scholarly journals Complex Microbial Communities Drive Iron and Sulfur Cycling in Arctic Fjord Sediments

2019 ◽  
Vol 85 (14) ◽  
Author(s):  
J. Buongiorno ◽  
L. C. Herbert ◽  
L. M. Wehrmann ◽  
A. B. Michaud ◽  
K. Laufer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Primary Production ◽  
Sulfate Reduction ◽  
The Arctic ◽  
Sulfur Cycling ◽  
Glacial Retreat ◽  
Sulfate Reducing ◽  
Glacial Runoff ◽  
Sulfate Reduction Rates ◽  
Fjord Sediments

ABSTRACTGlacial retreat is changing biogeochemical cycling in the Arctic, where glacial runoff contributes iron for oceanic shelf primary production. We hypothesize that in Svalbard fjords, microbes catalyze intense iron and sulfur cycling in low-organic-matter sediments. This is because low organic matter limits sulfide generation, allowing iron mobility to the water column instead of precipitation as iron monosulfides. In this study, we tested this with high-depth-resolution 16S rRNA gene libraries in the upper 20 cm at two sites in Van Keulenfjorden, Svalbard. At the site closer to the glaciers, iron-reducingDesulfuromonadales, iron-oxidizingGallionellaandMariprofundus, and sulfur-oxidizingThiotrichalesandEpsilonproteobacteriawere abundant above a 12-cm depth. Below this depth, the relative abundances of sequences for sulfate-reducingDesulfobacteraceaeandDesulfobulbaceaeincreased. At the outer station, the switch from iron-cycling clades to sulfate reducers occurred at shallower depths (∼5 cm), corresponding to higher sulfate reduction rates. Relatively labile organic matter (shown by δ13C and C/N ratios) was more abundant at this outer site, and ordination analysis suggested that this affected microbial community structure in surface sediments. Network analysis revealed more correlations between predicted iron- and sulfur-cycling taxa and with uncultured clades proximal to the glacier. Together, these results suggest that complex microbial communities catalyze redox cycling of iron and sulfur, especially closer to the glacier, where sulfate reduction is limited due to low availability of organic matter. Diminished sulfate reduction in upper sediments enables iron to flux into the overlying water, where it may be transported to the shelf.IMPORTANCEGlacial runoff is a key source of iron for primary production in the Arctic. In the fjords of the Svalbard archipelago, glacial retreat is predicted to stimulate phytoplankton blooms that were previously restricted to outer margins. Decreased sediment delivery and enhanced primary production have been hypothesized to alter sediment biogeochemistry, wherein any free reduced iron that could potentially be delivered to the shelf will instead become buried with sulfide generated through microbial sulfate reduction. We support this hypothesis with sequencing data that showed increases in the relative abundance of sulfate reducing taxa and sulfate reduction rates with increasing distance from the glaciers in Van Keulenfjorden, Svalbard. Community structure was driven by organic geochemistry, suggesting that enhanced input of organic material will stimulate sulfate reduction in interior fjord sediments as glaciers continue to recede.

Interactions between filamentous sulfur bacteria, sulfate reducing bacteria and poly-P accumulating bacteria in anaerobic-oxic activated sludge from a municipal plant

1998 ◽  
Vol 37 (4-5) ◽  
pp. 599-603 ◽  
Author(s):  
Ryoko Yamamoto-Ikemoto ◽  
Saburo Matsui ◽  
Tomoaki Komori ◽  
Edja. Kofi. Bosque-Hamilton
Keyword(s):  
Activated Sludge ◽  
Sulfate Reduction ◽  
Reduction Rate ◽  
Sulfate Reducing Bacteria ◽  
Sulfate Reduction Rate ◽  
Filamentous Bulking ◽  
Sulfate Reducing ◽  
Sulfur Bacteria ◽  
Sulfate Reduction Rates ◽  
Reducing Bacteria

