scholarly journals Cyclohexa-1,5-Diene-1-Carbonyl-Coenzyme A (CoA) Hydratases of Geobacter metallireducens and Syntrophus aciditrophicus: Evidence for a Common Benzoyl-CoA Degradation Pathway in Facultative and Strict Anaerobes

2006 ◽  
Vol 189 (3) ◽  
pp. 1055-1060 ◽  
Author(s):  
Franziska Peters ◽  
Yoshifumi Shinoda ◽  
Michael J. McInerney ◽  
Matthias Boll
Keyword(s):  
Coenzyme A ◽  
Anaerobic Bacteria ◽  
Degradation Pathway ◽  
Ring Cleavage ◽  
Strictly Anaerobic ◽  
Significant Activity ◽  
Geobacter Metallireducens ◽  
Sulfate Reducing ◽  
Coa Reductase ◽  
Syntrophus Aciditrophicus

ABSTRACT In the denitrifying bacterium Thauera aromatica, the central intermediate of anaerobic aromatic metabolism, benzoyl-coenzyme A (CoA), is dearomatized by the ATP-dependent benzoyl-CoA reductase to cyclohexa-1,5-diene-1-carbonyl-CoA (dienoyl-CoA). The dienoyl-CoA is further metabolized by a series of β-oxidation-like reactions of the so-called benzoyl-CoA degradation pathway resulting in ring cleavage. Recently, evidence was obtained that obligately anaerobic bacteria that use aromatic growth substrates do not contain an ATP-dependent benzoyl-CoA reductase. In these bacteria, the reactions involved in dearomatization and cleavage of the aromatic ring have not been shown, so far. In this work, a characteristic enzymatic step of the benzoyl-CoA pathway in obligate anaerobes was demonstrated and characterized. Dienoyl-CoA hydratase activities were determined in extracts of Geobacter metallireducens (iron reducing), Syntrophus aciditrophicus (fermenting), and Desulfococcus multivorans (sulfate reducing) cells grown with benzoate. The benzoate-induced genes putatively coding for the dienoyl-CoA hydratases in the benzoate degraders G. metallireducens and S. aciditrophicus were heterologously expressed and characterized. Both gene products specifically catalyzed the reversible hydration of dienoyl-CoA to 6-hydroxycyclohexenoyl-CoA (Km , 80 and 35 μM; V max, 350 and 550 μmol min−1 mg−1, respectively). Neither enzyme had significant activity with cyclohex-1-ene-1-carbonyl-CoA or crotonyl-CoA. The results suggest that benzoyl-CoA degradation proceeds via dienoyl-CoA and 6-hydroxycyclohexanoyl-CoA in strictly anaerobic bacteria. The steps involved in dienoyl-CoA metabolism appear identical in all nonphotosynthetic anaerobic bacteria, although totally different benzene ring-dearomatizing enzymes are present in facultative and obligate anaerobes.

scholarly journals Decarboxylating and Nondecarboxylating Glutaryl-Coenzyme A Dehydrogenases in the Aromatic Metabolism of Obligately Anaerobic Bacteria

2009 ◽  
Vol 191 (13) ◽  
pp. 4401-4409 ◽  
Author(s):  
Simon Wischgoll ◽  
Martin Taubert ◽  
Franziska Peters ◽  
Nico Jehmlich ◽  
Martin von Bergen ◽  
...  
Keyword(s):  
Coenzyme A ◽  
Anaerobic Bacteria ◽  
Oxidative Decarboxylation ◽  
Kinetic Properties ◽  
Strictly Anaerobic ◽  
Amino Acid Residues ◽  
Geobacter Metallireducens ◽  
Sulfate Reducing ◽  
Reverse Transcription Pcr ◽  
Gene Coding

