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Populations Implicated in Anaerobic Reductive Dechlorination of 1,2-Dichloropropane in Highly Enriched Bacterial Communities. Kirsti M. Ritalahti, 2004.1,2-Dichloropropane (1,2-D), a widespread groundwater contaminant, can be reductively dechlorinated to propene by anaerobic bacteria . To shed light on the populations involved in the detoxification process, a comprehensive 16S rRNA gene-based bacterial community analysis of two enrichment cultures derived from geographically distinct locations was performed . Analysis of terminal restriction fragments, amplicons obtained with dechlorinator-specific PCR primers, and enumeration with quantitative real-time PCR as well as screening clone libraries all implied that Dehalococcoides populations were involved in 1,2-D dechlorination in both enrichment cultures . Physiological traits (e.g., dechlorination in the presence of ampicillin and a requirement for hydrogen as the electron donor) supported the involvement of Dehalococcoides populations in the dechlorination process . These findings expand the spectrum of chloroorganic compounds used by Dehalococcoides species as growth-supporting electron acceptors . The combined molecular approach allowed a comparison between different 16S rRNA gene-based approaches for the detection of Dehalococcoides populations . Expression of the Nitroarene Dioxygenase Genes in Comamonas sp . Strain JS765 and Acidovorax sp . Strain JS42 Is Induced by Multiple Aromatic Compounds. Daniel J. Lessner, 2003.This work reports a genetic analysis of the expression of nitrobenzene dioxygenase (NBDO) in Comamonas sp . strain JS765 and 2-nitrotoluene dioxygenase (2NTDO) in Acidovorax sp . strain JS42 . Strains JS765 and JS42 possess identical LysR-type regulatory proteins, NbzR and NtdR, respectively . NbzR/NtdR is homologous to NahR, the positive salicylate-responsive transcriptional activator of the naphthalene degradation genes in Pseudomonas putida G7 . The genes encoding NBDO and 2NTDO in each strain are cotranscribed, and transcription starts at the same site within identical promoter regions for each operon . Results from a lacZ reporter gene fusion demonstrated that expression of NBDO and 2NTDO is induced by multiple aromatic compounds, including an array of nitroaromatic compounds (nitrobenzene, 2-, 3-, and 4-nitrotoluene, 2,4- and 2,6-dinitrotoluene, and aminodinitrotoluenes), as well as salicylate and anthranilate . The nitroaromatic compounds appear to be the actual effector molecules . Analysis of ß-galactosidase and 2NTDO activities with strain JS42 demonstrated that NtdR was required for induction by all of the inducing compounds, high basal-level expression of 2NTDO, and complementation of a JS42 ntdR null mutant . Complementation with the closely related regulators NagR (from Ralstonia sp . strain U2) and NahR restored only induction by the archetype inducers, salicylate or salicylate and anthranilate, respectively, and did not restore the high basal level of expression of 2NTDO . The mechanism of 2NTDO gene regulation in JS42, and presumably that of NBDO gene regulation in JS765, appear similar to that of NahR-regulated genes in Pseudomonas putida G7 . However, NbzR and NtdR appear to have evolved a broader specificity in JS42 and JS765, allowing for recognition of nitroaromatic compounds while retaining the ability to respond to salicylate and anthranilate . NtdR is also the first example of a nitroarene-responsive LysR-type transcriptional activator . Diversion of Electron Flow from Methanogenesis to Crystalline Fe(III) Oxide Reduction in Carbon-Limited Cultures of Wetland Sediment Microorganisms. Eric E. Roden, 2003.Electron flow in acetate-limited cultures of wetland sediment microorganisms was diverted from methane production to Fe(III) reduction in the presence of crystalline Fe(III) oxides at surface area loadings equivalent to that of amorphous Fe(III) oxide . The results indicate that inferences regarding the ability of microbial Fe(III) oxide reduction to compete with other terminal electron-accepting processes in anoxic soils and sediments should be based on estimates of bulk microbially available surface site abundance rather than assumed thermodynamic properties of the dominant oxide phase(s) in the soil or sediment .
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