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Genome sequence of Desulfitobacterium hafniense DCB-2, a Gram-positive anaerobe capable of dehalogenation and metal reduction.

Kim SH, Harzman C, Davis JK, Hutcheson R, Broderick JB, Marsh TL, Tiedje JM - BMC Microbiol. (2012)

Bottom Line: In addition, it contained genes for 53 molybdopterin-binding oxidoreductases, 19 flavoprotein paralogs of the fumarate reductase, and many other FAD/FMN-binding oxidoreductases, proving the cell's versatility in both adaptive and reductive capacities.Together with the ability to form spores, the presence of the CO2-fixing Wood-Ljungdahl pathway and the genes associated with oxygen tolerance add flexibility to the cell's options for survival under stress.D. hafniense DCB-2's genome contains genes consistent with its abilities for dehalogenation, metal reduction, N2 and CO2 fixation, anaerobic respiration, oxygen tolerance, spore formation, and biofilm formation which make this organism a potential candidate for bioremediation at contaminated sites.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Microbial Ecology, Michigan State University, East Lansing, MI, USA. kimsang8@msu.edu

ABSTRACT

Background: The genome of the Gram-positive, metal-reducing, dehalorespiring Desulfitobacterium hafniense DCB-2 was sequenced in order to gain insights into its metabolic capacities, adaptive physiology, and regulatory machineries, and to compare with that of Desulfitobacterium hafniense Y51, the phylogenetically closest strain among the species with a sequenced genome.

Results: The genome of Desulfitobacterium hafniense DCB-2 is composed of a 5,279,134-bp circular chromosome with 5,042 predicted genes. Genome content and parallel physiological studies support the cell's ability to fix N2 and CO2, form spores and biofilms, reduce metals, and use a variety of electron acceptors in respiration, including halogenated organic compounds. The genome contained seven reductive dehalogenase genes and four nitrogenase gene homologs but lacked the Nar respiratory nitrate reductase system. The D. hafniense DCB-2 genome contained genes for 43 RNA polymerase sigma factors including 27 sigma-24 subunits, 59 two-component signal transduction systems, and about 730 transporter proteins. In addition, it contained genes for 53 molybdopterin-binding oxidoreductases, 19 flavoprotein paralogs of the fumarate reductase, and many other FAD/FMN-binding oxidoreductases, proving the cell's versatility in both adaptive and reductive capacities. Together with the ability to form spores, the presence of the CO2-fixing Wood-Ljungdahl pathway and the genes associated with oxygen tolerance add flexibility to the cell's options for survival under stress.

Conclusions: D. hafniense DCB-2's genome contains genes consistent with its abilities for dehalogenation, metal reduction, N2 and CO2 fixation, anaerobic respiration, oxygen tolerance, spore formation, and biofilm formation which make this organism a potential candidate for bioremediation at contaminated sites.

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Physical map of the reductive dehalogenase (rdh) operons in D. hafniense DCB-2. The catalytic RDase subunit genes, rdhA1 through rdhA7, are colored black, and the docking protein genes, rdhB1 through rdhB7, are colored yellow. Other RDase accessory genes are colored green. Disruptions of rdhA2 and rdhA7 by an insertion of a transposase gene (tra) and by nonsense mutation, respectively, are indicated. The RDase genes, for which transcription was detected by microarrays are indicated with arrows and substrate names with fold induction. All the substrates indicated above the rdhA2, rdhA3, and rdhA6 genes induced their corresponding gene expression in northern hybridization experiments. 3Cl-4OH-BA; 3-chloro-4-hydroxybenzoate, o-BP; ortho-bromophenol, 3,5-DCP; 3,5-dichlorophenol.
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Figure 5: Physical map of the reductive dehalogenase (rdh) operons in D. hafniense DCB-2. The catalytic RDase subunit genes, rdhA1 through rdhA7, are colored black, and the docking protein genes, rdhB1 through rdhB7, are colored yellow. Other RDase accessory genes are colored green. Disruptions of rdhA2 and rdhA7 by an insertion of a transposase gene (tra) and by nonsense mutation, respectively, are indicated. The RDase genes, for which transcription was detected by microarrays are indicated with arrows and substrate names with fold induction. All the substrates indicated above the rdhA2, rdhA3, and rdhA6 genes induced their corresponding gene expression in northern hybridization experiments. 3Cl-4OH-BA; 3-chloro-4-hydroxybenzoate, o-BP; ortho-bromophenol, 3,5-DCP; 3,5-dichlorophenol.

