Species Of Sulfate-reducing Bacteria Research Articles

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

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

Abundance, geo-microbial role and community diversity of sulfate-reducing bacteria in tropical estuarine sediments

Sulfate-reducing bacteria (SRB), a diverse taxonomic group of anaerobic microorganisms that oxidize sulfur compounds as terminal electron acceptors, drive the key biogeochemical process of sulfate reduction. However, little is known about the diversity of SRB in tropical coastal habitats. Thus, the goal of this study is to explore and compare the community diversity of the Ashtamudi and Vembanad estuaries and evaluate the sedimentary sulfate reduction rate. The microbiome profiling of SRB was carried out using Next Generation Sequencing (NGS) techniques (Illumina sequencing) based on gene amplification of the dissimilatory sulfate reductase (dsr) enzyme to confirm the diversity and dominant taxa of SRB. The diversity of SRB represented by the Shannon alpha diversity index of the Ashtamudi estuary (6.55) was two-fold that of the Vembanad estuary. In the Vembanad estuary, the marine zone (4.09) harboured more diversity than the freshwater zone (1.825). Higher diversity and lower abundant taxa in the Ashtamudi estuary pointed out the presence of a rare biosphere that has not yet been studied. It was interesting to note that both estuaries have the same SRB phylum diversity. At the level of species, however, there was a noticeable difference. This differential diversity of SRB has an apparent influence on methane production during the breakdown of organic matter in addition to sulfate reduction. Several species of SRB have an important role in the biodegradation of persistent pollutants and the removal of heavy metals.

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

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

Molecular regulation of conditioning film formation and quorum quenching in sulfate reducing bacteria.

Sensing surface topography, an upsurge of signaling biomolecules, and upholding cellular homeostasis are the rate-limiting spatio-temporal events in microbial attachment and biofilm formation. Initially, a set of highly specialized proteins, viz. conditioning protein, directs the irreversible attachment of the microbes. Later signaling molecules, viz. autoinducer, take over the cellular communication phenomenon, resulting in a mature microbial biofilm. The mandatory release of conditioning proteins and autoinducers corroborated the existence of two independent mechanisms operating sequentially for biofilm development. However, both these mechanisms are significantly affected by the availability of the cofactor, e.g., Copper (Cu). Generally, the Cu concentration beyond threshold levels is detrimental to the anaerobes except for a few species of sulfate-reducing bacteria (SRB). Remarkably SRB has developed intricate ways to resist and thrive in the presence of Cu by activating numerous genes responsible for modifying the presence of more toxic Cu(I) to Cu(II) within the periplasm, followed by their export through the outer membrane. Therefore, the determinants of Cu toxicity, sequestration, and transportation are reconnoitered for their contribution towards microbial adaptations and biofilm formation. The mechanistic details revealing Cu as a quorum quencher (QQ) are provided in addition to the three pathways involved in the dissolution of cellular communications. This review articulates the Machine Learning based data curing and data processing for designing novel anti-biofilm peptides and for an in-depth understanding of QQ mechanisms. A pioneering data set has been mined and presented on the functional properties of the QQ homolog in Oleidesulfovibrio alaskensis G20 and residues regulating the multicopper oxidase properties in SRB.

The selectivity of electron acceptors for the removal of caffeine, gliclazide, and prazosin in an up-flow anaerobic sludge blanket (UASB) reactor.