ABSTRACT In anaerobic bacteria using aromatic growth substrates, glutaryl-coenzyme A (CoA) dehydrogenases (GDHs) are involved in the catabolism of the central intermediate benzoyl-CoA to three acetyl-CoAs and CO2. In this work, we studied GDHs from the strictly anaerobic, aromatic compound-degrading organisms Geobacter metallireducens (GDHGeo) (Fe[III] reducing) and Desulfococcus multivorans (GDHDes) (sulfate reducing). GDHGeo was purified from cells grown on benzoate and after the heterologous expression of the benzoate-induced bamM gene. The gene coding for GDHDes was identified after screening of a cosmid gene library. Reverse transcription-PCR revealed that its expression was induced by benzoate; the product was heterologously expressed and isolated. Both wild-type and recombinant GDHGeo catalyzed the oxidative decarboxylation of glutaryl-CoA to crotonyl-CoA at similar rates. In contrast, recombinant GDHDes catalyzed only the dehydrogenation to glutaconyl-CoA. The latter compound was decarboxylated subsequently to crotonyl-CoA by the addition of membrane extracts from cells grown on benzoate in the presence of 20 mM NaCl. All GDH enzymes were purified as homotetramers of a 43- to 44-kDa subunit and contained 0.6 to 0.7 flavin adenine dinucleotides (FADs)/monomer. The kinetic properties for glutaryl-CoA conversion were as follows: for GDHGeo, the Km was 30 ± 2 μM and the V max was 3.2 ± 0.2 μmol min−1 mg−1, and for GDHDes, the Km was 52 ± 5 μM and the V max was 11 ± 1 μmol min−1 mg−1. GDHDes but not GDHGeo was inhibited by glutaconyl-CoA. Highly conserved amino acid residues that were proposed to be specifically involved in the decarboxylation of the intermediate glutaconyl-CoA were identified in GDHGeo but are missing in GDHDes. The differential use of energy-yielding/energy-demanding enzymatic processes in anaerobic bacteria that degrade aromatic compounds is discussed in view of phylogenetic relationships and constraints of overall energy metabolism.

scholarly journals The 5,6,7,8-Tetrahydro-2-Naphthoyl-Coenzyme A Reductase Reaction in the Anaerobic Degradation of Naphthalene and Identification of Downstream Metabolites

2020 ◽  
Vol 86 (15) ◽  
Author(s):  
Philip Weyrauch ◽  
Isabelle Heker ◽  
Andrey V. Zaytsev ◽  
Christian A. von Hagen ◽  
Meike E. Arnold ◽  
...  
Keyword(s):  
Electron Donor ◽  
Anaerobic Degradation ◽  
Coenzyme A ◽  
Degradation Pathway ◽  
Electron Donors ◽  
Ring Cleavage ◽  
Naphthalene Degradation ◽  
Cell Extracts ◽  
Polycyclic Aromatic ◽  
Coa Reductase