Mentions: Desulfitobacterium and Dehalococcoides constitute most of the dehalorespiring bacteria isolates to date. These bacteria can use halogenated compounds such as chlorophenols and chloroethenes as terminal electron acceptors and acquire energy via anaerobic respiration (dehalorespiration). In this process, the halogenated compounds produce halide atoms. D. hafniense DCB-2 was isolated using 2,4,6-trichlorophenol (2,4,6-TCP) [4] as its electron acceptor, and also reduces 2,4,5-TCP, 2,4-dichlorophenol (2,4-DCP), 2,5-DCP, 3-chloro-4-hydroxyphenylacetate (3Cl-4OH-PA), tetrachlorohydroquinone (TCHQ), 2,3,5,6-tetrachloro-4-methoxyphenol (TCMP), and pentachlorophenol (PCP) [4,5,53-55]. A slight conversion of tetrachloroethene (PCE) to trichloroethene (TCE) was reported by resting cells pregrown with 3Cl-4OH-PA [53]. In the DCB-2 genome, seven RDase genes were identified (Figure 4) versus two in D. hafniense Y51, one of which encodes a PCE RDase (DSY2839, Rdh2 in Figure 1) as it was shown to dechlorinate PCE to cis-1,2-dichloroethene via trichloroethene [8,10]. Among the seven DCB-2 RDase genes, rdhA2 and rdhA7 (Dhaf_0696 and Dhaf_2620) appeared to be non-functional since the genes are interrupted by a transposase gene and nonsense mutation, respectively (Figure 4). BLAST analysis of the five intact genes suggested that four of the genes code for o-chlorophenol RDases (rdhA1, rdhA4, rdhA5, rdhA6) and rdhA3 is highly homologous (66.7% identity in amino acid sequence) to the pce gene of Y51 (DSY2839). The operon harboring rdhA6 contains a complete gene set for reductive dehalogenation and is similar in gene organization (cprTKZEBACD) to the one in D. dehalogenans that is inducible by 3-Cl-4OH-PA [56]. RdhB is an integral membrane protein and acts as a membrane anchor for RDase. RdhC and RdhK belong to the NirI/NosR and CRP-FNR families of transcriptional regulatory proteins. RdhD and RdhE are predicted to be molecular chaperones and RdhT is a homolog to trigger factor folding catalysts. Previously, RDase encoded by rdhA6 of DCB-2 was shown to dechlorinate 3-Cl-4OH-PA [57]. We observed, via northern blot analysis, that this gene was also induced in transcription by other halogenated substrates: 3-chloro-4-hydroxybenzoate (3Cl-4OH-BA) and ortho-bromophenol (o-BP) (summarized in Figure 5). In the same experiment, induction by 3,5-dichlorophenol (3,5-DCP) was observed for rdhA3 which was considered to encode a chloroethene RDase. Our cDNA microarray results, obtained from independently prepared samples, were consistent for the high induction of rdhA6 by 3Cl-4OH-BA (70-fold) and of rdhA3 by 3,5-DCP (32-fold). However, we also observed some inconsistent results between the homology data and the expression data, especially when the level of gene expression was low (e.g. o-BP on rdhA3 and rdhA6 in Figure 5).


Genome sequence of Desulfitobacterium hafniense DCB-2, a Gram-positive anaerobe capable of dehalogenation and metal reduction.

Kim SH, Harzman C, Davis JK, Hutcheson R, Broderick JB, Marsh TL, Tiedje JM - BMC Microbiol. (2012)