This study attempts to investigate the relationship between the dominance of reducing conditions and the biotransformation of pharmaceutical compounds, which has been scarcely reported in a continuous anaerobic treatment process. Previous batch experiments have discovered the possible implications of different reducing conditions on the biotransformation process, but have failed to reflect actual removal performance due to substrate limitations and other operational factors. Continuously operating reactors commonly receive wastewater stream containing a wide range of electron acceptors that diversify the growth of microorganisms in anaerobic treatment. The alteration of the dominance of reducing conditions in a continuous anaerobic reactor may result in the improvement of biotransformation performance compared to a single reducing condition in a substrate-limited batch experiment. The removal of psychostimulant caffeine (CAF), anti-diabetic drug gliclazide (GCZ), and anti-hypertensive drug prazosin (PRZ) were examined through the operation of an up-flow anaerobic sludge blanket (UASB) reactor under predominant methanogenic condition (Phase I) and simultaneous reducing conditions provided by a nitrate supplement (Phase II). The results revealed high biotransformation performance for all three compounds (73-> 99%) in both Phase I and Phase II experiments and fitted the pseudo-first-order model. The biotransformation rate of CAF and PRZ were relatively lower by 25% and 29%, while the GCZ rate improvement doubled in Phase II compared to Phase I. The outcome from 16s rRNA sequencing suggested that the biotransformation of the compounds may be driven by Firmicutes and Bacteroidota in both phases, and Burkhorderiales and sulfate-reducing bacteria species in Phase II. This study proved preferential of reducing conditions does not negatively affect the biotransformation performance of each pharmaceutical compound in a continuous anaerobic reactor, but they led to varying biotransformation rate, hence shifting the microbial diversity.

Acetate Degradation at Low pH by the Moderately Acidophilic Sulfate Reducer Acididesulfobacillus acetoxydans gen. nov. sp. nov.

In acid drainage environments, biosulfidogenesis by sulfate-reducing bacteria (SRB) attenuates the extreme conditions by enabling the precipitation of metals as their sulfides, and the neutralization of acidity through proton consumption. So far, only a handful of moderately acidophilic SRB species have been described, most of which are merely acidotolerant. Here, a novel species within a novel genus of moderately acidophilic SRB is described, Acididesulfobacillus acetoxydans gen. nov. sp. nov. strain INE, able to grow at pH 3.8. Bioreactor studies with strain INE at optimum (5.0) and low (3.9) pH for growth showed that strain INE alkalinized its environment, and that this was more pronounced at lower pH. These studies also showed the capacity of strain INE to completely oxidize organic acids to CO2, which is uncommon among acidophilic SRB. Since organic acids are mainly in their protonated form at low pH, which increases their toxicity, their complete oxidation may be an acid stress resistance mechanism. Comparative proteogenomic and membrane lipid analysis further indicated that the presence of saturated ether-bound lipids in the membrane, and their relative increase at lower pH, was a protection mechanism against acid stress. Interestingly, other canonical acid stress resistance mechanisms, such as a Donnan potential and increased active charge transport, did not appear to be active.

Removal of Antimony in Wastewater by Antimony Tolerant Sulfate-Reducing Bacteria Isolated from Municipal Sludge.

Antimony (Sb), a global and priority controlled pollutant, causes severe environmental issues. Bioremediation by microbial communities containing sulfate-reducing bacteria (SRB) is considered to be among the safest, economical, and environmentally friendly methods to remove Sb from wastewater. However, the roles of SRB species in these communities remain uncertain, and pure cultures of bacteria that may be highly efficient have not yet been developed for Sb removal. In this study, an Sb tolerant community was enriched from municipal sludge, and molecular ecological analysis showed that Escherichia (40%) and Desulfovibrio (15%) were the dominant bacteria. Further isolation and identification showed that the enriched SRB strains were closely related to Cupidesulfovibrio oxamicus, based on the molecular analyses of 16S rRNA and dsrB genes. Among them, a strain named SRB49 exhibited the highest activity in removal of Sb(V). SRB49 was able to remove 95% of Sb(V) at a concentration of 100 mg/L within 48 h under optimum conditions: a temperature of 37–40 °C, an initial pH value of 8, 4 mM of sulfate, and an initial redox potential of 145–229 mV. SEM-EDX analysis showed that SRB49 did not adsorb Sb(V) but reduced and precipitated Sb(V) via the formation of Sb2S3. The results demonstrated the potential roles that pure cultures of SRB species may play in Sb removal and the use of Sb-tolerant SRB strains for Sb remediation.

