Unknown,Transcriptomics,Genomics,Proteomics

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Global Gene Expression of Dehalococcoides Within a TCE-Dechlorinating Community Under Conditions of Periodic Substrate Supply

ABSTRACT: A microarray targeting four sequenced strains in the Dehalococcoides (Dhc) genus was used to analyze gene expression in a robust long-term trichloroethene (TCE)-degrading microbial community (designated ANAS) during feeding cycles that involve conditions of periodic substrate supply. The Dhc transcriptome was examined at three time-points throughout a batch feeding cycle: T1 (27 h) when TCE, dichloroethene (DCE), and vinyl chloride (VC) were present; T2 (54 h) when only VC remained; and T3 (13 d) when Dhc had been starved of substrate for nine days. 90% of the Dhc ORFs that were detected in the ANAS DNA were found to be expressed as RNA sometime during the time course, demonstrating extraordinary utilization of the streamlined genome. 97% of these transcripts were differentially expressed during the time course, indicating efficiency of transcription through regulation in Dhc. Most Dhc genes were significantly down-regulated at T3, responding to a lack of substrate as would be expected. The tceA and vcrA genes, which code for proteins with known chlorinated ethene reduction functions, were highly expressed at both T1 and T2, whereas two other putative reductive dehalogenase genes (DET0173 and DET1545) were most highly expressed at T2, likely in response to the presence of VC. Hydrogenases were most highly expressed at T1, reflecting their important role in accumulating electrons used to initiate reductive dechlorination and other biosynthesis pathways. Cobalamin transport genes were preferentially expressed at T2, reflecting an increase in corrinoid transport as chloroethenes were degraded and a decrease in activity of the transport system after dehalogenation was complete. This is the first application of a microarray targeting a known genus, including both core genomes and identified strain-specific genes, applied to improve our understanding of transcriptional dynamics within an undefined microbial community. Replicate samples were independently collected, and simultaneously but individually extracted, fragmented, labeled, and hybridized to arrays. Three DNA samples (one from each of the three replicate cycles) and nine RNA samples (one from each of the three time-points in each of the three replicate cycles) were prepared for microarray analysis.

ORGANISM(S): Dehalococcoides

SUBMITTER: Kimberlee West

PROVIDER: E-GEOD-42635 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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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. 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.

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Global Gene Expression of Dehalococcoides Within a TCE-Dechlorinating Community Under Conditions of Periodic Substrate Supply

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