Sulfate-reducing Bacteria Community Research Articles

Aragonite crystallization in a sulfate-rich hypersaline wetland under dry Mediterranean climate (Laguna Honda, eastern Guadalquivir basin, S Spain)

This research investigates the influence of water composition, the presence of seasonal algal mats, detrital inputs and the activity of microorganisms on the crystallization of aragonite in the sediments deposited in the hypersaline Laguna Honda wetland (S of Spain). The high alkaline and hypersaline waters (pH > 9.2 and C.E. > 70 mS/cm) of the wetland lake are rich in SO42− (>24,000 mg/l), Cl− (>21,000 mg/l), Na+ (>11,000 mg/l) Mg2+ (>8400 mg/l) and Ca2+ (>1000 mg/l), and are supersaturated for dolomite, calcite and aragonite. Sediments have lower pH values than column waters, oscillating from 8.54 in the low Eh (up to −80.9 mV) central deep sediments and 6.33 in the shallower higher Eh (around −13.6 mV) shore sediments. Erosion of the surrounding olive groves soils produced detrital silicates rich sediments with concretions of carbonate or sulfate. Aragonite (up to 19 %) and pyrite (up to 13 %) are mainly concentrated in the organic matter rich samples from the upper part of the sediment cores, whereas gypsum is preferably concentrated in low organic matter content samples. Mineral crusts containing a MgAl silicate phase, epsomite, halite and gypsum are precipitated on the floating algal mats covering the wetland waters. Floating algal mats deposit increased the organic matter content of the upper sediments which promoted the presence of fermentative microorganisms, sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) communities and variations of Eh that influence the authigenesis of carbonate and S-bearing minerals. Replacement of poorly crystalline MgSi phases infilling algal cells by aragonite was favored in the organic matter rich sediments with low Eh values and important SRB communities that promoted sulfate bioreduction processes to form pyrite. Aragonite precipitation was favored by the increase of carbonate and bicarbonate concentration produced by the SRB oxidation of organic matter, the CO2 degassing by high summer temperatures and the CO2 uptake by photosynthesis of the algal mats.

Sulfate reduction behavior in response to landfill dynamic pressure changes

During the long-term stabilization process of landfills, the pressure field undergoes constant changes. This study constructed dynamic pressure changes scenarios of high-pressure differentials (0.6 MPa) and low-pressure differentials (0.2 MPa) in the landfill pressure field at 25 °C and 50 °C, and investigated the sulfate reduction behavior in response to landfill dynamic pressure changes. The results showed that the pressurization or depressurization of high-pressure differentials caused more significant differences in sulfate reduction behavior than that of low-pressure differentials. The lowest hydrogen sulfide (H2S) release peak concentration under pressurization was only 29.67% of that under initial pressure condition; under depressurization, the highest peak concentration of H2S was up to 21,828 mg m−3, posing a serious risk of H2S pollution. Microbial community and correlation analysis showed that pressure had a negative impact on the sulfate-reducing bacteria (SRB) community, and the SRB community adjusted its structure to adapt to pressure changes. Specific SRBs were further enriched with pressure changes. Differential H2S release behavior under pressure changes in the 25 °C pressure environments were mediated by Desulfofarcimen (ASV343) and Desulfosporosinus (ASV1336), while Candidatus Desulforudis (ASV24) and Desulfohalotomaculum (ASV94) played a key role at 50 °C. This study is helpful in the formulation of control strategies for the source of odor pollution in landfills.

Biomineralization To Prevent Microbially Induced Corrosion on Concrete for Sustainable Marine Infrastructure.