ABSTRACT Anaerobic degradation of polycyclic aromatic hydrocarbons has been investigated mostly with naphthalene as a model compound. Naphthalene degradation by sulfate-reducing bacteria proceeds via carboxylation to 2-naphthoic acid, formation of a coenzyme A thioester, and subsequent reduction to 5,6,7,8-tetrahydro-2-naphthoyl-coenzyme A (THNCoA), which is further reduced to hexahydro-2-naphthoyl-CoA (HHNCoA) by tetrahydronaphthoyl-CoA reductase (THNCoA reductase), an enzyme similar to class I benzoyl-CoA reductases. When analyzing THNCoA reductase assays with crude cell extracts and NADH as electron donor via liquid chromatography-mass spectrometry (LC-MS), scanning for putative metabolites, we found that small amounts of the product of an HHNCoA hydratase were formed in the assays, but the downstream conversion by an NAD+-dependent β-hydroxyacyl-CoA dehydrogenase was prevented by the excess of NADH in those assays. Experiments with alternative electron donors indicated that 2-oxoglutarate can serve as an indirect electron donor for the THNCoA-reducing system via a 2-oxoglutarate:ferredoxin oxidoreductase. With 2-oxoglutarate as electron donor, THNCoA was completely converted and further metabolites resulting from subsequent β-oxidation-like reactions and hydrolytic ring cleavage were detected. These metabolites indicate a downstream pathway with water addition to HHNCoA and ring fission via a hydrolase acting on a β’-hydroxy-β-oxo-decahydro-2-naphthoyl-CoA intermediate. Formation of the downstream intermediate cis-2-carboxycyclohexylacetyl-CoA, which is the substrate for the previously described lower degradation pathway leading to the central metabolism, completes the anaerobic degradation pathway of naphthalene. IMPORTANCE Anaerobic degradation of polycyclic aromatic hydrocarbons is poorly investigated despite its significance in anoxic sediments. Using alternative electron donors for the 5,6,7,8-tetrahydro-2-naphthoyl-CoA reductase reaction, we observed intermediary metabolites of anaerobic naphthalene degradation via in vitro enzyme assays with cell extracts of anaerobic naphthalene degraders. The identified metabolites provide evidence that ring reduction terminates at the stage of hexahydro-2-naphthoyl-CoA and a sequence of β-oxidation-like degradation reactions starts with a hydratase acting on this intermediate. The final product of this reaction sequence was identified as cis-2-carboxycyclohexylacetyl-CoA, a compound for which a further downstream degradation pathway has recently been published (P. Weyrauch, A. V. Zaytsev, S. Stephan, L. Kocks, et al., Environ Microbiol 19:2819–2830, 2017, https://doi.org/10.1111/1462-2920.13806). Our study reveals the first ring-cleaving reaction in the anaerobic naphthalene degradation pathway. It closes the gap between the reduction of the first ring of 2-naphthoyl-CoA by 2-napthoyl-CoA reductase and the lower degradation pathway starting from cis-2-carboxycyclohexylacetyl-CoA, where the second ring cleavage takes place.

scholarly journals Structure and Function of the Unusual Tungsten Enzymes Acetylene Hydratase and Class II Benzoyl-Coenzyme A Reductase

2016 ◽  
Vol 26 (1-3) ◽  
pp. 119-137 ◽  
Author(s):  
Matthias Boll ◽  
Oliver Einsle ◽  
Ulrich Ermler ◽  
Peter M.H. Kroneck ◽  
G. Matthias Ullmann
Keyword(s):  
Alkali Metals ◽  
Coenzyme A ◽  
Anaerobic Bacteria ◽  
Class Ii ◽  
Structure And Function ◽  
Organic Chemical ◽  
Strictly Anaerobic ◽  
Dimethyl Sulfoxide Reductase ◽  
Coa Reductase ◽  
And Function

In biology, tungsten (W) is exclusively found in microbial enzymes bound to a bis<i>-</i>pyranopterin cofactor (bis-WPT). Previously known W enzymes catalyze redox oxo/hydroxyl transfer reactions by directly coordinating their substrates or products to the metal. They comprise the W-containing formate/formylmethanofuran dehydrogenases belonging to the dimethyl sulfoxide reductase (DMSOR) family and the aldehyde:ferredoxin oxidoreductase (AOR) families, which form a separate enzyme family within the Mo/W enzymes. In the last decade, initial insights into the structure and function of two unprecedented W enzymes were obtained: the acetaldehyde forming acetylene hydratase (ACH) belongs to the DMSOR and the class II benzoyl-coenzyme A (CoA) reductase (BCR) to the AOR family. The latter catalyzes the reductive dearomatization of benzoyl-CoA to a cyclic diene. Both are key enzymes in the degradation of acetylene (ACH) or aromatic compounds (BCR) in strictly anaerobic bacteria. They are unusual in either catalyzing a nonredox reaction (ACH) or a redox reaction without coordinating the substrate or product to the metal (BCR). In organic chemical synthesis, analogous reactions require totally nonphysiological conditions depending on Hg<sup>2+</sup> (acetylene hydration) or alkali metals (benzene ring reduction). The structural insights obtained pave the way for biological or biomimetic approaches to basic reactions in organic chemistry.

scholarly journals An Aerobic Hybrid Phthalate Degradation Pathway via Phthaloyl-Coenzyme A in Denitrifying Bacteria

