scholarly journals Syntrophs Dominate Sequences Associated with the Mercury Methylation-Related GenehgcAin the Water Conservation Areas of the Florida Everglades

2014 ◽  
Vol 80 (20) ◽  
pp. 6517-6526 ◽  
Author(s):  
Hee-Sung Bae ◽  
Forrest E. Dierberg ◽  
Andrew Ogram
Keyword(s):  
Water Conservation ◽  
Florida Everglades ◽  
Nutrient Concentrations ◽  
Mercury Methylation ◽  
Conservation Areas ◽  
Wildlife Health ◽  
Gene Encoding ◽  
Content Type ◽  
Sulfate Reducing ◽  
Aquatic Food

ABSTRACTThe mechanisms and rates of mercury methylation in the Florida Everglades are of great concern because of potential adverse impacts on human and wildlife health through mercury accumulation in aquatic food webs. We developed a new PCR primer set targetinghgcA, a gene encoding a corrinoid protein essential for Hg methylation across broad phylogenetic boundaries, and used this primer set to study the distribution ofhgcAsequences in soils collected from three sites along a gradient in sulfate and nutrient concentrations in the northern Everglades. The sequences obtained were distributed in diverse phyla, includingProteobacteria,Chloroflexi,Firmicutes, andMethanomicrobia; however,hgcAclone libraries from all sites were dominated by sequences clustering within the orderSyntrophobacteralesof theDeltaproteobacteria(49 to 65% of total sequences).dsrBmRNA sequences, representing active sulfate-reducing prokaryotes at the time of sampling, obtained from these sites were also dominated bySyntrophobacterales(75 to 89%). Laboratory incubations with soils taken from the site low in sulfate concentrations also suggested that Hg methylation activities were primarily mediated by members of the orderSyntrophobacterales, with some contribution by methanogens,Chloroflexi, iron-reducingGeobacter, and non-sulfate-reducingFirmicutesinhabiting the sites. This suggests that prokaryotes distributed within clades defined by syntrophs are the predominant group controlling methylation of Hg in low-sulfate areas of the Everglades. Any strategy for managing mercury methylation in the Everglades should consider that net mercury methylation is not limited to the action of sulfate reduction.

scholarly journals Distribution, Activities, and Interactions of Methanogens and Sulfate-Reducing Prokaryotes in the Florida Everglades

2015 ◽  
Vol 81 (21) ◽  
pp. 7431-7442 ◽  
Author(s):  
Hee-Sung Bae ◽  
M. Elizabeth Holmes ◽  
Jeffrey P. Chanton ◽  
K. Ramesh Reddy ◽  
Andrew Ogram
Keyword(s):  
Water Conservation ◽  
Specific Inhibitor ◽  
Florida Everglades ◽  
Conservation Areas ◽  
Content Type ◽  
Functional Activities ◽  
Sulfate Reducing ◽  
Nutrient Gradient ◽  
Reductase Gene ◽  
High Concentrations

ABSTRACTTo gain insight into the mechanisms controlling methanogenic pathways in the Florida Everglades, the distribution and functional activities of methanogens and sulfate-reducing prokaryotes (SRPs) were investigated in soils (0 to 2 or 0 to 4 cm depth) across the well-documented nutrient gradient in the water conservation areas (WCAs) caused by runoff from the adjacent Everglades Agricultural Area. The methyl coenzyme M reductase gene (mcrA) sequences that were retrieved from WCA-2A, an area with relatively high concentrations of SO42−(≥39 μM), indicated that methanogens inhabiting this area were broadly distributed within the ordersMethanomicrobiales,Methanosarcinales,Methanocellales,Methanobacteriales, andMethanomassiliicoccales. In more than 3 years of monitoring, quantitative PCR (qPCR) using newly designed group-specific primers revealed that the hydrogenotrophicMethanomicrobialeswere more numerous than theMethanosaetaceaeobligatory acetotrophs in SO42−-rich areas of WCA-2A, while theMethanosaetaceaewere dominant over theMethanomicrobialesin WCA-3A (with relatively low SO42−concentrations; ≤4 μM). qPCR ofdsrBsequences also indicated that SRPs are present at greater numbers than methanogens in the WCAs. In an incubation study with WCA-2A soils, addition of MoO42−(a specific inhibitor of SRP activity) resulted in increased methane production rates, lower apparent fractionation factors [αapp; defined as (amount of δ13CO2+ 1,000)/(amount of δ13CH4+ 1,000)], and higherMethanosaetaceaemcrAtranscript levels compared to those for the controls without MoO42−. These results indicate that SRPs play crucial roles in controlling methanogenic pathways and in shaping the structures of methanogen assemblages as a function of position along the nutrient gradient.