Microbially induced corrosion (MIC) on concrete represents a serious issue impairing the lifespan of coastal/marine infrastructure. However, currently developed concrete corrosion protection strategies have limitations in wide applications. Here, a biomineralization method was proposed to form a biomineralized film on concrete surfaces for corrosion inhibition. Laboratory seawater corrosion experiments were conducted under different conditions [e.g., chemical corrosion (CC), MIC, and biomineralization for corrosion inhibition]. A combination of chemical and mechanical property measurements of concrete (e.g., sulfate concentrations, permeability, mass, and strength) and a genotypic-based investigation of formed concrete biofilms was conducted to evaluate the effectiveness of the biomineralization approach on corrosion inhibition. The results show that MIC resulted in much higher corrosion rates than CC. However, the biomineralization treatment effectively inhibited corrosion because the biomineralized film decreased the total and relative abundance of sulfate-reducing bacteria (SRB) and acted as a protective layer to control the diffusion of sulfate and isolate the concrete from the corrosive SRB communities, which helps extend the lifespan of concrete structures. Moreover, this technique had no negative impact on the native marine microbial communities. Our study contributes to the potential application of biomineralization for corrosion inhibition to achieve long-term sustainability for major marine concrete structures.

Community ecological study on the reduction of soil antimony bioavailability by SRB-based remediation technologies

Sulfate-reducing bacteria (SRB) were effective in stabilizing Sb. However, the influence of electron donors and acceptors during SRB remediation, as well as the ecological principles involved, remained unclear. In this study, Desulfovibrio desulfuricans ATCC 7757 was utilized to stabilize soil Sb within microcosm. Humic acid (HA) or sodium sulfate (Na2SO4) were employed to enhance SRB capacity. The SRB+HA treatment exhibited the highest Sb stabilization rate, achieving 58.40%. Bacterial community analysis revealed that SRB altered soil bacterial diversity, community composition, and assembly processes, with homogeneous selection as the predominant assembly processes. When HA and Na2SO4 significantly modified the stimulated microbial community succession trajectories, shaped the taxonomic composition and interactions of the bacterial community, they showed converse effect in shaping bacterial community which were both helpful for promoting dissimilatory sulfate reduction. Na2SO4 facilitated SRB-mediated anaerobic reduction and promoted interactions between SRB and bacteria involved in nitrogen and sulfur cycling. The HA stimulated electron generation and storage, and enhanced the interactions between SRB and bacteria possessing heavy metal tolerance or carbohydrate degradation capabilities.

Impacts of phosphorus and nitrogen absence on microbial diversity and sulfate removal in anaerobic batch reactors

Sulfate-rich effluents have been successfully treated in anaerobic reactors using sulfate-reducing bacteria (SRB). Many authors have demonstrated that these systems require nitrogen and phosphorous supplementation to achieve high sulfate removal rates. However, the resource ratio theory assumes that some species can be dominant according to the nutritional relations used or even without external nutrient supplementation. Thus, this study evaluated the SRB communities in batch reactors without external nitrogen and phosphorus sources based on most probable number (MPN) quantification, denaturing gradient gel electrophoresis (DGGE) analyses and sequencing. The sulfate and chemical oxygen demand (COD) removal and kinetic parameters were also determined. After 100 days of operation, the sulfate and COD removal achieved 71.8 ± 10% and 86.5 ± 10%, respectively. The SRB population increased from 8.106 to 4 × 1012 MPN 100 mL−1, and the richness of SRB bands was much higher at the end of the experiment compared to the inoculum. In addition, the sequenced bands from SRB-DGGE showed similarities to Desulfacinum infernum, Desulfobulbus sp, Syntrophobacter and Desulfomicrobium aestuarii-related sequences. Therefore, biological treatment of acid mine drainage wastewater was effective in the absence of nutrients, lowering costs and providing high sulfate removal efficiency.

Variation of sulfate reducing bacteria communities in ionic rare earth tailings and the potential of a single cadmium resistant strain in bioremediation