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

<div><strong>The Influence of Nitrate in Metal Biocorrosion caused by Sulfate Reducing Bacteria from Saguling Hydropower</strong>. 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</div>

Characterization of the biofilm structure and microbial diversity of sulfate-reducing bacteria from petroleum produced water supplemented by different carbon sources

Colonization by sulfate-reducing bacteria (SRB) in environments associated with oil is mainly dependent on the availability of sulfate and carbon sources. The formation of biofilms by SRB increases the corrosion of pipelines and oil storage tanks, representing great occupational and operational risks and respective economic losses for the oil industry. The aim of this study was to evaluate the influence of the addition of acetate, butyrate, lactate, propionate and oil on the structure of biofilm formed in carbon steel coupons, as well as on the diversity of total bacteria and SRB in the planktonic and sessile communities from petroleum produced water. The biofilm morphology, chemical composition, average roughness and the microbial diversity was analyzed. In all carbon sources, formation of dense biofilm without morphological and/or microbial density differences was detected, with the most of cells observed in the form of individual rods. The diversity and richness indices of bacterial species in the planktonic community was greater than in the biofilm. Geotoga was the most abundant genus, and more than 85% of SRB species were common to all treatments. The functional predicted profile shown that the observed genres in planktonic communities were related to the reduction of sulfate, sulfite, elementary sulfur and other sulfur compounds, but the abundance varied between treatments. For the biofilm, the functions predicted profile for the oil treatment was the one that most varied in relation to the control, while for the planktonic community, the addition of all carbon sources interfered in the predicted functional profile. Thus, although it does not cause changes in the structure and morphology biofilm, the supplementation of produced water with different carbon sources is associated with changes in the SRB taxonomic composition and functional profiles of the biofilm and the planktonic bacterial communities.

Desulfovibrio diazotrophicus sp. nov., a sulfate-reducing bacterium from the human gut capable of nitrogen fixation.

Sulfate-reducing bacteria (SRB) are widespread in human guts, yet their expansion has been linked to colonic diseases. We report the isolation, sequencing and physiological characterization of strain QI0027T , a novel SRB species belonging to the class Desulfovibrionia. Metagenomic sequencing of stool samples from 45 Chinese individuals, and comparison with 1690 Desulfovibrionaceae metagenome-assembled genomes recovered from humans of diverse geographic locations, revealed the presence of QI0027T in 22 further individuals. QI0027T encoded nitrogen fixation genes and based on the acetylene reduction assay, actively fixed nitrogen. Transcriptomics revealed that QI0027T overexpressed 42 genes in nitrogen-limiting conditions compared to cultures supplemented with ammonia, including genes encoding nitrogenases, a urea uptake system and the urease complex. Reanalyses of 835 public stool metatranscriptomes showed that nitrogenase genes from Desulfovibrio bacteria were expressed in six samples suggesting that nitrogen fixation might be active in the gut environment. Although frequently thought of as a nutrient-rich environment, nitrogen fixation can occur in the human gut. Animals are often nitrogen limited and have evolved diverse strategies to capture biologically active nitrogen, ranging from amino acid transporters to stable associations with beneficial microbes that provide fixed nitrogen. QI0027T is the first Desulfovibrio human isolate for which nitrogen fixation has been demonstrated, suggesting that some sulfate-reducing bacteria could also play a role in the availability of nitrogen in the gut.

Gut Microbiome Contributes to the Development of Behcet's Disease Via Adjuvant Effects

BACKGROUND: Behcet’s disease (BD) is associated with considerable gut microbiome changes. However, it still remains unknown how the composition of the gut microbiome exactly affects the development of this disease. METHODS AND FINDINGS: In this study, transplantation of stool samples from patients with active ocular BD to mice via oral gavage was performed. This resulted in decreases of three short chain fatty acids (SCFAs) including butyric acid, propionic acid and valeric acid in association with enrichment of several species of sulfate-reducing bacteria (SRB) and a reduction of butyrate-producing bacteria (BPB). Intestinal barrier integrity of mice receiving BD feces was damaged as shown by a decreased expression of tight junction proteins and was associated with the release of Lipopolysaccharides (LPS) in the circulation. The mice also showed a higher frequency of splenic neutrophils as well as an enrichment of genes associated with innate immune responses in the neutrophils and CD4+T cells as identified by single cell RNA sequencing. Analysis of neutrophils and T cells functions in these mice showed an enhanced mesenteric lymph node and splenic Th1 and Th17 cell differentiation as well as down-regulation of Tregs in association with activation of neutrophils. Transplantation of BD feces to mice and subsequent induction of experimental uveitis (EAU) or encephalomyelitis (EAE) led to an exacerbation of disease in both models, suggesting a microbial adjuvant effect. INTERPRETATION: These findings suggest that the gut microbiome can regulate an autoimmune response via adjuvant effects including increased gut permeability and enhancement of innate immunity. FUNDING: This study was supported by National Natural Science Foundation Key Program (81930023), Natural Science Foundation Major International (Regional) Joint Research Project (81720108009), Chongqing Outstanding Scientists Project (2019) , Chongqing Key Laboratory of Ophthalmology (CSTC, 2008CA5003), Chongqing Science & Technology Platform and Base Construction Program (cstc2014pt-sy10002) and the Chongqing Chief Medical Scientist Project (2018). Declaration of Interest: The authors declare that they have no conflict of interest. Ethical Approval: The study was approved by the Ethics Committee of Chongqing Medical University. Signed informed consent was obtained from all participants at the beginning of the study. All procedures were performed in accordance with the Declaration of Helsinki.