scholarly journals Periphyton and Flocculent Materials Are Important Ecological Compartments Supporting Abundant and Diverse Mercury Methylator Assemblages in the Florida Everglades

2019 ◽  
Vol 85 (13) ◽  
Author(s):  
Hee-Sung Bae ◽  
Forrest E. Dierberg ◽  
Andrew Ogram
Keyword(s):  
Environmental Concern ◽  
Peat Soil ◽  
Inorganic Mercury ◽  
Florida Everglades ◽  
Nutrient Concentrations ◽  
Content Type ◽  
Anaerobic Microorganisms ◽  
Copy Numbers ◽  
Aquatic Food ◽  
Study Sites

ABSTRACTMercury (Hg) methylation in the Florida Everglades is of great environmental concern because of its adverse effects on human and wildlife health through biomagnification in aquatic food webs. Periphyton and flocculant materials (floc) overlaying peat soil are important ecological compartments producing methylmercury (MeHg) in this ecosystem. These compartments retain higher concentrations of MeHg than did soil at study sites across nutrient and/or sulfate gradient(s). To better understand what controls Hg methylation in these compartments, the present study explored the structures and abundances of Hg methylators using geneshgcABas biomarkers. ThehgcAsequences indicated that these compartments hosted a high diversity of Hg methylators, includingDeltaproteobacteria,Chloroflexi,Firmicutes, andMethanomicrobia, with community compositions that differed between these habitats. The copy numbers ofhgcABquantified by quantitative PCR revealed that floc and soil supported higher numbers of Hg methylators than periphyton in the Everglades ecosystem. The abundance of Hg methylators was strongly positively correlated with concentrations of carbon and nutrients (e.g., phosphorus and nitrogen) according to redundancy analysis. Strong correlations were also observed among numbers of sulfate reducers, methanogens, and the dominanthgcAB-carrying groups, suggesting thathgcABwould spread primarily through the growth of those assemblages. The abundances of Hg methylators were weakly negatively correlated to MeHg concentrations, suggesting that the size of this population would not solely determine the final concentrations of MeHg in the ecological compartments studied. This study extends the knowledge regarding the distribution of diverse potential mercury methylators in different environmental compartments in a wetland of national concern.IMPORTANCEMethylmercury is a potent neurotoxin that impacts the health of humans and wildlife. Most mercury in wetlands such as the Florida Everglades enters as inorganic mercury via atmospheric deposition, some of which is transformed to the more toxic methylmercury through the activities of anaerobic microorganisms. We investigated the numbers and phylogenetic diversity ofhgcAB, genes that are linked to mercury methylation, in the soil, floc, and periphyton in areas of the Everglades with different sulfate and nutrient concentrations. Soil harbored relatively high numbers of cells capable of methylating mercury; however, little detectable methylmercury was present in soil. The greatest concentrations of methylmercury were found in floc and periphyton. The dominant methylators in those compartments included methanogens andSyntrophobacteriales. This work provides significant insight into the microbial processes that control methylation and form the basis for accumulation through the food chain in this important environment.

scholarly journals Complete Genome Sequence of Desulfobulbus oligotrophicus Prop6, an Anaerobic Deltabacterota Strain That Lacks Mercury Methylation Capability

2021 ◽  
Vol 10 (5) ◽  
Author(s):  
Peter T. Podar ◽  
Kellie Peyton ◽  
Ally Soren ◽  
Regina L. Wilpiszeski ◽  
Cynthia C. Gilmour ◽  
...  
Keyword(s):  
Sewage Sludge ◽  
Genome Sequence ◽  
Complete Genome Sequence ◽  
Complete Genome ◽  
Evolutionary Genomics ◽  
Mercury Methylation ◽  
Content Type ◽  
Sulfate Reducing ◽  
Anoxic Environments ◽  
Environmental Adaptations

ABSTRACT Desulfobulbus oligotrophicus Prop6 is a sulfate-reducing, propionate-oxidizing Deltabacterota (formerly Deltaproteobacteria) strain from sewage sludge. Desulfobulbus species are found in anoxic environments, in animal microbiota, and some produce the neurotoxin methylmercury. The 3.1-Mbp D. oligotrophicus genome sequence enables studies of diverse environmental adaptations and the evolutionary genomics of mercury methylation mechanisms.

scholarly journals Methanogens and Iron-Reducing Bacteria: the Overlooked Members of Mercury-Methylating Microbial Communities in Boreal Lakes