Heap leaching ionic rare earth tailings might be prone to nourish sulfate reducing bacteria (SRB), but the SRB community in terrestrial ecosystems, such as tailings, has never been studied. This work was conducted to investigate the SRB communities in revegetated and bare tailings in Dingnan county, Jiangxi province, China, incorporating with indoor experiments to isolate SRB strain in bioremediation of Cd contamination. Significant increases in richness, accompanied by reductions in evenness and diversity, were found in the SRB community in revegetated tailings compared to bare tailings. At genus taxonomic level, two distinct dominant SRB were observed in samples from bare and revegetated tailings, with Desulfovibrio dominating in the former and Streptomyces dominating in the latter, respectively. A single SRB strain was screened out from the bare tailings (REO-01). The cell of REO-01 was rod-shaped and belonged to family Desulfuricans and genus Desulfovibrio. The Cd resistance of the strain was further examined, no changes in cell morphology were observed at 0.05 mM Cd, additionally, the atomic ratios of S, Cd, and Fe changed with the increase in Cd dosages, indicating FeS and CdS were produced simultaneously, XRD results further confirmed the production changed gradually from FeS to CdS with increasing Cd dosages from 0.05 to 0.2 mM. FT-IR analysis showed that functional groups containing amide, polysaccharide glycosidic linkage, hydroxyl, carboxy, methyl, phosphodiesters and sulfhydryl groups in extracellular polymeric substances (EPS) of REO-01 might have affinity with Cd. This study demonstrated the potential of a single SRB strain isolated from ionic rare earth tailings in bioremediation of Cd contamination.

Active Sulfate-Reducing Bacterial Community in the Camel Gut

The diversity and activity of sulfate-reducing bacteria (SRB) in the camel gut remains largely unexplored. An abundant SRB community has been previously revealed in the feces of Bactrian camels (Camelus bactrianus). This study aims to combine the 16S rRNA gene profiling, sulfate reduction rate (SRR) measurement with a radioactive tracer, and targeted cultivation to shed light on SRB activity in the camel gut. Fresh feces of 55 domestic Bactrian camels grazing freely on semi-arid mountain pastures in the Kosh-Agach district of the Russian Altai area were analyzed. Feces were sampled in early winter at an ambient temperature of -15 °C, which prevented possible contamination. SRR values measured with a radioactive tracer in feces were relatively high and ranged from 0.018 to 0.168 nmol S cm-3 day-1. The 16S rRNA gene profiles revealed the presence of Gram-negative Desulfovibrionaceae and spore-forming Desulfotomaculaceae. Targeted isolation allowed us to obtain four pure culture isolates belonging to Desulfovibrio and Desulforamulus. An active SRB community may affect the iron and copper availability in the camel intestine due to metal ions precipitation in the form of sparingly soluble sulfides. The copper-iron sulfide, chalcopyrite (CuFeS2), was detected by X-ray diffraction in 36 out of 55 analyzed camel feces. In semi-arid areas, gypsum, like other evaporite sulfates, can be used as a solid-phase electron acceptor for sulfate reduction in the camel gastrointestinal tract.

Recovery of copper-dominated resources from copper mine drainage by chemical oxidation and sulfur biocycling: A pilot-scale study

The copper mine drainage (CMD) formed during copper mining and smelting has the characteristics of being low pH, with a high sulfate concentration and large amounts of metal ions such as Fe, Cu, and Mn. In order to recover copper-dominated many resources from CMD, realize effective control of environmental pollution and avoid the loss of precious resources. The combined process of Fe pretreatment recovery, Cu treatment recovery, and S treatment recovery was established based on H2O2 oxidation, sulfate-reducing bacteria (SRB) reduction, and sulfur-oxidizing bacteria oxidation. A pilot-scale study was carried out with a CMD inlet flow rate of 12 m³/d. Results show that the average Cu2+ removal rate was 99.66%, and the recovered dry matter precipitated (mainly was CuS) copper content was 35.6%. In addition, the average total Fe, Mn and Mg removal rate was 99.46%, 99.10% and 84.08%. And the S2− oxidation rate was above 90% (mainly converted to sulfur). 27.52% Fe precipitated dry matter and 42.9% S, 32.2% Mg, and 13.8% Mn precipitated dry matter were also recovered as by-products. Through high-throughput analysis of the functional and structural changes in the SRB community, showed that indigenous SRB from the copper mine exhibit good adaptability to CMD conditions, with the enrichment and acclimation of SRBs achieving a high level of expression of bioactive. The bottleneck of SRB applied to CMD treatment was solved. Finally, the economic feasibility analysis shows that the combined process treatment CMD can save 58.6% of the cost compared with traditional lime neutralization method, and avoid the sludge treatment cost of 29.03 million USD per year. The above provides engineering practical reference for CMD treatment and resource recovery.