The interactions between filamentous sulfur bacteria (FSB), sulfate reducing bacteria (SRB) and poly-P accumulating bacteria (PAB) in the activated sludge of a municipal plant operated under anaerobic-oxic conditions were examined in batch experiments using return sludge (RAS) and settled sewage. Phosphate release and sulfate reduction occurred simultaneously under anaerobic conditions. SRB were more sensitive to temperature changes than PAB. SRB played an important role in the decomposition of propionate to acetate. When the sulfate reduction rates were high, there was a tendency for the maximum release of phosphate also to be high. This was explained by the fact that PAB utilized the acetate produced by SRB. Sulfur oxidizing bacteria were sensitive to temperature change. When the sulfate reduction rate was high, the sulfide oxidizing rate was also high and filamentous bulking occurred. The results showed that sulfate reduction was a cause of filamentous bulking due to Type 021N that could utilize reduced sulfur.

scholarly journals Sulfur Isotope Enrichment during Maintenance Metabolism in the Thermophilic Sulfate-Reducing Bacterium Desulfotomaculum putei

2009 ◽  
Vol 75 (17) ◽  
pp. 5621-5630 ◽  
Author(s):  
Mark M. Davidson ◽  
M. E. Bisher ◽  
Lisa M. Pratt ◽  
Jon Fong ◽  
Gordon Southam ◽  
...  
Keyword(s):  
Sulfate Reduction ◽  
Batch Culture ◽  
Marine Sediments ◽  
Maintenance Phase ◽  
Laboratory Culture ◽  
Specific Rate ◽  
Culture Vessel ◽  
Isotope Enrichment ◽  
Sulfate Reducing ◽  
Sulfate Reduction Rates

ABSTRACT Values of Δ34S ( \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({=}{\delta}^{34}S_{HS}{-}{\delta}^{34}S_{SO_{4}}\) \end{document} , where δ34SHS and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\delta}^{34}S_{SO_{4}}\) \end{document} indicate the differences in the isotopic compositions of the HS− and SO4 2− in the eluent, respectively) for many modern marine sediments are in the range of −55 to −75‰, much greater than the −2 to −46‰ ε34S (kinetic isotope enrichment) values commonly observed for microbial sulfate reduction in laboratory batch culture and chemostat experiments. It has been proposed that at extremely low sulfate reduction rates under hypersulfidic conditions with a nonlimited supply of sulfate, isotopic enrichment in laboratory culture experiments should increase to the levels recorded in nature. We examined the effect of extremely low sulfate reduction rates and electron donor limitation on S isotope fractionation by culturing a thermophilic, sulfate-reducing bacterium, Desulfotomaculum putei, in a biomass-recycling culture vessel, or “retentostat.” The cell-specific rate of sulfate reduction and the specific growth rate decreased progressively from the exponential phase to the maintenance phase, yielding average maintenance coefficients of 10−16 to 10−18 mol of SO4 cell−1 h−1 toward the end of the experiments. Overall S mass and isotopic balance were conserved during the experiment. The differences in the δ34S values of the sulfate and sulfide eluting from the retentostat were significantly larger, attaining a maximum Δ34S of −20.9‰, than the −9.7‰ observed during the batch culture experiment, but differences did not attain the values observed in marine sediments.

Benthic Fe-cycling in fjord sediments enhances the reactivity of glacially derived Fe in Arctic fjords of Svalbard

2020 ◽  
Author(s):  
Katja Laufer ◽  
Alexander Michaud ◽  
Hans Røy ◽  
Bo Barker Jørgensen
Keyword(s):  
Water Column ◽  
Time Course ◽  
Redox Cycling ◽  
Marine Phytoplankton ◽  
Glacial Retreat ◽  
Tidewater Glaciers ◽  
Glacial Runoff ◽  
Bedrock Lithology ◽  
The Impact ◽  
Fjord Sediments