2020 ◽  
Vol 86 (11) ◽  
Author(s):  
Christa Ebenau-Jehle ◽  
Christina I. S. L. Soon ◽  
Jonathan Fuchs ◽  
Robin Geiger ◽  
Matthias Boll
Keyword(s):  
Phthalic Acid ◽  
Coenzyme A ◽  
Anaerobic Bacteria ◽  
Degradation Pathway ◽  
Phthalic Acid Esters ◽  
Content Type ◽  
Facultatively Anaerobic ◽  
Oxygen Sensitive ◽  
Acid Esters ◽  
Facultatively Anaerobic Bacteria

ABSTRACT The degradation of the xenobiotic phthalic acid esters by microorganisms is initiated by the hydrolysis to the respective alcohols and ortho-phthalate (hereafter, phthalate). In aerobic bacteria and fungi, oxygenases are involved in the conversion of phthalate to protocatechuate, the substrate for ring-cleaving dioxygenases. In contrast, anaerobic bacteria activate phthalate to the extremely unstable phthaloyl-coenzyme A (CoA), which is decarboxylated by oxygen-sensitive UbiD-like phthaloyl-CoA decarboxylase (PCD) to the central benzoyl-CoA intermediate. Here, we demonstrate that the facultatively anaerobic, denitrifying Thauera chlorobenzoica 3CB-1 and Aromatoleum evansii KB740 strains use phthalate as a growth substrate under aerobic and denitrifying conditions. In vitro assays with extracts from cells grown aerobically with phthalate demonstrated the succinyl-CoA-dependent activation of phthalate followed by decarboxylation to benzoyl-CoA. In T. chlorobenzoica 3CB-1, we identified PCD as a highly abundant enzyme in both aerobically and anaerobically grown cells, whereas genes for phthalate dioxygenases are missing in the genome. PCD was highly enriched from aerobically grown T. chlorobenzoica cells and was identified as an identical enzyme produced under denitrifying conditions. These results indicate that the initial steps of aerobic phthalate degradation in denitrifying bacteria are accomplished by the anaerobic enzyme inventory, whereas the benzoyl-CoA oxygenase-dependent pathway is used for further conversion to central intermediates. Such a hybrid pathway requires intracellular oxygen homeostasis at concentrations low enough to prevent PCD inactivation but sufficiently high to supply benzoyl-CoA oxygenase with its cosubstrate. IMPORTANCE Phthalic acid esters (PAEs) are industrially produced on a million-ton scale per year and are predominantly used as plasticizers. They are classified as environmentally relevant xenobiotics with a number of adverse health effects, including endocrine-disrupting activity. Biodegradation by microorganisms is considered the most effective process to eliminate PAEs from the environment. It is usually initiated by the hydrolysis of PAEs to alcohols and o-phthalic acid. Degradation of o-phthalic acid fundamentally differs in aerobic and anaerobic microorganisms; aerobic phthalate degradation heavily depends on dioxygenase-dependent reactions, whereas anaerobic degradation employs the oxygen-sensitive key enzyme phthaloyl-CoA decarboxylase. We demonstrate that aerobic phthalate degradation in facultatively anaerobic bacteria proceeds via a previously unknown hybrid degradation pathway involving oxygen-sensitive and oxygen-dependent key enzymes. Such a strategy is essential for facultatively anaerobic bacteria that frequently switch between oxic and anoxic environments.

scholarly journals The bzd Gene Cluster, Coding for Anaerobic Benzoate Catabolism, in Azoarcus sp. Strain CIB

2004 ◽  
Vol 186 (17) ◽  
pp. 5762-5774 ◽  
Author(s):  
María J. López Barragán ◽  
Manuel Carmona ◽  
María T. Zamarro ◽  
Bärbel Thiele ◽  
Matthias Boll ◽  
...  
Keyword(s):  
Degradation Pathway ◽  
Ring Cleavage ◽  
Gene Products ◽  
Physiological Control ◽  
Significant Similarity ◽  
Thauera Aromatica ◽  
Benzoate Degradation ◽  
Coa Ligase ◽  
Transcriptional Units ◽  
Coa Reductase