Microbial community compositions and sulfate-reducing bacterial profiles in malodorous urban canal sediments.

Anthropogenically impacted urban canals represent distinct freshwater ecosystems that could shape microbial communities in underlying sediments; however, knowledge of the relationships between environmental factors and microbial community compositions and their functions in such an environment is limited. This study characterized the microbial community compositions of malodorous canal sediments at six locations along the Saen Saep Canal in Thailand. 16S rRNA gene amplicon sequencing (MiSeq, Illumina) revealed dominant genera classified as fermentative bacteria, methanogens, and sulfate-reducing bacteria (SRB), all of which emphasized anaerobic environments. SRB, as the primary producers of malodorous hydrogen sulfide, accounted for 8.2-30.4% of the total sequences. dsrB gene clone libraries further identified the SRB species. A constrained correspondence analysis demonstrated a spatial pattern of SRB that correlated with physicochemical parameters in which nitrate and sulfate in sediments were the most influencing factors. Overall, a better understanding of the SRB and other related microorganisms in canal sediments can assist in the future implementation of appropriate olfactory abatement and management methodologies in urban canals.

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

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

Effect of pH regulation by sulfate-reducing bacteria on corrosion behaviour of duplex stainless steel 2205 in acidic artificial seawater.

Sulfate-reducing bacteria (SRB) can regulate environmental pH because of their metabolism. Because local acidification results in pitting corrosion, the potential capacity of pH regulation by SRB would have important consequences for electrochemical aspects of the bio-corrosion process. This study focused on identifying the effect of pH on the corrosion of duplex stainless steel 2205 in a nutrient-rich artificial seawater medium containing SRB species, Desulfovibrio vulgaris. Duplex stainless steel samples were exposed to the medium for 13 days at 37°C at pH ranging from 4.0 to 7.4. The open-circuit potential value, sulfide level, pH and number of bacteria in the medium were recorded daily. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to study the properties of the biofilms at the end of the experiments and the corrosion behaviour of the material. Inductively coupled plasma mass spectrometry was used to measure the concentration of cations Fe, Ni, Mo, Mn, Cr in the experimental solution after 13 days. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDX) were used for surface analysis. The results showed the pH changed from acidic values set at the beginning of the experiment to approximately pH 7.5 after 5 days owing to bacterial metabolism. After 13 days, the highest iron concentration was in the solution that was initially at pH 4 accompanied by pitting on the stainless steel. Sulfur was present on all specimens but with more sulfur at pH 4 in the EDX spectra. EIS showed the film resistance of the specimen at pH 4 was much lower than at pH 7.4 which suggests the corrosion resistance of the stainless steel was better at higher pH. The results of this study suggest that the corrosion process for the first few days exposure at low pH was driven by pH in solution rather than by bacteria. The increasing pH during the course of the experiment slowed down the corrosion process of materials originally at low pH. The nature and mechanism of SRB attack on duplex stainless steel at different acidic environments are discussed.