Enhancement effects of decabromodiphenyl ether on microbial sulfate reduction in eutrophic lake sediments: A study on sulfate-reducing bacteria using dsrA and dsrB amplicon sequencing

Although sulfate (SO42−) reduction by sulfate-reducing bacteria (SRB) is an important sulfur cycling processes, little is known about how the persistent organic pollutants affect the SO42− reduction process in the eutrophic lake sediments. Here, we carried out a 120-day microcosm experiment to explore the effects of decabromodiphenyl ether (BDE-209) on SO42− reduction mediated by SRB in sediment collected from Taihu Lake, a typical eutrophic lake in China. The results showed that BDE-209 contamination significantly enhanced the activity of dissimilatory sulfite reductase (DSR) (r = 0.83), which led to an increased concentration of sulfide produced by SO42− reduction. This stimulatory effect of BDE-209 on DSR activity was closely related to variations in the dsrA- and dsrB-type SRB communities. The abundances and diversities of the dsrA- and dsrB-containing SRB increased and their community composition varied in response to BDE-209 contamination. The gene copies (r = 0.72), Chao 1 (r = 0.50), Shannon (r = 0.55), and Simpson (r = 0.70) indices of dsrB-containing SRB was positively correlated with BDE-209 contamination. Co-occurrence network analysis revealed that network complexity, connectivity, and the interspecific cooperative relationship in SRB were strengthened by BDE-209 contamination. The keystone species identified in the SRB community mainly belonged to the genera Candidatus Sulfopaludibacter for the dsrA-containing SRB and Desulfatiglans for the dsrB-containing SRB, and their relative abundances were positively correlated with DSR activity in the sediment. The relative abundance of the keystone species and SRB diversity were important microbial factors directly contributing to the variations in DSR activity based on structural equation modeling analysis. Notably, the results of abundance, community structure, and interspecific relationships showed that the dsrB-containing SRB may be more sensitive to the BDE-209 contamination than the dsrA-containing SRB. These results will help us understand the effects of BDE-209 on microbial sulfate reduction in eutrophic lakes.

Composition and key-influencing factors of bacterial communities active in sulfur cycling of soda lake sediments.

Bacteria are important participants in sulfur cycle of the extremely haloalkaline environment, e.g. soda lake. The effects of physicochemical factors on the composition of sulfide-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) in soda lake have remained elusive. Here, we surveyed the community structure of total bacteria, SOB and SRB based on 16S rRNA, soxB and dsrB gene sequencing, respectively, in five soda lakes with different physicochemical factors. The results showed that the dominant bacteria belonged to the phyla Proteobacteria, Bacteroidetes, Halanaerobiaeota, Firmicutes and Actinobacteria. SOB and SRB were widely distributed in lakes with different physicochemical characteristics, and the community composition were different. In general, salinity and inorganic nitrogen sources (NH4+-N, NO3--N) were the most significant factors. Specifically, the communities of SOB, mainly including Thioalkalivibrio, Burkholderia, Paracoccus, Bradyrhizobium, and Hydrogenophaga genera, were remarkably influenced by the levels of NH4+-N and salinity. Yet, for SRB communities, including Desulfurivibrio, Candidatus Electrothrix, Desulfonatronospira, Desulfonatronum, Desulfonatronovibrio, Desulfonatronobacter and so on, the most significant determinants were salinity and NO3--N. Besides, Rhodoplanes played a significant role in the interaction between SOB and SRB. From our results, the knowledge regarding the community structures of SOB and SRB in extremely haloalkaline environment was extended.

Carbon‑sulfur coupling in a seasonally hypoxic, high-sulfate reservoir in SW China: Evidence from stable C[sbnd]S isotopes and sulfate-reducing bacteria