ABSTRACT We report here that the bzd genes for anaerobic benzoate degradation in Azoarcus sp. strain CIB are organized as two transcriptional units, i.e., a benzoate-inducible catabolic operon, bzdNOPQMSTUVWXYZA, and a gene, bzdR, encoding a putative transcriptional regulator. The last gene of the catabolic operon, bzdA, has been expressed in Escherichia coli and encodes the benzoate-coenzyme A (CoA) ligase that catalyzes the first step in the benzoate degradation pathway. The BzdA enzyme is able to activate a wider range of aromatic compounds than that reported for other previously characterized benzoate-CoA ligases. The reduction of benzoyl-CoA to a nonaromatic cyclic intermediate is carried out by a benzoyl-CoA reductase (bzdNOPQ gene products) detected in Azoarcus sp. strain CIB extracts. The bzdW, bzdX, and bzdY gene products show significant similarity to the hydratase, dehydrogenase, and ring-cleavage hydrolase that act sequentially on the product of the benzoyl-CoA reductase in the benzoate catabolic pathway of Thauera aromatica. Benzoate-CoA ligase assays and transcriptional analyses based on lacZ-reporter fusions revealed that benzoate degradation in Azoarcus sp. strain CIB is subject to carbon catabolite repression by some organic acids, indicating the existence of a physiological control that connects the expression of the bzd genes to the metabolic status of the cell.

scholarly journals Fermentative Cyclohexane Carboxylate Formation in Syntrophus aciditrophicus

2016 ◽  
Vol 26 (1-3) ◽  
pp. 165-179 ◽  
Author(s):  
Matthias Boll ◽  
Johannes W. Kung ◽  
Ulrich Ermler ◽  
Berta M. Martins ◽  
Wolfgang Buckel
Keyword(s):  
Citrate Synthase ◽  
Current Knowledge ◽  
Short Chain Fatty Acids ◽  
Degradation Pathway ◽  
Fermentation Products ◽  
Cyclohexane Carboxylate ◽  
Acyl Coa Dehydrogenases ◽  
Glutamate Synthesis ◽  
Coa Reductase ◽  
Syntrophus Aciditrophicus

Short-chain fatty acids such as acetic, propionic, butyric or lactic acids are typical primary fermentation products in the anaerobic feeding chain. Fifteen years ago, a novel fermentation type was discovered in the obligately anaerobic Deltaproteobacterium <i>Syntrophus aciditrophicus</i>. During fermentative growth with crotonate and/or benzoate, acetate is formed in the oxidative branch and cyclohexane carboxylate in the reductive branch. In both cases cyclohexa-1,5-diene-1-carboxyl-CoA (Ch1,5CoA) is a central intermediate that is either formed by a class II benzoyl-CoA reductase (fermentation of benzoate) or by reverse reactions of the benzoyl-CoA degradation pathway (fermentation of crotonate). Here, we summarize the current knowledge of the enzymology involved in fermentations yielding cyclohexane carboxylate as an excreted product. The characteristic enzymes involved are two acyl-CoA dehydrogenases specifically acting on Ch1,5CoA and cyclohex-1-ene-1-carboxyl-CoA. Both enzymes are also employed during the syntrophic growth of <i>S. aciditrophicus</i> with cyclohexane carboxylate as the carbon source in coculture with a methanogen. An investigation of anabolic pathways in <i>S. aciditrophicus</i> revealed a rather unusual pathway for glutamate synthesis involving a <i>Re</i>-citrate synthase. Future work has to address the unresolved question concerning which components are involved in reoxidation of the NADH formed in the oxidative branch of the unique cyclohexane carboxylate fermentation pathway in <i>S. aciditrophicus</i>.

scholarly journals Purification and Characterization of Active-Site Components of the Putative p-Cresol Methylhydroxylase Membrane Complex from Geobacter metallireducens

