The gene pairhgcABis essential for microbial mercury methylation. Our understanding of its abunda... more The gene pairhgcABis essential for microbial mercury methylation. Our understanding of its abundance and diversity in nature is rapidly evolving. In this study we developed a new broad-range primer set forhgcAB, plus an expandedhgcABreference library, and used these to characterize Hg-methylating communities from diverse environments. We applied this new Hg-methylator database to assign taxonomy tohgcAsequences from clone, amplicon, and metagenomic datasets. We evaluated potential biases introduced in primer design, sequence length, and classification, and suggest best practices for studying Hg-methylator diversity. Our study confirms the emerging picture of an expanded diversity of HgcAB-encoding microbes in many types of ecosystems, with abundant putative mercury methylatorsNitrospiraeandChloroflexiin several new environments including salt marsh and peat soils. Other common microbes encoding HgcAB includedPhycisphaerae, Aminicenantes, Spirochaetes, andElusimicrobia. Gene abundanc...
Environmental science. Processes & impacts, Jan 5, 2018
Paddy soils from mercury (Hg)-contaminated rice fields in Guizhou, China were studied with respec... more Paddy soils from mercury (Hg)-contaminated rice fields in Guizhou, China were studied with respect to total mercury (THg) and methylmercury (MeHg) concentrations as well as Bacterial and Archaeal community composition. Total Hg (0.25-990 μg g) and MeHg (1.3-30.5 ng g) varied between samples. Pyrosequencing (454 FLX) of the hypervariable v1-v3 regions of the 16S rRNA genes showed that Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Euryarchaeota, and Crenarchaeota were dominant in all samples. The Bacterial α-diversity was higher in samples with relatively Low THg and MeHg and decreased with increasing THg and MeHg concentrations. In contrast, Archaeal α-diversity increased with increasing of MeHg concentrations but did not correlate with changes in THg concentrations. Overall, the methylation gene hgcAB copy number increased with both increasing THg and MeHg concentrations. The microbial communities at High THg and High MeHg appear to be adapted by species that are both ...
Applied and environmental microbiology, Jan 17, 2017
Neurotoxic methylmercury (MeHg) is produced by anaerobic Bacteria and Archaea possessing the gene... more Neurotoxic methylmercury (MeHg) is produced by anaerobic Bacteria and Archaea possessing the genes hgcAB, but it is unknown how organic substrate and electron acceptor availability impact the distribution and abundance of these organisms. We evaluated the impact of organic substrate amendments on mercury (Hg) methylation rates, microbial community structure, and the distribution of hgcAB+ microbes with sediments. Sediment slurries were amended with short-chain fatty acids, alcohols, or a polysaccharide. Minimal increases in MeHg were observed following lactate, ethanol and methanol amendments while a significant decrease (∼70%) was observed with cellobiose incubations. Post-incubation, microbial diversity was assessed via 16S rRNA amplicon sequencing. The presence of hgcAB+ organisms was assessed with a broad-range degenerate PCR primer set for both genes while the presence of microbes in each of the three dominant clades of methylators (Deltaproteobacteria, Firmicutes and methanoge...
Applied and environmental microbiology, Oct 15, 2016
Two genes, hgcA and hgcB, are essential for microbial mercury (Hg)-methylation. Detection and est... more Two genes, hgcA and hgcB, are essential for microbial mercury (Hg)-methylation. Detection and estimation of their abundance, in conjunction with Hg concentration, bioavailability and biogeochemistry is critical in determining potential hot spots of methylmercury (MeHg) generation in at-risk environments. We developed broad-range degenerate PCR primers spanning known hgcAB genes to determine the presence of both genes in diverse environments. These primers were tested against an extensive set of pure cultures with published genomes, including 13 Deltaproteobacteria, nine Firmicutes, and nine methanogenic Archaea A distinct PCR product at the expected size was confirmed for all hgcAB(+) strains tested via Sanger sequencing. Additionally, we developed clade-specific degenerate quantitative primers (qPCR) that targeted hgcA for each of the three dominant Hg-methylating clades. The clade-specific qPCR primers amplified hgcA from 64%, 88% and 86% of tested pure cultures of Deltaproteobact...
Proceedings of the National Academy of Sciences, 2005
The γ-proteobacterium Shewanella oneidensis strain MR-1 is a metabolically versatile organism tha... more The γ-proteobacterium Shewanella oneidensis strain MR-1 is a metabolically versatile organism that can reduce a wide range of organic compounds, metal ions, and radionuclides. Similar to most other sequenced organisms, ≈40% of the predicted ORFs in the S. oneidensis genome were annotated as uncharacterized “hypothetical” genes. We implemented an integrative approach by using experimental and computational analyses to provide more detailed insight into gene function. Global expression profiles were determined for cells after UV irradiation and under aerobic and suboxic growth conditions. Transcriptomic and proteomic analyses confidently identified 538 hypothetical genes as expressed in S. oneidensis cells both as mRNAs and proteins (33% of all predicted hypothetical proteins). Publicly available analysis tools and databases and the expression data were applied to improve the annotation of these genes. The annotation results were scored by using a seven-category schema that ranked bot...
