Project description:Tetrachloroethene (PCE) and trichloroethene (TCE) are prevalent groundwater contaminants that can be completely reductively dehalogenated by Dehalococcoides organisms. A Dehalococcoides-containing microbial consortium (ANAS) with the ability to degrade TCE to ethene, an innocuous end-product, was previously enriched from contaminated soil. A whole-genome photolithographic microarray was developed based on the genome of Dehalococcoides ethenogenes 195 (strain 195). This microarray contains probes designed to hybridize to >99% of the predicted protein-coding sequences in the strain 195 genome. DNA from ANAS was hybridized to the microarray to characterize the genomic content of the ANAS enrichment. The microarray revealed that the genes associated with central metabolism including an apparently incomplete carbon fixation pathway, cobalamin salvaging system, nitrogen fixation pathway, and five hydrogenase complexes are present in both strain 195 and ANAS. Although the gene encoding the TCE reductase tceA was detected, 13 of the 19 reductive dehalogenase genes present in strain 195 were not detected in ANAS. Additionally, 88% of the genes in predicted integrated genetic elements in strain 195 were not detected in ANAS, consistent with these elements being genetically mobile. Sections of the tryptophan operon and an operon encoding an ABC transporter in strain 195 were also not detected in ANAS. These insights into the diversity of Dehalococcoides genomes will improve our understanding of the physiology and evolution of these bacteria which is essential in developing effective strategies for bioremediation of PCE and TCE in the environment. Keywords: comparative genomic hybridization Genomic DNA from each culture was divided into replicate samples which were independently fragmented, labeled, and hybridized to arrays. Two microarrays were processed for the positive control (strain 195), two for the negative control (D. restrictus), and five for the ANAS enrichment culture(two analyses from one biological sample followed one year later by three analyses of a second biological sample).

Project description:The chlorinated ethene-respiring bacteria of the genus Dehalococcoides are important for bioremediation. A microarray targeting genes from all available sequenced genomes of the Dehalococcoides genus was designed with 4305 probe sets to target 98.6% of all genes from strains 195, CBDB1, BAV1, and VS. The microarrays were validated with genomic DNA (gDNA) of strains 195 and BAV1 and satisfactory analytical reproducibility, quantitative response and gene detection accuracy were obtained. These microarrays were applied to query the genomes of two recently isolated Dehalococcoides strains, ANAS1 and ANAS2. Strains ANAS1 and ANAS2 can both couple the reduction of TCE, cDCE and 1,1-DCE but not PCE and tDCE with growth while only strain ANAS2 couples VC reduction to growth. Analysis of the respective gDNA using the microarrays showed that the genomes of both strains are similar to each other and to strain 195, except for genes that are within the previously defined integrated elements (IEs) or high plasticity regions (HPRs). Similar results to the combined isolates were obtained when gDNA of ANAS, the enrichment culture from which the two Dehalococcoides isolates originated, was applied to the microarrays. The genome similarities, together with the distinct chlorinated ethene usage of strains ANAS1, ANAS2 and 195 demonstrate that closely phylogenetically related strains can be physiologically different. This incongruence between physiology and core genome phylogeny appears to be driven by the presence of distinct reductive dehalogenase (RDase)-encoding genes with characterized chlorinated ethene functions (pceA, tceA in strain 195; tceA in strain ANAS1; vcrA in strain ANAS2). Genes encoding central metabolic functions of strain 195 were all detected in strains ANAS1 and ANAS2, while interestingly, the tryptophan operon of these strains is similar to that of strain VS. Overall, the microarrays are a valuable high-throughput tool for comparative genomics of un-sequenced Dehalococcoides-containing samples.