2008 ◽  
Vol 190 (19) ◽  
pp. 6493-6500 ◽  
Author(s):  
Jörg Johannes ◽  
Alexander Bluschke ◽  
Nico Jehmlich ◽  
Martin von Bergen ◽  
Matthias Boll
Keyword(s):  
Competitive Inhibition ◽  
Anaerobic Bacteria ◽  
Functional Model ◽  
Visible Spectrum ◽  
Spectrometric Analysis ◽  
Strictly Anaerobic ◽  
Geobacter Metallireducens ◽  
Α Subunit ◽  
Hydroxybenzyl Alcohol

ABSTRACT p-Cresol methylhydroxylases (PCMH) from aerobic and facultatively anaerobic bacteria are soluble, periplasmic flavocytochromes that catalyze the first step in biological p-cresol degradation, the hydroxylation of the substrate with water. Recent results suggested that p-cresol degradation in the strictly anaerobic Geobacter metallireducens involves a tightly membrane-bound PCMH complex. In this work, the soluble components of this complex were purified and characterized. The data obtained suggest a molecular mass of 124 ± 15 kDa and a unique αα′β2 subunit composition, with α and α′ representing isoforms of the flavin adenine dinucleotide (FAD)-containing subunit and β representing a c-type cytochrome. Fluorescence and mass spectrometric analysis suggested that one FAD was covalently linked to Tyr394 of the α subunit. In contrast, the α′ subunit did not contain any FAD cofactor and is therefore considered to be catalytically inactive. The UV/visible spectrum was typical for a flavocytochrome with two heme c cofactors and one FAD cofactor. p-Cresol reduced the FAD but only one of the two heme cofactors. PCMH catalyzed both the hydroxylation of p-cresol to p-hydroxybenzyl alcohol and the subsequent oxidation of the latter to p-hydroxybenzaldehyde in the presence of artificial electron acceptors. The very low Km values (1.7 and 2.7 μM, respectively) suggest that the in vivo function of PCMH is to oxidize both p-cresol and p-hydroxybenzyl alcohol. The latter was a mixed inhibitor of p-cresol oxidation, with inhibition constants of a K ic (competitive inhibition) value of 18 ± 9 μM and a K iu (uncompetitive inhibition) value of 235 ± 20 μM. A putative functional model for an unusual PCMH enzyme is presented.

scholarly journals Structural and Functional Characterization of an Electron Transfer Flavoprotein Involved in Toluene Degradation in Strictly Anaerobic Bacteria

2019 ◽  
Vol 201 (21) ◽  
Author(s):  
Marian Samuel Vogt ◽  
Karola Schühle ◽  
Sebastian Kölzer ◽  
Patrick Peschke ◽  
Nilanjan Pal Chowdhury ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Conformational Changes ◽  
Functional Characterization ◽  
Anaerobic Bacteria ◽  
Biochemical Properties ◽  
Strictly Anaerobic ◽  
Toluene Degradation ◽  
Geobacter Metallireducens ◽  
Content Type ◽  
Facultatively Anaerobic