<p>Glacial runoff is a significant source of Fe to high-latitude marine environments. The amount and characteristics of glacially derived Fe depends on bedrock lithology, glacial comminution as well as glacier type. Because much of the Fe that comes from glaciers is in the particulate phase or will become particulate once in contact with saline and oxic fjord water, much of the glacial Fe ends up in fjord sediments in close proximity to the glaciers. Within these sediments, the glacially derived Fe undergoes redox-cycling driven by indirect (abiotic reaction with metabolic products, such as hydrogen sulfide) and direct interactions with microorganisms. This redox-cycling has the potential to alter the characteristics of the glacially derived Fe and thereby also its fate, for example if it is buried in the sediment or exported to the water column.</p><p>We investigated the amount and reactivity of Fe(III) minerals from the meltwater plume, meltwater streams, icebergs, and sediments at stations with increasing distance from the glacier in three different fjords on the west coast of Spitsbergen, Svalbard. Two of the fjords have large tidewater- glaciers at their head and possess differing bedrock lithology (Kongsfjorden and Lilliehöökfjorden). The third fjord, Dicksonfjorden, has land-terminating glaciers with a bedrock lithology similar to the glaciers at the head of Kongsfjorden, thus providing insight into the impact of glacial retreat on benthic biogeochemical processes. Results from sequential and time-course extractions showed that Fe(III)-mineral reactivity increased with distance from the glacier fronts and decreased with sediment depth at each station in all three fjords. Fe(III)-oxide reactivity from different glacial sources (meltwater plume and iceberg material from tidewater glaciers and meltwater stream material from land-terminating glaciers) differed based on source type and Fe(III) from all glacial sources was generally less reactive compared to surficial sediments distal to the glacier front. While the general trends were the same for all three fjords, based on pore water profiles of dissolved Fe, we found a lower potential for Fe-export to the water column when only land-terminating glaciers were present. This difference highlights that glacial retreat potentially impacts the function of fjord sediments as a source of Fe to the water column. We conclude that glacial runoff supplies large quantities of Fe minerals to fjord sediments, but benthic recycling of Fe by microorganisms transforms the relatively unreactive glacially-derived Fe(III)-oxides to a more reactive form. Microbially driven recycling of reactive Fe(III)-oxides in fjord sediments may play a role in liberating Fe to the water column, predominantly at the mouth of the fjord, and might represent an unquantified source of Fe to Fe-limited marine phytoplankton.</p>

scholarly journals Glacial runoff promotes deep burial of sulfur cycling-associated microorganisms in marine sediments

2019 ◽  
Author(s):  
Claus Pelikan ◽  
Marion Jaussi ◽  
Kenneth Wasmund ◽  
Marit-Solveig Seidenkrantz ◽  
Christof Pearce ◽  
...  
Keyword(s):  
Organic Matter ◽  
Microbial Community ◽  
Community Assembly ◽  
Microbial Community Composition ◽  
Sulfur Cycling ◽  
Sedimentation Rates ◽  
Sediment Depth ◽  
Glacial Runoff ◽  
Microbial Community Assembly ◽  
Sediment Age

AbstractMarine fjords with active glacier outlets are hot spots for organic matter burial in the sediments and subsequent microbial mineralization, and will be increasingly important as climate warming causes more rapid glacial melt. Here, we investigated controls on microbial community assembly in sub-arctic glacier-influenced (GI) and non-glacier-influenced (NGI) marine sediments in the Godthåbsfjord region, south-western Greenland. We used a correlative approach integrating 16S rRNA gene and dissimilatory sulfite reductase (dsrB) amplicon sequence data over six meters of depth with biogeochemistry, sulfur-cycling activities, and sediment ages. GI sediments were characterized by comparably high sedimentation rates and had ‘young’ sediment ages of <500 years even at 6 m sediment depth. In contrast, NGI stations reached ages of approximately 10,000 years at these depths. Sediment age-depth relationships, sulfate reduction rates, and C/N ratios were strongly correlated with differences in microbial community composition between GI and NGI sediments, indicating that age and diagenetic state were key drivers of microbial community assembly in subsurface sediments. Similar bacterial and archaeal communities were present in the surface sediments of all stations, whereas only in GI sediments were many surface taxa also abundant through the whole sediment core. The relative abundance of these taxa, including diverseDesulfobacteraceaemembers, correlated positively with sulfate reduction rates, indicating their active contributions to sulfur-cycling processes. In contrast, other surface community members, such asDesulfatiglans, AtribacteriaandChloroflexi, survived the slow sediment burial at NGI stations and dominated in the deepest sediment layers. These taxa are typical for the energy-limited marine deep biosphere and their relative abundances correlated positively with sediment age. In conclusion, our data suggests that high rates of sediment accumulation caused by glacier runoff and associated changes in biogeochemistry, promote persistence of sulfur-cycling activity and burial of a larger fraction of the surface microbial community into the deep subsurface.Contribution to the Field StatementIn most coastal marine sediments organic matter turnover and total energy flux are highest at the surface and decrease significantly with increasing sediment depth, causing depth-dependent changes in the microbial community composition. Glacial runoff in arctic and subarctic fjords alters the composition of the microbial community at the surface, mainly due to different availabilities of organic matter and metals. Here we show that glacial runoff also modifies microbial community assembly with sediment depth. Sediment age was a key driver of microbial community composition in six-meter-long marine sediment cores from the Godthåbsfjord region, south-western Greenland. High sedimentation rates at glacier-influenced sediment stations enabled a complex community of sulfur-cycling-associated microorganisms to continuously thrive at high relative abundances from the surface into the sediment subsurface. These communities consisted of putative fermenters, sulfate reducers and sulfur oxidizers, which likely depended on high metal concentrations in the relatively young, glacier-influenced sediments. In non-glacier-influenced sediments with lower sedimentation rates, these sulfur-cycling-associated microorganisms were only present near the surface. With increasing sediment depth these surface microorganisms were largely replaced by other surface microorganisms that positively correlated with sediment age and belong to known taxa of the energy-limited, marine deep biosphere.

