scholarly journals Formate dependent heterodisulfide reduction in a Methanomicrobiales archaeon

2020 ◽  
Author(s):  
Mohd Farid Abdul Halim ◽  
Leslie A Day ◽  
Kyle C Costa
Keyword(s):  
Electron Donor ◽  
Biochemical Study ◽  
Electron Flow ◽  
Heterodisulfide Reductase ◽  
Anaerobic Digesters ◽  
Genes Encoding ◽  
Treatment Facilities ◽  
Biochemical Approach ◽  
Hydrogenotrophic Methanogens ◽  
Essential Reactions

Hydrogenotrophic methanogens produce CH4 using H2 as an electron donor to reduce CO2. In the absence of H2, many are able to use formate or alcohols as alternate electron donors. Methanogens from the order Methanomicrobiales are capable of growth with H2, but many lack genes encoding hydrogenases that are typically found in other hydrogenotrophic methanogens. In an effort to better understand electron flow in methanogens from the Methanomicrobiales, we undertook a genetic and biochemical study of heterodisulfide reductase (Hdr) in Methanoculleus thermophilus. Hdr catalyzes an essential reaction by coupling the first and last steps of methanogenesis through flavin-based electron bifurcation. Hdr from M. thermophilus co-purified with formate dehydrogenase (Fdh) and only displayed activity when formate was supplied as an electron donor. We found no evidence of an Hdr associated hydrogenase, and H2 could not function as an electron donor, even with Hdr purified from cells grown on H2. We found that cells catalyze a formate hydrogenlyase activity that is likely essential for generating the formate needed for the Hdr reaction. Together, these results highlight the importance of formate as an electron donor for methanogenesis and suggest the ability to use formate is closely integrated into the methanogenic pathway in organisms from the order Methanomicrobiales. Importance Methanogens from the order Methanomicrobiales are thought to prefer H2 as an electron donor for growth. They are ubiquitous in anaerobic environments such as in wastewater treatment facilities, anaerobic digesters, and the rumen where they catalyze the terminal steps in the breakdown of organic matter. However, despite their importance, the metabolism of these organisms remains understudied. Using a genetic and biochemical approach, we show that formate metabolism is closely integrated into methanogenesis in Methanoculleus thermophilus. This is due to a requirement for formate as the electron donor to heterodisulfide reductase (Hdr), an enzyme responsible for catalyzing essential reactions in methanogenesis by linking the initial CO2 fixing step to the exergonic, terminal reaction of the pathway. These results suggest that hydrogen is not necessarily the preferred electron donor for all hydrogenotrophic methanogens and provide insight into the metabolism of methanogens from the order Methanomicrobiales.

scholarly journals Flavin Mononucleotide-Binding Flavoprotein Family in the Domain Archaea

2004 ◽  
Vol 186 (1) ◽  
pp. 90-97 ◽  
Author(s):  
Yan-Huai R. Ding ◽  
James G. Ferry
Keyword(s):  
Electron Donor ◽  
Potential Role ◽  
Electron Flow ◽  
Cell Extract ◽  
Open Reading Frames ◽  
Flavin Mononucleotide ◽  
Native Molecular Mass ◽  
Genes Encoding ◽  
Flavin Mononucleotides ◽  
Reading Frames

ABSTRACT The protein (AfpA, for archaeoflavoprotein) encoded by AF1518 in the genome of Archaeoglobus fulgidus was produced in Escherichia coli and characterized. AfpA was found to be a homodimer with a native molecular mass of 43 kDa and containing two noncovalently bound flavin mononucleotides (FMNs). The cell extract of A. fulgidus catalyzed the CO-dependent reduction of AfpA that was stimulated by the addition of ferredoxin. Ferredoxin was found to be a direct electron donor to purified AfpA, whereas rubredoxin was unable to substitute. Neither NADH nor NADPH was an electron donor. Ferricyanide, 2,6-dichlorophenolindophenol, several quinones, ferric citrate, bovine cytochrome c, and O2 accepted electrons from reduced AfpA, whereas coenzyme F420 did not. The rate of cytochrome c reduction was enhanced in the presence of O2 suggesting that superoxide is a product of the interaction of reduced AfpA with O2. Although AF1518 was previously annotated as encoding a decarboxylase involved in coenzyme A biosynthesis, the results establish that AfpA is an electron carrier protein with ferredoxin as the physiological electron donor. The genomes of several diverse Archaea contained afpA homologs clustered with open reading frames annotated as homologs of genes encoding reductases involved in the oxidative stress response of anaerobes from the domain Bacteria. A potential role for AfpA in coupling electron flow from ferredoxin to the putative reductases is discussed. A search of the databases suggests that AfpA is the prototype of a previously unrecognized flavoprotein family unique to the domain Archaea for which the name archaeoflavoprotein is proposed.