ABSTRACT (R)-Benzylsuccinate is the characteristic initial intermediate of anaerobic toluene metabolism, which is formed by a radical-type addition of toluene to fumarate. Its further degradation proceeds by activation to the coenzyme A (CoA)-thioester and β-oxidation involving a specific (R)-2-benzylsuccinyl-CoA dehydrogenase (BbsG) affiliated with the family of acyl-CoA dehydrogenases. In this report, we present the biochemical properties of electron transfer flavoproteins (ETFs) from the strictly anaerobic toluene-degrading species Geobacter metallireducens and Desulfobacula toluolica and the facultatively anaerobic bacterium Aromatoleum aromaticum. We determined the X-ray structure of the ETF paralogue involved in toluene metabolism of G. metallireducens, revealing strong overall similarities to previously characterized ETF variants but significantly different structural properties in the hinge regions mediating conformational changes. We also show that all strictly anaerobic toluene degraders utilize one of multiple genome-encoded related ETF paralogues, which constitute a distinct clade of similar sequences in the ETF family, for β-oxidation of benzylsuccinate. In contrast, facultatively anaerobic toluene degraders contain only one ETF species, which is utilized in all β-oxidation pathways. Our phylogenetic analysis of the known sequences of the ETF family suggests that at least 36 different clades can be differentiated, which are defined either by the taxonomic group of the respective host species (e.g., clade P for Proteobacteria) or by functional specialization (e.g., clade T for anaerobic toluene degradation). IMPORTANCE This study documents the involvement of ETF in anaerobic toluene metabolism as the physiological electron acceptor for benzylsuccinyl-CoA dehydrogenase. While toluene-degrading denitrifying proteobacteria use a common ETF species, which is also used for other β-oxidation pathways, obligately anaerobic sulfate- or ferric-iron-reducing bacteria use specialized ETF paralogues for toluene degradation. Based on the structure and sequence conservation of these ETFs, they form a new clade that is only remotely related to the previously characterized members of the ETF family. An exhaustive analysis of the available sequences indicated that the protein family consists of several closely related clades of proven or potential electron-bifurcating ETF species and many deeply branching nonbifurcating clades, which either follow the host phylogeny or are affiliated according to functional criteria.

scholarly journals Re-Citrate Synthase from Clostridium kluyveri Is Phylogenetically Related to Homocitrate Synthase and Isopropylmalate Synthase Rather Than to Si-Citrate Synthase

2007 ◽  
Vol 189 (11) ◽  
pp. 4299-4304 ◽  
Author(s):  
Fuli Li ◽  
Christoph H. Hagemeier ◽  
Henning Seedorf ◽  
Gerhard Gottschalk ◽  
Rudolf K. Thauer
Keyword(s):  
Primary Structure ◽  
Coenzyme A ◽  
Citrate Synthase ◽  
Anaerobic Bacteria ◽  
Strictly Anaerobic ◽  
Acetyl Coenzyme A ◽  
Isopropylmalate Synthase ◽  
Cell Extracts ◽  
Homocitrate Synthase ◽  
Clostridium Kluyveri

ABSTRACT The synthesis of citrate from acetyl-coenzyme A and oxaloacetate is catalyzed in most organisms by a Si-citrate synthase, which is Si-face stereospecific with respect to C-2 of oxaloacetate. However, in Clostridium kluyveri and some other strictly anaerobic bacteria, the reaction is catalyzed by a Re-citrate synthase, whose primary structure has remained elusive. We report here that Re-citrate synthase from C. kluyveri is the product of a gene predicted to encode isopropylmalate synthase. C. kluyveri is also shown to contain a gene for Si-citrate synthase, which explains why cell extracts of the organism always exhibit some Si-citrate synthase activity.

Pilot Plant Study on Microaerobic Self-Granulated Sludge Process (Multi-Stage Reversing Flow Bioreactor: MRB)

1991 ◽  
Vol 23 (4-6) ◽  
pp. 973-980 ◽  
Author(s):  
M. Takahashi ◽  
S. Kyosai
Keyword(s):  
Pilot Plant ◽  
High Performance ◽  
Anaerobic Bacteria ◽  
Domestic Wastewater ◽  
Public Works ◽  
Symbiotic Interaction ◽  
Sulfate Reducing ◽  
Pellet Formation ◽  
Multi Stage ◽  
Domestic Wastewater Treatment

A Multi-stage Reversing flow Bioreactor (MRB) was developed by the Public Works Research Institute in 1986. It utilizes the symbiotic interaction between anaerobic bacteria (sulfate reducing bacteria) and microaerobic bacteria (Beggiatoa=filamentous sulfur oxidizing bacteria) for self-granulated pellet formation. A MRB Pilot plant for domestic wastewater treatment (design capacity was 225 m3/day) was constructed in 1988. After several modifications of the initial design, stable pellet formation and high performance were achieved. This paper describes the results of the pilot plant operation.

Sign in / Sign up

Export Citation Format

Share Document