Physical map of the reductive dehalogenase (rdh) operons in D. hafniense DCB-2. The catalytic RDase subunit genes, rdhA1 through rdhA7, are colored black, and the docking protein genes, rdhB1 through rdhB7, are colored yellow. Other RDase accessory genes are colored green. Disruptions of rdhA2 and rdhA7 by an insertion of a transposase gene (tra) and by nonsense mutation, respectively, are indicated. The RDase genes, for which transcription was detected by microarrays are indicated with arrows and substrate names with fold induction. All the substrates indicated above the rdhA2, rdhA3, and rdhA6 genes induced their corresponding gene expression in northern hybridization experiments. 3Cl-4OH-BA; 3-chloro-4-hydroxybenzoate, o-BP; ortho-bromophenol, 3,5-DCP; 3,5-dichlorophenol.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 5: Physical map of the reductive dehalogenase (rdh) operons in D. hafniense DCB-2. The catalytic RDase subunit genes, rdhA1 through rdhA7, are colored black, and the docking protein genes, rdhB1 through rdhB7, are colored yellow. Other RDase accessory genes are colored green. Disruptions of rdhA2 and rdhA7 by an insertion of a transposase gene (tra) and by nonsense mutation, respectively, are indicated. The RDase genes, for which transcription was detected by microarrays are indicated with arrows and substrate names with fold induction. All the substrates indicated above the rdhA2, rdhA3, and rdhA6 genes induced their corresponding gene expression in northern hybridization experiments. 3Cl-4OH-BA; 3-chloro-4-hydroxybenzoate, o-BP; ortho-bromophenol, 3,5-DCP; 3,5-dichlorophenol.
Mentions: Desulfitobacterium and Dehalococcoides constitute most of the dehalorespiring bacteria isolates to date. These bacteria can use halogenated compounds such as chlorophenols and chloroethenes as terminal electron acceptors and acquire energy via anaerobic respiration (dehalorespiration). In this process, the halogenated compounds produce halide atoms. D. hafniense DCB-2 was isolated using 2,4,6-trichlorophenol (2,4,6-TCP) [4] as its electron acceptor, and also reduces 2,4,5-TCP, 2,4-dichlorophenol (2,4-DCP), 2,5-DCP, 3-chloro-4-hydroxyphenylacetate (3Cl-4OH-PA), tetrachlorohydroquinone (TCHQ), 2,3,5,6-tetrachloro-4-methoxyphenol (TCMP), and pentachlorophenol (PCP) [4,5,53-55]. A slight conversion of tetrachloroethene (PCE) to trichloroethene (TCE) was reported by resting cells pregrown with 3Cl-4OH-PA [53]. In the DCB-2 genome, seven RDase genes were identified (Figure 4) versus two in D. hafniense Y51, one of which encodes a PCE RDase (DSY2839, Rdh2 in Figure 1) as it was shown to dechlorinate PCE to cis-1,2-dichloroethene via trichloroethene [8,10]. Among the seven DCB-2 RDase genes, rdhA2 and rdhA7 (Dhaf_0696 and Dhaf_2620) appeared to be non-functional since the genes are interrupted by a transposase gene and nonsense mutation, respectively (Figure 4). BLAST analysis of the five intact genes suggested that four of the genes code for o-chlorophenol RDases (rdhA1, rdhA4, rdhA5, rdhA6) and rdhA3 is highly homologous (66.7% identity in amino acid sequence) to the pce gene of Y51 (DSY2839). The operon harboring rdhA6 contains a complete gene set for reductive dehalogenation and is similar in gene organization (cprTKZEBACD) to the one in D. dehalogenans that is inducible by 3-Cl-4OH-PA [56]. RdhB is an integral membrane protein and acts as a membrane anchor for RDase. RdhC and RdhK belong to the NirI/NosR and CRP-FNR families of transcriptional regulatory proteins. RdhD and RdhE are predicted to be molecular chaperones and RdhT is a homolog to trigger factor folding catalysts. Previously, RDase encoded by rdhA6 of DCB-2 was shown to dechlorinate 3-Cl-4OH-PA [57]. We observed, via northern blot analysis, that this gene was also induced in transcription by other halogenated substrates: 3-chloro-4-hydroxybenzoate (3Cl-4OH-BA) and ortho-bromophenol (o-BP) (summarized in Figure 5). In the same experiment, induction by 3,5-dichlorophenol (3,5-DCP) was observed for rdhA3 which was considered to encode a chloroethene RDase. Our cDNA microarray results, obtained from independently prepared samples, were consistent for the high induction of rdhA6 by 3Cl-4OH-BA (70-fold) and of rdhA3 by 3,5-DCP (32-fold). However, we also observed some inconsistent results between the homology data and the expression data, especially when the level of gene expression was low (e.g. o-BP on rdhA3 and rdhA6 in Figure 5).

Bottom Line: In addition, it contained genes for 53 molybdopterin-binding oxidoreductases, 19 flavoprotein paralogs of the fumarate reductase, and many other FAD/FMN-binding oxidoreductases, proving the cell's versatility in both adaptive and reductive capacities.Together with the ability to form spores, the presence of the CO2-fixing Wood-Ljungdahl pathway and the genes associated with oxygen tolerance add flexibility to the cell's options for survival under stress.D. hafniense DCB-2's genome contains genes consistent with its abilities for dehalogenation, metal reduction, N2 and CO2 fixation, anaerobic respiration, oxygen tolerance, spore formation, and biofilm formation which make this organism a potential candidate for bioremediation at contaminated sites.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Microbial Ecology, Michigan State University, East Lansing, MI, USA. kimsang8@msu.edu

ABSTRACT

Background: The genome of the Gram-positive, metal-reducing, dehalorespiring Desulfitobacterium hafniense DCB-2 was sequenced in order to gain insights into its metabolic capacities, adaptive physiology, and regulatory machineries, and to compare with that of Desulfitobacterium hafniense Y51, the phylogenetically closest strain among the species with a sequenced genome.

Results: The genome of Desulfitobacterium hafniense DCB-2 is composed of a 5,279,134-bp circular chromosome with 5,042 predicted genes. Genome content and parallel physiological studies support the cell's ability to fix N2 and CO2, form spores and biofilms, reduce metals, and use a variety of electron acceptors in respiration, including halogenated organic compounds. The genome contained seven reductive dehalogenase genes and four nitrogenase gene homologs but lacked the Nar respiratory nitrate reductase system. The D. hafniense DCB-2 genome contained genes for 43 RNA polymerase sigma factors including 27 sigma-24 subunits, 59 two-component signal transduction systems, and about 730 transporter proteins. In addition, it contained genes for 53 molybdopterin-binding oxidoreductases, 19 flavoprotein paralogs of the fumarate reductase, and many other FAD/FMN-binding oxidoreductases, proving the cell's versatility in both adaptive and reductive capacities. Together with the ability to form spores, the presence of the CO2-fixing Wood-Ljungdahl pathway and the genes associated with oxygen tolerance add flexibility to the cell's options for survival under stress.

Conclusions: D. hafniense DCB-2's genome contains genes consistent with its abilities for dehalogenation, metal reduction, N2 and CO2 fixation, anaerobic respiration, oxygen tolerance, spore formation, and biofilm formation which make this organism a potential candidate for bioremediation at contaminated sites.

Show MeSH
Related in: MedlinePlus