scholarly journals Diversity decoupled from sulfur isotope fractionation in a sulfate reducing microbial community

2019 ◽  
Author(s):  
Jesse Colangelo ◽  
Claus Pelikan ◽  
Craig W. Herbold ◽  
Ianina Altshuler ◽  
Alexander Loy ◽  
...  
Keyword(s):  
Microbial Community ◽  
Microbial Ecology ◽  
Sulfate Reduction ◽  
Isotope Fractionation ◽  
Sulfur Isotopes ◽  
List Type ◽  
Natural Habitats ◽  
Sulfate Reducing ◽  
Sulfate Reduction Rates

AbstractThe extent of fractionation of sulfur isotopes by sulfate reducing microbes is dictated by genomic and environmental factors. A greater understanding of species-specific fractionations may better inform interpretation of sulfur isotopes preserved in the rock record. To examine whether gene diversity influences net isotopic fractionation in situ, we assessed environmental chemistry, sulfate reduction rates, diversity of putative sulfur metabolizing organisms by 16S rRNA and dissimilatory sulfite reductase (dsrB) gene amplicon sequencing, and net fractionation of sulfur isotopes along a sediment transect of a hypersaline Arctic spring. In situ sulfate reduction rates yielded minimum cell-specific sulfate reduction rates <0.3 x 10−15 moles cell−1 day−1. Neither 16S rRNA nor dsrB diversity indices correlated with relatively constant (38 to 45‰) net isotope fractionation (ε34Ssulfide−sulfate). Measured ε34S values could be reproduced in a mechanistic fractionation model if 1-2% of the microbial community (10-60% of Deltaproteobacteria) were engaged in sulfate respiration, indicating heterogeneous respiratory activity within sulfate-metabolizing populations. This model indicated enzymatic kinetic diversity of Apr was more likely to correlate with sulfur fractionation than DsrB. We propose that, above a threshold alpha diversity value, the influence of the specific composition of the microbial community responsible for generating an isotope signal is overprinted by the control exerted by environmental variables on microbial physiology.Subject categoriesIntegrated genomics and post-genomics approaches in microbial ecologyMicrobial ecology and functional diversity of natural habitats

Genomic variation of microbial populations on a continuous 10,000-year sediment sequence from Lake Cadagno (Piora Valley, Switzerland)

2021 ◽  
Author(s):  
Paula Catalina Rodriguez Ramirez ◽  
Jasmine Berg ◽  
Longhui Deng ◽  
Hendrik Vogel ◽  
Mark A. Lever ◽  
...  
Keyword(s):  
16S Rrna ◽  
16S Rrna Gene ◽  
Sulfate Reduction ◽  
Microbial Populations ◽  
Gene Copy ◽  
Sulfur Cycling ◽  
Rrna Gene ◽  
Sediment Layer ◽  
Metagenomic Sequencing ◽  
Sulfate Reducing

