRB) or iron-reducing bacteria (IRB). The amount of SRB, and IRB were counted using the most probable number method and identified by 16S rRNA gene sequencing. The bentonites initially contained 660–6600 SRB cells g−1, and the number of SRB was correlated with the initial water content of the bentonite. A similar number of IRB was also present (400–4000 cells g−1), and the number of IRB was correlated with the ratio of bioavailable Fe(II)/Fe(III) present in the bentonite. The bentonites hosted sulfate-reducing species from two bacterial genera, with Desulfotomaculum dominating the SRB communities in the Spanish bentonite used in the Full-scale Engineered Barriers Experiment (FEBEX), while the other communities contained Desulfosporosinus species. The nature of the SRB community played a significant role in the microbial community response to different stresses, with the FEBEX material producing high SRB cell counts in response to pressure and irradiation but yielding low numbers in response to heat. Initially, the IRB communities contained a mixture of Gram-negative bacteria such as Geobacter, and Gram-positive spore-forming bacteria such as Bacillus and Desulfosporosinus, with an increase in the number of Gram-positive spore-formers in response to stress. The ability of Gram-positive spore-formers to grow, despite exposure to pressure, heat and irradiation, highlights the need to generate a swelling pressure sufficient to minimise microbial activity. In addition, we suggest that the microbial communities naturally present in the bentonite should be considered as part of the selection process for buffer materials in a geological disposal facility for radioactive waste.

CORRELATION BETWEEN BIOMASS CONCENTRATION AND EXTENT OF SULPHATE REDUCTION IN AN ACIDOGENIC REACTOR

Two stage high rate anaerobic treatment systems comprising of an acidogenic reactor (or equalisation/ buffer tank) followed by a methanogenic reactor are becoming increasingly popular to treat high strength wastewater from industries. In these systems, sulphate present in the wastewater is reduced to sulphide either partially or completely in the acidogenic reactor and completely in the methanogenic reactor. The effect of fermentation products on the extent of sulphate reduction in the acidogenic reactor was investigated in a continuously-fed, well mixed laboratory-scale 3 L fermenter operating at a temperature of 35oC and pH of 6. The feed was based on either glucose or molasses as the carbon source. It was observed that as the carbohydrate concentration in feed was increased sulphate reduction was suppressed. It was confirmed that volatile organic acids like acetic, propionic and butyric acids, hydrogen and residual glucose did not cause inhibition of sulphate reduction. However, biomass concentration correlated negatively with extent of sulphate reduction. This correlation was expressed mathematically and the same expression with the same parameters adequately predicted the effect of biomass concentration on extent of sulphate removal for both steady state and transient data irrespective of glucose or molasses feed. It was seen from the best fit of this expression that a biomass concentration of 3300 mg-COD.L-1 would completely repress sulphate reduction in the acidogenic reactor. Even when sulphate removal was suppressed the presence of sulphate reducing bacteria (SRB) in the reactor was confirmed through Fluorescent In Situ Hybridisation (FISH) visualisation. Moreover, the numbers of SRB seemed to increase with carbohydrate concentration in feed. It was speculated the suppression of sulphate removal might be due to a switch in function of SRB from sulphate reducing to fermentation or acetogenesis. Keywords: sulphate reducing bacteria, anaerobic digestion, inhibition, sulphate reduction, acidogenic reactor, high rate anaerobic treatment

Effects of Microbial Activities on Mercury Methylation in Farmland near Mercury Mining Area

In order to study the main effect of microbial activities on mercury(Hg) methylation in farmland, mercury contaminated upland soils and paddy soils near Hg mining area were sampled as experimental soils. Four treatments were designed including only sterilization as the control, accelerating the activities of sulfate reducing bacteria(SRB), inhibiting the SRB's activities, and accelerating the activities of iron-reducing bacteria(FeRB), to know the effects of microbial and non-microbial factors on mercury methylation in soils. The results were as follows:the highest concentration of methylmercury(MeHg) was observed in soils with SRB accelerated treatment, and the increments of MeHg concentrations in upland soils and paddy soils ranged from 0.15 μg·kg-1 to 0.38 μg·kg-1 and 1 μg·kg-1 to 2 μg·kg-1, respectively. Comparatively, little increments of MeHg concentration were seen in soils with SRB inhibited treatment and FeRB accelerated treatment, which were lower than 0.025 μg·kg-1. Compared with upland soils, more MeHg was formed in Paddy soils and the concentrations of MeHg in paddy soils were 4-9 times of that in upland soils. Variation in the number of SRB in soils was similar to that in the concentration of MeHg in soils, and the number of SRB was positively correlated with the concentration of MeHg concentrations in soils(R2=0.57,P<0.01). The above results indicated that activities of reducing bacteria, especially SRB, played key role in the methylation in soils. In addition, more attention should be paid to paddy soils due to the high potential of methylation when conducting any assessment and taking any measure to manage the health risk caused by the exposure to mercury.

Microbiological observations in the anoxic basin Golfo Dulce, Costa Rica.

Our basic microbiological studies of the water column and the sediment of Golfo Dulce, Costa Rica, were focused on aerobic and denitrifying sulfur-oxidizing bacteria and anaerobic sulfate-reducing bacteria. We observed no increasing numbers of total bacterial counts within the water column. Although no oxygen was present hydrogen sulfide was only detectable close to the sediment. The highest numbers of sulfate-reducing bacteria measured by Most-Probable-Number counts were found in or close to the sediment. In the anoxic bottom water sulfide-oxidizing bacteria typically containing large sulfur globules were observed microscopically. They were identified as free-swimming Thiovulum and Thiospira species. At one station large vacuolated forms of the filamentous colourless sulfur bacterium Beggiatoa were noted. Together with these sulfur containing bacteria there were long free swimming rods showing no sulfur inclusions of unknown character. The microscopic observations showed good correlation with Most-Probable-Number-counts and molecular biological techniques for sulfate-reducing bacteria.