Effect of Alkaline Artificial Seawater Environment on the Corrosion Behaviour of Duplex Stainless Steel 2205

Sulphate reducing bacteria (SRB) can be found in alkaline environments. Due to their metabolite products such as hydrogen sulphide, the corrosion behaviour of materials in alkaline environments may be affected by the presence of SRB. This study focuses on the investigation of corrosion behaviour of duplex stainless steel DSS 2205 in nutrient rich artificial seawater containing SRB species, Desulfovibrio vulgaris, at different alkaline conditions with pH range from 7 to 10. The open circuit potential value (OCP), sulphide level and pH were recorded daily. Confocal laser scanning microscopy (CLSM) was used to study the adhesion of SRB on the DSS 2205 surface. Electrochemical impedance spectroscopy (EIS) was used to study the properties of the biofilm. Potentiodynamic polarization was used to study the corrosion behaviour of material. Inductively coupled plasma mass was used to measure the concentration of cations Fe, Ni, Mo, Mn in the experimental solution after 28 days. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used for surface analysis. The results showed that D. vulgaris are active in an alkaline environment with pH 7–9. However, at pH 10, D. vulgaris activity exhibited an 8-day lag. The corrosion rate of DSS 2205 at pH 9 was higher than at other pH environments due to a higher dissolved concentration of hydrogen sulphide.

Succession of sulfur bacteria during decomposition of cyanobacterial bloom biomass in the shallow Lake Nanhu: An ex situ mesocosm study

Previous studies of the dynamics of sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) have focused on deep stratified lakes. The objective of this study is to present an in-depth investigation of the structure and dynamics of sulfur bacteria (including SRB and SOB) in the water column of shallow freshwater lakes. A cyanobacterial bloom biomass (CBB)-amended mesocosm experiment was conducted in this study, in which water was taken from a shallow eutrophic lake with sulfate levels near 40 mg L−1. Illumina sequencing was used to investigate SRB and SOB species involved in CBB decomposition and the effects of the increases in sulfate input on the water column microbial community structure. The accumulation of dissolved sulfide (∑H2S) produced by SRB during CBB decomposition stimulated the growth of SOB, and ∑H2S was then oxidized back to sulfate by SOB in the water column. Chlorobaculum sequences (the main SOB species in the study) were significantly influenced by increases in sulfate input, with relative abundance increasing approximately four-fold in treatments amended with 40 mg L−1 sulfate (referred to as 40S) when compared to the treatment without additional sulfate addition (referred to as CU). Additionally, an increase in SOB number was observed from day 26–37, concurrent with the decrease in SRB number, indicating the succession of sulfur bacteria. These findings suggest that biological sulfur oxidation and succession of sulfur bacteria occur in the water column during CBB decomposition in shallow freshwater ecosystems, and the increases in sulfate input stimulate microbial sulfur oxidation.

Microbially influenced corrosion of carbon steel in the presence of anaerobic sulphate-reducing bacteria

ABSTRACTCarbon steel is currently being considered as a candidate canister material for use in a deep geological repository of radioactive waste. Assessment of canister material corrosion through microbial activity is an important part of the safety assessment for the final repository. The aim of study was to compare and characterise the corrosion behaviour of carbon steel under sterile and non-sterile anaerobic conditions in natural groundwater containing sulphate-reducing bacteria (SRB). A molecular-biological approach was used to determine the presence and abundance changes of relevant bacterial groups. Carbon steel corrosion rates were higher in the presence of SRB compared with sterile control. EIS described the evolution of three time-constants under non-sterile conditions, while scanning electron microscopy confirmed that the carbon steel surface was covered with a two-layer biofilm. Molecular-biological analysis of the water and biofilm indicated the dominance of SRB, with Desulfomicrobium and Desulfovibrio species prevalent.