Shewanella oneidensis MR-1 is a facultatively anaerobic bacterium capable of using soluble and in... more Shewanella oneidensis MR-1 is a facultatively anaerobic bacterium capable of using soluble and insoluble forms of manganese [Mn(III/IV)] and iron [Fe(III)] as terminal electron acceptors during anaerobic respiration. To assess the structural association of two outer membrane-associated c -type decaheme cytochromes (i.e., OmcA [SO1779] and MtrC [SO1778]) and their ability to reduce soluble Fe(III)-nitrilotriacetic acid (NTA), we expressed these proteins with a C-terminal tag in wild-type S. oneidensis and a mutant deficient in these genes (i.e., Δ omcA mtrC ). Endogenous MtrC copurified with tagged OmcA in wild-type Shewanella , suggesting a direct association. To further evaluate their possible interaction, both proteins were purified to near homogeneity following the independent expression of OmcA and MtrC in the Δ omcA mtrC mutant. Each purified cytochrome was confirmed to contain 10 hemes and exhibited Fe(III)-NTA reductase activity. To measure binding, MtrC was labeled with the ...
ABSTRACTPelosinus fermentans16S rRNA gene sequences have been reported from diverse geographical ... more ABSTRACTPelosinus fermentans16S rRNA gene sequences have been reported from diverse geographical sites since the recent isolation of the type strain. We present the genome sequence of theP. fermentanstype strain R7 (DSM 17108) and genome sequences for two new strains with different abilities to reduce iron, chromate, and uranium.
Desulfovibrio africanus strain Walvis Bay is an anaerobic sulfate-reducing bacterium capable of p... more Desulfovibrio africanus strain Walvis Bay is an anaerobic sulfate-reducing bacterium capable of producing methylmercury (MeHg), a potent human neurotoxin. The mechanism of methylation by this and other organisms is unknown. We present the 4.2-Mb genome sequence to provide further insight into microbial mercury methylation and sulfate-reducing bacteria.
The gene pairhgcABis essential for microbial mercury methylation. Our understanding of its abunda... more The gene pairhgcABis essential for microbial mercury methylation. Our understanding of its abundance and diversity in nature is rapidly evolving. In this study we developed a new broad-range primer set forhgcAB, plus an expandedhgcABreference library, and used these to characterize Hg-methylating communities from diverse environments. We applied this new Hg-methylator database to assign taxonomy tohgcAsequences from clone, amplicon, and metagenomic datasets. We evaluated potential biases introduced in primer design, sequence length, and classification, and suggest best practices for studying Hg-methylator diversity. Our study confirms the emerging picture of an expanded diversity of HgcAB-encoding microbes in many types of ecosystems, with abundant putative mercury methylatorsNitrospiraeandChloroflexiin several new environments including salt marsh and peat soils. Other common microbes encoding HgcAB includedPhycisphaerae, Aminicenantes, Spirochaetes, andElusimicrobia. Gene abundanc...
Environmental science. Processes & impacts, Jan 5, 2018
Paddy soils from mercury (Hg)-contaminated rice fields in Guizhou, China were studied with respec... more Paddy soils from mercury (Hg)-contaminated rice fields in Guizhou, China were studied with respect to total mercury (THg) and methylmercury (MeHg) concentrations as well as Bacterial and Archaeal community composition. Total Hg (0.25-990 μg g) and MeHg (1.3-30.5 ng g) varied between samples. Pyrosequencing (454 FLX) of the hypervariable v1-v3 regions of the 16S rRNA genes showed that Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Euryarchaeota, and Crenarchaeota were dominant in all samples. The Bacterial α-diversity was higher in samples with relatively Low THg and MeHg and decreased with increasing THg and MeHg concentrations. In contrast, Archaeal α-diversity increased with increasing of MeHg concentrations but did not correlate with changes in THg concentrations. Overall, the methylation gene hgcAB copy number increased with both increasing THg and MeHg concentrations. The microbial communities at High THg and High MeHg appear to be adapted by species that are both ...