&lt;p&gt;Lake Cadagno is a meromictic Alpine lake located in the Piora Valley, Switzerland. In 2019, a 10,000-year (10 m)sediment sequence was collected and found to contain three main lithological units: glacial sediment deposited under oxic conditions; a Mn-rich and organic-matter-rich sediment layer deposited during the transition from an oxic late-glacial lake to the onset of anoxia, and dark, sulfidic sediments deposited during the period of euxinia to the present. This study investigates the relationships between the physical-chemical properties and microorganisms of the sediment sequenceusing genome-resolved and targeted metagenomics.&amp;#160; &amp;#160;&lt;/p&gt;&lt;p&gt;Results show that 16S rRNA gene abundance peaks in upper 1-32 cm of the sediment core (10&lt;sup&gt;8&lt;/sup&gt; copies per gram of sediment) and decreases with depth. The abundance of a marker gene for sulfate reduction, dsrB, is positively correlated to 16S rRNA gene copy numbers, decreasing with depth from approximately 10&lt;sup&gt;8&lt;/sup&gt; copies per gram of sediment in the top 30 cm to 10&lt;sup&gt;4&lt;/sup&gt; gene copies per gram of sediment at 900 cm below the sediment depth.&amp;#160; These results suggest that sulfate-reducing microbial communities in surface sediments harvest the bioavailable oxidized sulfur inorganic species. In contrast, the presence of sulfate-reducing genes in sediments with sulfate concentrations below detection may indicate the engagement of microbial populations in sulfur cycling using alternative metabolic strategies (e.g. secondary fermentation).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Moreover, a clear differentiation between surface and deep sediment communities is observed. Sequencing of dsrB amplicons show a decrease in dsrB sequence richness with depth and sediment age. A clear transition from a surface section dominated (&gt;80% relative abundance) by Deltaproteobacteria-related dsrB sequences from well-studied groups, to a deeper section below 40 cm dominated by a group of unclassified dsrB sequences most likely related to Firmicutes or Chloroflexi is also observed. The identity of these unclassified dsrB sequences will be determined by genome-resolved metagenomic sequencing (currently in progress). Furthermore, these analyses will give information on the presence of complete sulfate-reduction pathways and/or genes related to sulfur cycling in these microbial groups. By reconstructing the genomes of sulfate reducers and other microbial populations throughout the core, we will investigate whether there are genomic changes associated with the main geochemical trends. This work will enable us to assess the influence of a changing lake with the evolution of sediment-dwelling prokaryotic populations over thousands of years.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Organic matter composition and sulfate reduction rates in sediments off Chile

2000 ◽  
Vol 31 (5) ◽  
pp. 351-361 ◽  
Author(s):  
Carsten J. Schubert ◽  
Timothy G. Ferdelman ◽  
Bettina Strotmann
Keyword(s):  
Organic Matter ◽  
Sulfate Reduction ◽  
Organic Matter Composition ◽  
Sulfate Reduction Rates

Improved Most-Probable-Number Method To Detect Sulfate-Reducing Bacteria with Natural Media and a Radiotracer

1998 ◽  
Vol 64 (5) ◽  
pp. 1700-1707 ◽  
Author(s):  
Flemming Vester ◽  
Kjeld Ingvorsen
Keyword(s):  
Sulfate Reduction ◽  
Environmental Samples ◽  
Sulfate Reducing Bacteria ◽  
Most Probable Number ◽  
Probable Number ◽  
Sulfate Reducing ◽  
Sulfate Reduction Rates ◽  
Synthetic Media ◽  
Reducing Bacteria ◽  
Natural Media

ABSTRACT A greatly improved most-probable-number (MPN) method for selective enumeration of sulfate-reducing bacteria (SRB) is described. The method is based on the use of natural media and radiolabeled sulfate (35SO4 2−). The natural media used consisted of anaerobically prepared sterilized sludge or sediment slurries obtained from sampling sites. The densities of SRB in sediment samples from Kysing Fjord (Denmark) and activated sludge were determined by using a normal MPN (N-MPN) method with synthetic cultivation media and a tracer MPN (T-MPN) method with natural media. The T-MPN method with natural media always yielded significantly higher (100- to 1,000-fold-higher) MPN values than the N-MPN method with synthetic media. The recovery of SRB from environmental samples was investigated by simultaneously measuring sulfate reduction rates (by a35S-radiotracer method) and bacterial counts by using the T-MPN and N-MPN methods, respectively. When bacterial numbers estimated by the T-MPN method with natural media were used, specific sulfate reduction rates (qSO4 2−) of 10−14to 10−13 mol of SO4 2−cell−1 day−1 were calculated, which is within the range of qSO4 2− values previously reported for pure cultures of SRB (10−15 to 10−14 mol of SO4 2− cell−1day−1). qSO4 2− values calculated from N-MPN values obtained with synthetic media were several orders of magnitude higher (2 � 10−10 to 7 � 10−10 mol of SO4 2−cell−1 day−1), showing that viable counts of SRB were seriously underestimated when standard enumeration media were used. Our results demonstrate that the use of natural media results in significant improvements in estimates of the true numbers of SRB in environmental samples.