Anthropogenic input of sulfate (SO42−) in reservoirs may enhance bacterial sulfate reduction (BSR) under seasonally hypoxic conditions in the water column. However, factors that control BSR and its coupling to organic carbon (OC) mineralization in seasonally hypoxic reservoirs remain unclear. The present study elucidates the coupling processes by analyzing the concentrations and isotopic composition of dissolved inorganic carbon (DIC) and sulfur (SO42−, sulfide) species, and the microbial community in water of the Aha reservoir, SW China, which has high SO42− concentration due to the inputs from acid mine drainage about twenty years ago. The water column at two sites in July and October revealed significant thermal stratification. In the hypoxic bottom water, the δ13C-DIC decreased while the δ34S-SO42− increased, implying organic carbon mineralization due to BSR. The magnitude of S isotope fractionation (Δ34S, obtained from δ34Ssulfate-δ34Ssulfide) during the process of BSR fell in the range of 3.4‰ to 27.0‰ in July and 21.6‰ to 31.8‰ in October, suggesting a change in the community of sulfate-reducing bacteria (SRB). The relatively low water column stability in October compared to that in July weakened the difference of water chemistry and ultimately affected the SRB diversity. The production of DIC (ΔDIC) scaled a strong positive relationship with the Δ34S in July (p < 0.01), indicating that high OC availability favored the survival of incomplete oxidizers of SRB. However, in October, Δ13C-DIC was correlated with the Δ34S in the bottom hypoxic water (p < 0.01), implying that newly degraded OC depleted in 13C could favor the dominance of complete oxidizers of SRB which caused greater S isotope fractionation. Moreover, the sulfide supplied by BSR might stimulate the reductive dissolution of Fe and Mn oxides (Fe(O)OH and MnO2). The present study helps to understand the coupling of C and S in seasonally hypoxic reservoirs characterized by high SO42− concentration.

Black blooms-induced adaptive responses of sulfate reduction bacteria in a shallow freshwater lake

Decomposing cyanobacterial bloom-induced black blooms been seen as an issue in the management of freshwater ecosystems, but its effect on sulfate-reducing bacteria (SRB) in shallow freshwater lakes is not clear. The objective of this study is to present an in-depth investigation of black bloom effects on the activities and composition of SRB, as well as the interactions between SRB and other bacteria. Water and surface sediments samples were collected from a shallow freshwater lake during black and non-black blooms. Sulfate reduction rates (SRRs) in the water column were determined from the linear regression of sulfate depletion with time. Quantitative real-time polymerase chain reactions (qPCRs), targeting the dsrA gene and Illumina sequencing of 16S rDNA, were used to estimate the SRB population and SRB community structures, respectively. Our data indicate that although a higher abundance of SRB was responsible for the higher SRR in the bottom water (34.09 ± 2.37 nmol mL−1 day−1) than in the surface water (14.57 ± 2.91 nmol mL−1 day−1) during black blooms, cell-specific sulfate reduction rates (csSRRs) in the distinct water layers were not significantly different (P = 0.95), with the value of approximately 0.017 fmol cell−1 day−1. Additionally, Desulfomicrobium and Desulfovibrio were the two main genera of SRB in the water column during black bloom season, while Desulfobulbus, Desulfobacca and Desulfatiglans genera were identified in the sediments of both the black and non-black blooms in genera pools. Each SRB genus preferentially associated with bacteria for specific functions in the bacterial co-occurrence network, regardless of whether black booms occurred or not. These results extend our knowledge on the importance of SRB during black blooms and the adaptation of SRB to environmental changes in freshwater lakes.

Pengaruh Nitrat terhadap Biokorosi Logam oleh Konsorsium Bakteri Pereduksi Sulfat dari PLTA Saguling

&lt;div&gt;&lt;strong&gt;The Influence of Nitrate in Metal Biocorrosion caused by Sulfate Reducing Bacteria from Saguling Hydropower&lt;/strong&gt;. The corrosion facilitated and accelerated by the activities of microorganism is called biocorrosion. Sulfate reducing bacteria (SRB) is known as the bacteria that cause biocorrosion in anaerobic condition by using sulfate as the final electron acceptor. Biocorrosion reduces equipment lifetime and increases maintenance cost in industry. In the cooling system in Saguling hydropower, corrosion was commonly caused by utilization of contaminated water due to anorganic and organic waste, especially sulfate. In this research, sulfate reducing bacteria was isolated from biofilms in the cooling system of Saguling Hydropower. Molecular analysis using PCR-DGGE method with dsrB gene (350 bp) as molecular markers showed that SRB consortium contained 12 bands and assumed as different species of SRB. SRB consortium was tested to determine its biocorrosion activity over metal material of ST37 (carbon steel) and SUS304 (stainless steel). The consortium then treated with 7 different nitrate concentrations to determine its effect against the sulfate reducing bacteria activity. SRB consortium caused higher corrosion to ST37 than SUS304L, with the corrosion rate of 0.07660 mm/year and 0.00265 mm/year, respectively. Concentration of 10 mM nitrate effectively inhibited corrosion rate on ST37 and caused the changes in sulfate reducing bacteria communities, indicated by the disappearance of 6 bands in DGGE profile&lt;/div&gt;

