Tetrachloroethene respiration in Sulfurospirillum species is regulated by a two-component system as unraveled by comparative genomics, transcriptomics, and regulator binding studies.

Energy conservation via organohalide respiration (OHR) in dehalogenating Sulfurospirillum species is an inducible process. However, the gene products involved in tetrachloroethene (PCE) sensing and signal transduction have not been unambiguously identified. Here, genome sequencing of Sulfurospirillum strains defective in PCE respiration and comparative genomics, which included the PCE-respiring representatives of the genus, uncovered the genetic inactivation of a two-component system (TCS) in the OHR gene region of the natural mutants. The assumption that the TCS gene products serve as a PCE sensor that initiates gene transcription was supported by the constitutive low-level expression of the TCS operon in fumarate-adapted cells of Sulfurospirillum multivorans. Via RNA sequencing, eight transcriptional units were identified in the OHR gene region, which includes the TCS operon, the PCE reductive dehalogenase operon, the gene cluster for norcobamide biosynthesis, and putative accessory genes with unknown functions. The OmpR-family response regulator (RR) encoded in the TCS operon was functionally characterized by promoter-binding assays. The RR bound a cis-regulatory element that contained a consensus sequence of a direct repeat (CTATW) separated by 17 bp. Its location either overlapping the -35 box or 50 bp further upstream indicated different regulatory mechanisms. Sequence variations in the regulator binding sites identified in the OHR gene region were in accordance with differences in the transcript levels of the respective gene clusters forming the PCE regulon. The results indicate the presence of a fine-tuned regulatory network controlling PCE metabolism in dehalogenating Sulfurospirillum species, a group of metabolically versatile organohalide-respiring bacteria.

Reductive tetrachloroethene dehalogenation in the presence of oxygen by Sulfurospirillum multivorans: physiological studies and proteome analysis.

Reductive dehalogenation of organohalides is carried out by organohalide-respiring bacteria (OHRB) in anoxic environments. The tetrachloroethene (PCE)-respiring Epsilonproteobacterium Sulfurospirillum multivorans is one of few OHRB able to respire oxygen. Therefore, we investigated the organism's capacity to dehalogenate PCE in the presence of oxygen, which would broaden the applicability to use S. multivorans, unlike other commonly oxygen-sensitive OHRB, for bioremediation, e.g. at oxic/anoxic interphases. Additionally, this has an impact on our understanding of the global halogen cycle. Sulfurospirillum multivorans performs dehalogenation of PCE to cis-1,2-dichloroethene at oxygen concentrations below 0.19 mg/L. The redox potential of the medium electrochemically adjusted up to +400 mV had no influence on reductive dehalogenation by S. multivorans in our experiments, suggesting that higher levels of oxygen impair PCE dechlorination by inhibiting or inactivating involved enzymes. The PCE reductive dehalogenase remained active in cell extracts of S. multivorans exposed to 0.37 mg/L oxygen for more than 96 h. Analysis of the proteome revealed that superoxide reductase and cytochrome peroxidase amounts increased with 5% oxygen in the gas phase, while the response to atmospheric oxygen concentrations involved catalase and hydrogen peroxide reductase. Taken together, our results demonstrate that reductive dehalogenation by OHRB is not limited to anoxic conditions.

Proteomic data set of the organohalide-respiring Epsilonproteobacterium Sulfurospirillum multivorans adapted to tetrachloroethene and other energy substrates.

Sulfurospirillum multivorans is a free-living, physiologically versatile Epsilonproteobacterium able to couple the reductive dehalogenation of chlorinated and brominated ethenes to growth (organohalide respiration). We present proteomic data of S. multivorans grown with different electron donors (formate or pyruvate) and electron acceptors (fumarate, nitrate, or tetrachloroethene [PCE]). To obtain information on the cellular localization of proteins, membrane extracts and soluble fractions were separated before data collection from both fractions. The proteome analysis of S. multivorans was performed by mass spectrometry (nanoLC-MS/MS). Raw data have been deposited at ProteomeXchange, "ProteomeXchange provides globally coordinated proteomics data submission and dissemination" [1], via the PRIDE partner repository with the dataset identifier PRIDE: PXD004011. The data might support further research in organohalide respiration and in the general metabolism of free-living Epsilonproteobacteria. The dataset is associated with a previously published study "Proteomics of the organohalide-respiring Epsilonproteobacterium S. multivorans adapted to tetrachloroethene and other energy substrates" [2].

Proteomics of the organohalide-respiring Epsilonproteobacterium Sulfurospirillum multivorans adapted to tetrachloroethene and other energy substrates.

Organohalide respiration is an environmentally important but poorly characterized type of anaerobic respiration. We compared the global proteome of the versatile organohalide-respiring Epsilonproteobacterium Sulfurospirillum multivorans grown with different electron acceptors (fumarate, nitrate, or tetrachloroethene [PCE]). The most significant differences in protein abundance were found for gene products of the organohalide respiration region. This genomic region encodes the corrinoid and FeS cluster containing PCE reductive dehalogenase PceA and other proteins putatively involved in PCE metabolism such as those involved in corrinoid biosynthesis. The latter gene products as well as PceA and a putative quinol dehydrogenase were almost exclusively detected in cells grown with PCE. This finding suggests an electron flow from the electron donor such as formate or pyruvate via the quinone pool and a quinol dehydrogenase to PceA and the terminal electron acceptor PCE. Two putative accessory proteins, an IscU-like protein and a peroxidase-like protein, were detected with PCE only and might be involved in PceA maturation. The proteome of cells grown with pyruvate instead of formate as electron donor indicates a route of electrons from reduced ferredoxin via an Epsilonproteobacterial complex I and the quinone pool to PCE.

Insights into organohalide respiration and the versatile catabolism of Sulfurospirillum multivorans gained from comparative genomics and physiological studies.

Sulfurospirillum multivorans, a free-living ε-proteobacterium, is among the best studied organisms capable of organohalide respiration. It is able to use several halogenated ethenes as terminal electron acceptor. In this report, the complete genome sequence of S. multivorans including a comparison with genome sequences of two related non-dehalogenating species, Sulfurospirillum deleyianum and Sulfurospirillum barnesii, is described. The 3.2 Mbp genome of S. multivorans revealed a ∼ 50 kbp gene region encoding proteins required for organohalide respiration and corrinoid cofactor biosynthesis. This region includes genes for components not detected before in organohalide-respiring organisms. A transcript analysis of genes coding for some of these proteins indicates the involvement of a putative quinol dehydrogenase in organohalide respiration. The presence of genes encoding a variety of oxidoreductases reflects the organism's metabolic versatility. This was confirmed by growth studies with different electron acceptors including perchlorate and several sulfur-containing compounds. A comparison with other ε-proteobacteria indicates horizontal acquisition of many genes in the S. multivorans genome, which might be the basis of the bacterium's catabolic flexibility.