Project description:Bacteria of the genus Dehalococcoides play an important role in the reductive dechlorination of chlorinated ethenes. A systems level approach was taken in this study to examine the global transcriptomic and proteomic responses of exponentially growing D. ethenogenes strain 195 to fixed nitrogen limitation (FNL). As expected, the nitrogen-fixing (nif) genes were differentially up-regulated in the transcriptome and proteome of strain 195 during FNL. Aside from the nif operon, a putative methylglyoxal synthase-encoding gene (DET1576), which is predicted to catalyze the formation of the toxic electrophile methylglyoxal and implicated in the uncoupling of anabolism from catabolism in bacteria, was strongly up-regulated in the transcriptome and could potentially play a role in the observed growth inhibition during FNL. Carbon catabolism genes were generally down regulated in response to FNL and a number of transporters were differentially regulated in response to nitrogen limitation, with some playing apparent roles in nitrogen acquisition while others were associated with general stress responses. A number of genes related to the biological functions of nucleotide synthesis, replication, transcription, translation, and post-translational modifications were also differentially expressed. One gene coding for a putative reductive dehalogenase (DET1545) and a number coding for oxidoreductases, which have implications in energy generation and redox reactions, were also differentially regulated. Interestingly, most of the genes within the multiple integrated elements were not differentially expressed. Overall, this study elucidates the molecular responses of strain 195 to FNL and identifies differentially expressed genes that are potential biomarkers to evaluate cellular nitrogen status in the environment. Dehalococcoides ethenogenes strain 195 was grown with or without ammonium in batch cultures with trichloroethene as the electron acceptor, acetate as the carbon source, and hydrogen as the electron donor. Microarrays were used to compare the transcriptome during fixed nitrogen limitation and triplicate biological samples were prepared for each condition. Differentially expressed genes between the two growth conditions were identified using a two-tailed Student's t-test, a false discovery rate of less than 1%, an absolute hybridization signal intensity of 300 or greater in one of the two conditions, and an expression ratio of two-fold or greater.

Project description:The chlorinated ethene-respiring bacteria of the genus Dehalococcoides are important for bioremediation. A microarray targeting genes from all available sequenced genomes of the Dehalococcoides genus was designed with 4305 probe sets to target 98.6% of all genes from strains 195, CBDB1, BAV1, and VS. The microarrays were validated with genomic DNA (gDNA) of strains 195 and BAV1 and satisfactory analytical reproducibility, quantitative response and gene detection accuracy were obtained. These microarrays were applied to query the genomes of two recently isolated Dehalococcoides strains, ANAS1 and ANAS2. Strains ANAS1 and ANAS2 can both couple the reduction of TCE, cDCE and 1,1-DCE but not PCE and tDCE with growth while only strain ANAS2 couples VC reduction to growth. Analysis of the respective gDNA using the microarrays showed that the genomes of both strains are similar to each other and to strain 195, except for genes that are within the previously defined integrated elements (IEs) or high plasticity regions (HPRs). Similar results to the combined isolates were obtained when gDNA of ANAS, the enrichment culture from which the two Dehalococcoides isolates originated, was applied to the microarrays. The genome similarities, together with the distinct chlorinated ethene usage of strains ANAS1, ANAS2 and 195 demonstrate that closely phylogenetically related strains can be physiologically different. This incongruence between physiology and core genome phylogeny appears to be driven by the presence of distinct reductive dehalogenase (RDase)-encoding genes with characterized chlorinated ethene functions (pceA, tceA in strain 195; tceA in strain ANAS1; vcrA in strain ANAS2). Genes encoding central metabolic functions of strain 195 were all detected in strains ANAS1 and ANAS2, while interestingly, the tryptophan operon of these strains is similar to that of strain VS. Overall, the microarrays are a valuable high-throughput tool for comparative genomics of un-sequenced Dehalococcoides-containing samples. The genomic DNA (gDNA) of each culture was analyzed in triplicate. gDNA from strain 195 and strain BAV1 was used as positive control, while gDNA from Anaeromyxobacter dehalogenans strain 2CP-C served as negative control in validating the microarray. gDNA from the two newly isolated strains ANAS1 and ANAS2 as well as the enrichment culture (ANAS) where the two strains originated was also analyzed.

Dataset Information

Comparative Genomics of D. ethenogenes 195 and an Unsequenced Dehalococcoides-Containing Enrichment Culture

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