2018 ◽  
Vol 84 (23) ◽  
Author(s):  
Andrea G. Bravo ◽  
Sari Peura ◽  
Moritz Buck ◽  
Omneya Ahmed ◽  
Alejandro Mateos-Rivera ◽  
...  
Keyword(s):  
Microbial Communities ◽  
Lake Sediments ◽  
Aquatic Ecosystems ◽  
Sulfate Reducing Bacteria ◽  
Boreal Lakes ◽  
Mercury Methylation ◽  
Content Type ◽  
Iron Reducing Bacteria ◽  
Sulfate Reducing ◽  
Reducing Bacteria

ABSTRACTMethylmercury is a potent human neurotoxin which biomagnifies in aquatic food webs. Although anaerobic microorganisms containing thehgcAgene potentially mediate the formation of methylmercury in natural environments, the diversity of these mercury-methylating microbial communities remains largely unexplored. Previous studies have implicated sulfate-reducing bacteria as the main mercury methylators in aquatic ecosystems. In the present study, we characterized the diversity of mercury-methylating microbial communities of boreal lake sediments using high-throughput sequencing of 16S rRNA andhgcAgenes. Our results show that in the lake sediments,MethanomicrobialesandGeobacteraceaealso represent abundant members of the mercury-methylating communities. In fact, incubation experiments with a mercury isotopic tracer and molybdate revealed that only between 38% and 45% of mercury methylation was attributed to sulfate reduction. These results suggest that methanogens and iron-reducing bacteria may contribute to more than half of the mercury methylation in boreal lakes.IMPORTANCEDespite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the microorganisms identified are associated with the processing of organic matter in aquatic systems. Moreover, our results show that the well-known mercury-methylating sulfate-reducing bacteria constituted only a minor portion of the potential mercury methylators. In contrast, methanogens and iron-reducing bacteria were important contributors to methylmercury formation, highlighting their role in mercury cycling in the environment.

scholarly journals New Model for Electron Flow for Sulfate Reduction in Desulfovibrio alaskensis G20

2013 ◽  
Vol 80 (3) ◽  
pp. 855-868 ◽  
Author(s):  
Kimberly L. Keller ◽  
Barbara J. Rapp-Giles ◽  
Elizabeth S. Semkiw ◽  
Iris Porat ◽  
Steven D. Brown ◽  
...  
Keyword(s):  
Sulfate Reduction ◽  
Redox Regulation ◽  
Electron Flow ◽  
Regulation Of Gene Expression ◽  
Type I ◽  
Gene Encoding ◽  
Content Type ◽  
Sulfate Reducing ◽  
Proteomic Analyses ◽  
Physiological Tests

ABSTRACTTo understand the energy conversion activities of the anaerobic sulfate-reducing bacteria, it is necessary to identify the components involved in electron flow. The importance of the abundant type I tetraheme cytochromec3(TpIc3) as an electron carrier during sulfate respiration was questioned by the previous isolation of a null mutation in the gene encoding TpIc3,cycA, inDesulfovibrio alaskensisG20. Whereas respiratory growth of the CycA mutant with lactate and sulfate was little affected, growth with pyruvate and sulfate was significantly impaired. We have explored the phenotype of the CycA mutant through physiological tests and transcriptomic and proteomic analyses. Data reported here show that electrons from pyruvate oxidation do not reach adenylyl sulfate reductase, the enzyme catalyzing the first redox reaction during sulfate reduction, in the absence of either CycA or the type I cytochromec3:menaquinone oxidoreductase transmembrane complex, QrcABCD. In contrast to the wild type, the CycA and QrcA mutants did not grow with H2or formate and sulfate as the electron acceptor. Transcriptomic and proteomic analyses of the CycA mutant showed that transcripts and enzymes for the pathway from pyruvate to succinate were strongly decreased in the CycA mutant regardless of the growth mode. Neither the CycA nor the QrcA mutant grew on fumarate alone, consistent with the omics results and a redox regulation of gene expression. We conclude that TpIc3and the Qrc complex areD. alaskensiscomponents essential for the transfer of electrons released in the periplasm to reach the cytoplasmic adenylyl sulfate reductase and present a model that may explain the CycA phenotype through confurcation of electrons.

scholarly journals Distribution and Stability of Sulfate-Reducing Prokaryotic and Hydrogenotrophic Methanogenic Assemblages in Nutrient-Impacted Regions of the Florida Everglades