scholarly journals On the Occurrence of Anoxic Microniches, Denitrification, and Sulfate Reduction in Aerated Activated Sludge

1999 ◽  
Vol 65 (9) ◽  
pp. 4189-4196 ◽  
Author(s):  
Andreas Schramm ◽  
Cecilia M. Santegoeds ◽  
Helle K. Nielsen ◽  
Helle Ploug ◽  
Michael Wagner ◽  
...  
Keyword(s):  
Activated Sludge ◽  
Sulfate Reduction ◽  
Laser Scanning ◽  
Three Dimensional ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Sulfate Reducing ◽  
Dissimilatory Sulfite Reductase ◽  
Sulfate Reduction Rates ◽  
Anoxic Zones

ABSTRACT A combination of different methods was applied to investigate the occurrence of anaerobic processes in aerated activated sludge. Microsensor measurements (O2, NO2 −, NO3 −, and H2S) were performed on single sludge flocs to detect anoxic niches, nitrate reduction, or sulfate reduction on a microscale. Incubations of activated sludge with15NO3 − and35SO4 2− were used to determine denitrification and sulfate reduction rates on a batch scale. In four of six investigated sludges, no anoxic zones developed during aeration, and consequently denitrification rates were very low. However, in two sludges anoxia in flocs coincided with significant denitrification rates. Sulfate reduction could not be detected in any sludge in either the microsensor or the batch investigation, not even under short-term anoxic conditions. In contrast, the presence of sulfate-reducing bacteria was shown by fluorescence in situ hybridization with 16S rRNA-targeted oligonucleotide probes and by PCR-based detection of genes coding for the dissimilatory sulfite reductase. A possible explanation for the absence of anoxia even in most of the larger flocs might be that oxygen transport is not only diffusional but enhanced by advection, i.e., facilitated by flow through pores and channels. This possibility is suggested by the irregularity of some oxygen profiles and by confocal laser scanning microscopy of the three-dimensional floc structures, which showed that flocs from the two sludges in which anoxic zones were found were apparently denser than flocs from the other sludges.

Low Temperature Sulfate Reduction for AMD Treatment

2009 ◽  
Vol 71-73 ◽  
pp. 553-556
Author(s):  
Laura M. Nevatalo ◽  
Hannele Auvinen ◽  
Martijn F.M. Bijmans ◽  
Anna H. Kaksonen ◽  
Piet N.L. Lens ◽  
...  
Keyword(s):  
Low Temperature ◽  
Temperature Gradient ◽  
Sulfate Reduction ◽  
Mine Drainage ◽  
Enrichment Culture ◽  
Rrna Gene ◽  
Sulfate Reducing ◽  
Sulfate Reduction Rates ◽  
Reducing Bacteria ◽  
Gas Lift

The amenability of sulfate reduction at low temperature for the treatment of acid mine drainage in arctic areas was investigated with three reactor experiments. The aim of these studies was to assess the potential and determine rates of sulfate reduction at 9oC with formic acid and hydrogen as electron donors. Three different bench-scale reactor configurations were tested: fluidized-bed reactor, membrane bioreactor and gas-lift bioreactor. The reactors were inoculated with a low temperature enrichment culture of sulfate-reducing bacteria. The temperature range of sulfate reduction was studied with a temperature gradient assay. The microbial community structure of the reactors was analyzed using polymerase chain reaction - denaturating gel gradient electrophoresis (PCR-DGGE) with universal 16S rRNA gene primers and SRB specific dsrB primers. The stable sulfate reduction rates at 9oC in all the reactors ranged from 0.6 to 1.4 g SO42- L-1 d-1. The temperature gradient assay supported also by the PCR-DGGE sequence profiling indicated that the low temperature enrichment was dominated by a psychrotolerant mesophilic Desulfomicrobium sp. having their maximal sulfide production rate at 31oC.

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