Applied and environmental microbiology, Jan 17, 2017
Neurotoxic methylmercury (MeHg) is produced by anaerobic Bacteria and Archaea possessing the gene... more Neurotoxic methylmercury (MeHg) is produced by anaerobic Bacteria and Archaea possessing the genes hgcAB, but it is unknown how organic substrate and electron acceptor availability impact the distribution and abundance of these organisms. We evaluated the impact of organic substrate amendments on mercury (Hg) methylation rates, microbial community structure, and the distribution of hgcAB+ microbes with sediments. Sediment slurries were amended with short-chain fatty acids, alcohols, or a polysaccharide. Minimal increases in MeHg were observed following lactate, ethanol and methanol amendments while a significant decrease (∼70%) was observed with cellobiose incubations. Post-incubation, microbial diversity was assessed via 16S rRNA amplicon sequencing. The presence of hgcAB+ organisms was assessed with a broad-range degenerate PCR primer set for both genes while the presence of microbes in each of the three dominant clades of methylators (Deltaproteobacteria, Firmicutes and methanoge...
Applied and environmental microbiology, Oct 15, 2016
Two genes, hgcA and hgcB, are essential for microbial mercury (Hg)-methylation. Detection and est... more Two genes, hgcA and hgcB, are essential for microbial mercury (Hg)-methylation. Detection and estimation of their abundance, in conjunction with Hg concentration, bioavailability and biogeochemistry is critical in determining potential hot spots of methylmercury (MeHg) generation in at-risk environments. We developed broad-range degenerate PCR primers spanning known hgcAB genes to determine the presence of both genes in diverse environments. These primers were tested against an extensive set of pure cultures with published genomes, including 13 Deltaproteobacteria, nine Firmicutes, and nine methanogenic Archaea A distinct PCR product at the expected size was confirmed for all hgcAB(+) strains tested via Sanger sequencing. Additionally, we developed clade-specific degenerate quantitative primers (qPCR) that targeted hgcA for each of the three dominant Hg-methylating clades. The clade-specific qPCR primers amplified hgcA from 64%, 88% and 86% of tested pure cultures of Deltaproteobact...
Proceedings of the National Academy of Sciences, 2005
The γ-proteobacterium Shewanella oneidensis strain MR-1 is a metabolically versatile organism tha... more The γ-proteobacterium Shewanella oneidensis strain MR-1 is a metabolically versatile organism that can reduce a wide range of organic compounds, metal ions, and radionuclides. Similar to most other sequenced organisms, ≈40% of the predicted ORFs in the S. oneidensis genome were annotated as uncharacterized “hypothetical” genes. We implemented an integrative approach by using experimental and computational analyses to provide more detailed insight into gene function. Global expression profiles were determined for cells after UV irradiation and under aerobic and suboxic growth conditions. Transcriptomic and proteomic analyses confidently identified 538 hypothetical genes as expressed in S. oneidensis cells both as mRNAs and proteins (33% of all predicted hypothetical proteins). Publicly available analysis tools and databases and the expression data were applied to improve the annotation of these genes. The annotation results were scored by using a seven-category schema that ranked bot...
Shewanella oneidensis MR-1 is a facultatively anaerobic bacterium capable of using soluble and in... more Shewanella oneidensis MR-1 is a facultatively anaerobic bacterium capable of using soluble and insoluble forms of manganese [Mn(III/IV)] and iron [Fe(III)] as terminal electron acceptors during anaerobic respiration. To assess the structural association of two outer membrane-associated c -type decaheme cytochromes (i.e., OmcA [SO1779] and MtrC [SO1778]) and their ability to reduce soluble Fe(III)-nitrilotriacetic acid (NTA), we expressed these proteins with a C-terminal tag in wild-type S. oneidensis and a mutant deficient in these genes (i.e., Δ omcA mtrC ). Endogenous MtrC copurified with tagged OmcA in wild-type Shewanella , suggesting a direct association. To further evaluate their possible interaction, both proteins were purified to near homogeneity following the independent expression of OmcA and MtrC in the Δ omcA mtrC mutant. Each purified cytochrome was confirmed to contain 10 hemes and exhibited Fe(III)-NTA reductase activity. To measure binding, MtrC was labeled with the ...
ABSTRACTPelosinus fermentans16S rRNA gene sequences have been reported from diverse geographical ... more ABSTRACTPelosinus fermentans16S rRNA gene sequences have been reported from diverse geographical sites since the recent isolation of the type strain. We present the genome sequence of theP. fermentanstype strain R7 (DSM 17108) and genome sequences for two new strains with different abilities to reduce iron, chromate, and uranium.
Desulfovibrio africanus strain Walvis Bay is an anaerobic sulfate-reducing bacterium capable of p... more Desulfovibrio africanus strain Walvis Bay is an anaerobic sulfate-reducing bacterium capable of producing methylmercury (MeHg), a potent human neurotoxin. The mechanism of methylation by this and other organisms is unknown. We present the 4.2-Mb genome sequence to provide further insight into microbial mercury methylation and sulfate-reducing bacteria.
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Papers by Dwayne Elias