Optimal start-up conditions for the efficient treatment of acid mine drainage using sulfate-reducing bioreactors based on physicochemical and microbiome analyses

Typically, sulfate-reducing bioreactors used to treat acid mine drainage (AMD) undergo an initial incubation period of a few weeks to acclimatize sulfate-reducing bacteria (SRB), although necessity of this preincubation has rarely been evaluated. To reduce time and economic cost, we developed an SRB acclimatization method using the continuous flow of AMD into bioreactors fed with rice bran, and compared with the conventional acclimatization method. We found that the SRB sufficiently acclimatized without the preincubation phase. Furthermore, we examined the performance and SRB communities in bioreactors operated for >200 days under seven different conditions, in which the amount of rice bran added and hydraulic retention times (HRTs) were varied. A comparison of the various bioreactor conditions revealed that the lowest rice bran amount (50 g) and the shortest HRT (6 h) caused a deterioration in reactor performance after day 144 and 229, respectively. In both cases, relatively aerobic environments developed due to the lack of organic matter seemed to inhibit sulfate reduction. Of the conditions tested, operation of the bioreactors with 200 g of rice bran and an HRT of 12.5 h was the most effective in treating AMD, showing a sulfate reduction rate of 20.7–77.9% during days 54–242. Data and materials availabilityAll data needed to evaluate the conclusions of this study are presented in the paper and/or the appendix.

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

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

Human activities can drive sulfate-reducing bacteria community in Chinese intertidal sediments by affecting metal distribution

Sulfate-reducing bacteria (SRB), which are ubiquitous in intertidal sediments, play an important role in global sulfur and carbon cycles, and in the bioremediation of toxic metalloids/metals. Pollution from human activities is now a major challenge to the sustainable development of the intertidal zone, but little is known about how and to what extent various anthropic and/or natural factors affect the SRB community. In the current study, based on the dsrB gene, we investigated the SRB community in intertidal sediment along China's coastline. The results showed that dsrB gene abundances varied among different sampling sites, with the highest average abundance of SRB at XHR (near the Bohai Sea). The SRB community structures showed obvious spatial distribution patterns with latitude along the coastal areas of China, with Desulfobulbus generally being the dominant genus. Correlation analysis and redundancy discriminant analysis revealed that total organic carbon (TOC) and pH were significantly correlated with the richness of the SRB community, and salinity, pH, sulfate and climatic parameters could be the important natural factors influencing the composition of the SRB community. Moreover, metals, especially bioavailable metals, could regulate the diversity and composition of the SRB communities. Importantly, according to structural equation model (SEM) analysis, anthropic factors (e.g., population, economy and industrial activities) could drive SRB community diversity directly or by significantly affecting the concentrations of metals. This study provides the first comprehensive investigation of the direct and indirect anthropic factors on the SRB community in intertidal sediments on a continental scale.

Effect of PAHs on nitrogen-fixing and sulfate-reducing microbial communities in seagrass Enhalus acoroides sediment.