Lipid biomarker patterns of authigenic carbonates reveal fluid composition and seepage intensity at Haima cold seeps, South China Sea

Authigenic carbonates retrieved from sites ROV1 and ROV2 of the Haima hydrocarbon seeps of the South China Sea at approximately 1390 m water depth were studied using lipid biomarker analyses. Abundant molecular fossils of anaerobic methane oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB) with strong 13C-depletions (δ13C values as low as −126‰), in combination with low δ13Ccarbonate values (−42.7‰ to −36.8‰), provide evidence that anaerobic oxidation of methane (AOM) was the major process driving the precipitation of the studied seep carbonates. The extremely low δ13C values of archaeal biomarkers confirm that biogenic methane was the main carbon source, but the seepage of accessory crude oil is also suggested by the presence of unresolved complex mixtures in the hydrocarbon fractions. A suite of 13C-depleted biomarkers indicate the predominance of ANME-1/DSS consortia at both sites, which indicates that the studied carbonates formed during low to medium methane flux. Somewhat higher contents of archaeal biomarkers and their stronger 13C-depletion at site ROV2 probably reflect at least temporarily higher seepage intensities than at site ROV1. Abundant bacterial dialkyl glycerol diethers (DAGEs), revealing a large offset of their δ13C values compared to SRB-derived terminally branched fatty acids, were possibly produced by distinct SRB species other than members of the DSS cluster. The encountered hopanoids are attributed to aerobic methanotrophic bacteria based on their moderate 13C-depletion. The application of molecular fossils in combination with their compound-specific isotope signatures is an efficient tool to reconstruct the composition of seepage fluids and seepage intensities.

Application of Fruit Wastes as Cost-Effective Carbon Sources for Biological Sulphate Reduction

We conducted a study dealing with the economical application of sulphate-reducing bacteria (SRB) for the treatment of sulphate-rich wastewater. In this study, four types of frequently available fruit wastes were employed as carbon sources for economical cultivation of the SRB and consequent reduction of sulphate from artificially prepared sulphate-rich wastewater. The bacterial species employed in this study were isolated from a leading wastewater channel in Pakistan and characterized phenotypically as well as genotypically. The bacterial identities were proved after BLAST analysis and construction of phylogenetic tree. Among all of the SRB species employed for sulphate reduction, Desulfovibrio fructosovorans-HAQ2 was found as the leading sulphate reducer and reduced sulphate maximally to 29% (0.51 ± 0.02 g L−1), 76% (1.51 ± 0.07 g L−1), 41% (0.83 ± 0.02 g L−1), and 63% (1.25 ± 0.02 g L−1) using apple peelings, apple pomace, mango peelings, and watermelon rind, respectively, in a 60-day trial of anaerobic incubation. In the present study, apple pomace appeared as the most suitable carbon source only for Desulfovibrio fructosovorans-HAQ2, while any of the other three bacterial species could not reduce sulphate more than 34% using this substrate. However, on average, watermelon rind was found as the most appropriate carbon source for the cultivation of SRB and all the SRB species reduced sulphate efficiently in the range of 40–63% using this carbon source. Our findings of the present study prove the productive utility of fruit wastes for developing cost-effective and environmental-friendly remedial strategies.

Profiling of Sulfate-Reducing Bacteria in an Offshore Oil Reservoir Using Phospholipid Fatty Acid (PLFA) Biomarkers

PLFA analysis was conducted to profile microorganisms and trace sulfate-reducing bacteria (SRB) in water samples from an offshore oil reservoir. From the results of spiked phospholipid standards, more than 90% of the phospholipids were recovered before the treatment of fatty acid methyl ester (FAME) derivatization while the relative standard deviations (RSD) were below 8.0%. The water samples from the injection well and four producing wells exhibited various reducing conditions and were further subjected to PLFA analysis. Fourteen kinds of phospholipid fatty acids were detected in the five wellbores and the concentrations of total fatty acids ranged from 368.4 to 3468.9 ng/L. Possible SRB biomarkers and significant phospholipid fatty acids associated with SRB including C14:0, i-C15:0, a-C15:0, C15:0, C16:1 (cis-9), C17:0, C18:1 (cis-9), C18:1 (cis-11) and C18:0 were selected for determining the presence of SRB species and evaluating the sulfate-related microbial biomass. The possible existence of SRB genera Desulfobacter, Desulfotomaculum, Desulfovibrio, and sulfur-oxidizing bacteria (SOB) in the reservoir were proposed based on PLFA profiles. The highest biomass was found in the most reducing well where very limited SOB biomarkers were found. Results indicated that the presence of SRB and SOB species was closely associated with the redox environment of the reservoir wellbores. The species distribution patterns were interpreted to elucidate the biological souring process.