2005 ◽  
Vol 71 (5) ◽  
pp. 2695-2704 ◽  
Author(s):  
Hector Castro ◽  
Susan Newman ◽  
K. R. Reddy ◽  
Andrew Ogram
Keyword(s):  
Principal Component ◽  
Florida Everglades ◽  
Phosphorus Loading ◽  
Nutrient Concentrations ◽  
Physical Parameters ◽  
Transition Zones ◽  
Sulfate Reducing ◽  
Dissimilatory Sulfite Reductase ◽  
The Impact ◽  
Methyl Coenzyme M Reductase

ABSTRACT Although the influence of phosphorus loading on the Everglades ecosystem has received a great deal of attention, most research has targeted macro indicators, such as those based on vegetation or fauna, or chemical and physical parameters involved in biogeochemical cycles. Fewer studies have addressed the role of microorganisms, and these have mainly targeted gross informative parameters such as microbial biomass, enzymatic activities, and microbial enumerations. The objectives of this study were to characterize the dynamics of sulfate-reducing and methanogenic assemblages using terminal restriction fragment length polymorphism (T-RFLP) targeting the dissimilatory sulfite reductase (dsrA) and methyl coenzyme M reductase (mcrA) genes, respectively, and assess the impact of nutrient enrichment on microbial assemblages in the northern Everglades. T-RFLP combined with principal component analysis was a powerful technique to discriminate between soils from sites with eutrophic, transitional, and oligotrophic nutrient concentrations. dsrA T-RFLP provided a higher level of discrimination between the three sites. mcrA was a relatively weaker system to distinguish between sites, since it could not categorically discriminate between eutrophic and transition soil samples, but may be useful as an early indicator of phosphorus loading which is altering hydrogenotrophic methanogenic community in the transition zones, making them more similar to eutrophic zones. Clearly, targeting a combination of different microbial communities provides greater insight into the functioning of this ecosystem and provides useful information for understanding the relationship between eutrophication effects and microbial assemblages.

scholarly journals Methanogens Are Major Contributors to Nitrogen Fixation in Soils of the Florida Everglades

2018 ◽  
Vol 84 (7) ◽  
Author(s):  
Hee-Sung Bae ◽  
Elise Morrison ◽  
Jeffrey P. Chanton ◽  
Andrew Ogram
Keyword(s):  
Primary Productivity ◽  
Methane Production ◽  
Water Conservation ◽  
Significant Proportion ◽  
Florida Everglades ◽  
Freshwater Wetland ◽  
Rrna Genes ◽  
Content Type ◽  
N Cycle ◽  
N Limitation

ABSTRACTThe objective of this study was to investigate the interaction of the nitrogen (N) cycle with methane production in the Florida Everglades, a large freshwater wetland. This study provides an initial analysis of the distribution and expression of N-cycling genes in Water Conservation Area 2A (WCA-2A), a section of the marsh that underwent phosphorus (P) loading for many years due to runoff from upstream agricultural activities. The elevated P resulted in increased primary productivity and an N limitation in P-enriched areas. Results from quantitative real-time PCR (qPCR) analyses indicated that the N cycle in WCA-2A was dominated bynifHandnirK/S, with an increasing trend in copy numbers in P-impacted sites. ManynifHsequences (6 to 44% of the total) andnifHtranscript sequences (2 to 49%) clustered with the methanogenicEuryarchaeota, in stark contrast to the proportion of core gene sequences representingArchaea(≤0.27% of SSU rRNA genes) for the WCA-2A microbiota. Notably, archaealnifHgene transcripts were detected at all sites and comprised a significant proportion of totalnifHtranscripts obtained from the unimpacted site, indicating that methanogens are actively fixing N2. Laboratory incubations with soils taken from WCA-2A producednifHtranscripts with the production of methane from H2plus CO2and acetate as electron donors and carbon sources. Methanogenic N2fixation is likely to be an important, although largely unrecognized, route through which fixed nitrogen enters the anoxic soils of the Everglades and may have significant relevance regarding methane production in wetlands.IMPORTANCEWetlands are the most important natural sources of the greenhouse gas methane, and much of that methane emanates from (sub)tropical peatlands. Primary productivity in these peatlands is frequently limited by the availability of nitrogen or phosphorus; however, the response to nutrient limitations of microbial communities that control biogeochemical cycling critical to ecosystem function may be complex and may be associated with a range of processes, including methane production. We show that many, if not most, of the methanogens in the peatlands of the Florida Everglades possess thenifHgene and actively express it for N2fixation coupled with methanogenesis. These findings indicate that archaeal N2fixation would play crucial role in methane emissions and overall N cycle in subtropical wetlands suffering N limitation.

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