Seagrass meadows are vital ecosystems with high productivity and biodiversity and often in the oligotrophic area. Nitrogen usually limits productivity in this ecosystem as the main nutrient factor. Biological nitrogen fixation by diazotrophs in the rhizosphere sediment can introduce "new" nitrogen into the ecosystem. Previous studies revealed that most sulfate-reducing bacteria (SRB) can also fix nitrogen like the nitrogen-fixing bacteria (NFB). Moreover, both sulfate reduction and nitrogen fixation were affected by the organic pollutant. However, rare information is available regarding the NFB and SRB community composition and their temporal response to the pollutant. The quantitative real-time polymerase chain reaction and polymerase chain reaction denaturing gradient gel electrophoresis have been used to analyze NFB and SRB communities' shifts under different PAHs concentrations. They both experienced a dramatic shift under PAHs stress but exhibited different patterns. SRB could use the low and high concentration PAHs at the early stage of the incubation, while only the low concentration of PAHs could stimulate the growth of NFB through the whole incubation period. The predominant species of NFB communities were Alphaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria; while for SRB communities were class Epsilonproteobacteria. Redundancy analysis indicated the significant environmental factors for the two communities were both ammonium and pH (P < 0.05). There existed nifH sequences related to known nitrogen fixing SRB Desulfatibacillum alkenivorans, which confirmed that microbial N2 fixation and sulfate reduction were coupled in the seagrass ecosystem by molecular technique. Our investigation provides new insight into the NFB and SRB community in the seagrass meadow.

Sulfate-reducing bacterial community shifts in response to acid mine drainage in the sediment of the Hengshi watershed, South China.

Sulfate-reducing bacteria (SRB) are an attractive option for treating acid mine drainage (AMD) and are considered to be of great significance in the natural attenuation of AMD, but the available information regarding the highly diverse SRB community in AMD sites is not comprehensive. The Hengshi River, which is continually contaminated by AMD from upstream mining areas, was selected as a study site for investigation of the distribution, diversity, and abundance of SRB. Overall, high-throughput sequencing of the 16S rRNA and dsrB genes revealed the high diversity, richness, and OTU numbers of SRB communities, suggesting the existence of active sulfate reduction in the study area. Further analysis demonstrated that AMD contamination decreased the richness and diversity of the microbial community and SRB community, and led to spatiotemporal shifts in the overall composition and structure of sediment microbial and SRB communities along the Hengshi watershed. However, the sulfate reduction activity was high in the midstream, even though AMD pollution remained heavy in this area. Spatial distributions of SRB community indicated that species of Clostridia may be more tolerant of AMD contamination than other species, because of their predominance in the SRB communities. In addition, the results of CCA revealed that environmental parameters, such as pH, TS content, and Fe content, can significantly influence total microbial and SRB community structure, and dissolved organic carbon was another important factor structuring the SRB community. This study extends our knowledge of the distribution of indigenous SRB communities and their potential roles in natural AMD attenuation.

Identification of sulfate-reducing and methanogenic microbial taxa in anaerobic bioreactors from industrial wastewater treatment plants using next-generation sequencing and gene clone library analyses

An understanding of microbial communities present in anaerobic bioreactors can strongly facilitate the development of approaches to control undesirable microorganisms, such as sulfate-reducing bacteria (SRB), in the system. In this study, overall microbial communities present in anaerobic bioreactors from seven industrial wastewater treatment plants (including food, pulp and paper industries) were investigated using 16S rRNA gene amplicon sequencing (MiSeq, Illumina). The dominant methanogens identified in the anaerobic bioreactors treating industrial wastewater were Methanobacterium and Methanosaeta; Methanospirillum was a predominant methanogen in the anaerobic sludge digester. Hydrogenotrophic and acetoclastic methanogens were detected at similar relative abundances in the anaerobic covered lagoons treating starch wastewater, whereas hydrogenotrophic methanogens were the predominant methanogens present in the sludge digester. SRB communities were further investigated using dsrB gene clone libraries. The results indicated the presence of SRB, such as uncultured Desulfobulbus sp., Syntrophobacter fumaroxidans, Syntrophorhabdus sp. PtaB.Bin027, and Desulfovibrio fructosivarans JJ. Incomplete-oxidizing SRB were the predominant SRB in all of the anaerobic bioreactors treating wastewater. In contrast, similar relative abundances of complete and incomplete-oxidizing SRB were observed in the sludge digester. The results of this study can further facilitate the development of SRB-controlling strategies to improve the efficiency of wastewater treatment.

Growth inhibition of sulfate-reducing bacteria for trichloroethylene dechlorination enhancement

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