Effect of Magnesium and Calcium Ions on the Photoelectron Transport Activity of Low-Salt Suspended Hydrilla verticillata Thylakoids: Possible Sites of Cation Interaction

1998 ◽  
Vol 53 (9-10) ◽  
pp. 849-856
Author(s):  
Sujata R. Mishra ◽  
Surendra Chandra Sabat
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Electron Donor ◽  
Water Oxidation ◽  
Electron Flow ◽  
Hydrilla Verticillata ◽  
Transport Activity ◽  
Low Salt ◽  
Electron Transport Activity ◽  
Stimulation Of

Stimulatory effect of divalent cations like calcium (Ca2+) and magnesium (Mg2+) was investigated on electron transport activity of divalent cation deficient low-salt suspended (LS) thylakoid preparation from a submerged aquatic angiosperm, Hydrilla verticillata. Both the cations stimulated electron transport activity of LS-suspended thylakoids having an intact water oxidation complex. But in hydroxylamine (NH2OH) - or alkaline Tris - washed thylakoid preparations (with the water oxidation enzyme impaired), only Ca2+ dependent stimulation of electron transport activity was found. The apparent Km of Ca2+ dependent stimulation of electron flow from H2O (endogenous) or from artificial electron donor (exogenous) to dichlorophenol indophenol (acceptor) was found to be identical. Calcium supported stimulation of electron transport activity in NH2OH - or Tris - washed thylakoids was electron donor selective, i.e., Ca2+ ion was only effective in electron flow with diphenylcarbazide but not with NH2OH as electron donor to photosystem II. A magnesium effect was observed in thylakoids having an intact water oxidation complex and the ion became unacceptable in NH2OH - or Tris - washed thylakoids. Indirect experimental evidences have been presented to suggest that Mg2+ interacts with the water oxidation complex, while the Ca2+ interaction is localized betw een Yz and reaction center of photosystem II.

scholarly journals Oxygen reduction in the strict anaerobe Desulfovibrio vulgaris Hildenborough: characterization of two membrane-bound oxygen reductases

Microbiology ◽  
2011 ◽  
Vol 157 (9) ◽  
pp. 2720-2732 ◽  
Author(s):  
O. Lamrabet ◽  
L. Pieulle ◽  
C. Aubert ◽  
F. Mouhamar ◽  
P. Stocker ◽  
...  
Keyword(s):  
Electron Donor ◽  
Desulfovibrio Vulgaris ◽  
Strictly Anaerobic ◽  
Quinol Oxidase ◽  
Genes Encoding ◽  
Oxygen Reductase ◽  
Membrane Bound ◽  
Carbon Monoxide Binding ◽  
Cellular Compartments ◽  
Encoding Genes

Although Desulfovibrio vulgaris Hildenborough (DvH) is a strictly anaerobic bacterium, it is able to consume oxygen in different cellular compartments, including extensive periplasmic O2 reduction with hydrogen as electron donor. The genome of DvH revealed the presence of cydAB and cox genes, encoding a quinol oxidase bd and a cytochrome c oxidase, respectively. In the membranes of DvH, we detected both quinol oxygen reductase [inhibited by heptyl-hydroxyquinoline-N-oxide (HQNO)] and cytochrome c oxidase activities. Spectral and HPLC data for the membrane fraction revealed the presence of o-, b- and d-type haems, in addition to a majority of c-type haems, but no a-type haem, in agreement with carbon monoxide-binding analysis. The cytochrome c oxidase is thus of the cc(o/b)o 3 type, a type not previously described. The monohaem cytochrome c 553 is an electron donor to the cytochrome c oxidase; its encoding gene is located upstream of the cox operon and is 50-fold more transcribed than coxI encoding the cytochrome c oxidase subunit I. Even when DvH is grown under anaerobic conditions in lactate/sulfate medium, the two terminal oxidase-encoding genes are expressed. Furthermore, the quinol oxidase bd-encoding genes are more highly expressed than the cox genes. The cox operon exhibits an atypical genomic organization, with the gene coxII located downstream of coxIV. The occurrence of these membrane-bound oxygen reductases in other strictly anaerobic Deltaproteobacteria is discussed.

Heat-stress stimulation of electron flow in a photosystem I submembrane fraction

1990 ◽  
Vol 68 (7-8) ◽  
pp. 999-1004 ◽  
Author(s):  
Natalie Boucher ◽  
Johanne Harnois ◽  
Robert Carpentier
Keyword(s):  
Heat Stress ◽  
Cytochrome B ◽  
Electron Donor ◽  
Photosystem I ◽  
Conformational Changes ◽  
Electron Flow ◽  
Primary Electron ◽  
Primary Electron Donor ◽  
Terminal Electron Acceptor ◽  
Stimulation Of

Oxygen uptake using methyl viologen as the terminal electron acceptor was recorded in digitonin-derived photosystem I submembrane fractions incubated at either 25 or 50 °C. A two- to four-fold heat-stress stimulation of electron flow was detected at 50 °C when reduced 2,6-dichlorophenol-indophenol was used as the primary electron donor. However, no stimulation was seen with N,N,N′,N′ -tetramethylphenylenediamine as the donor. The stimulation was enhanced by specific cations (Mg2+, Na+, K+), but not by Mn2 or Ca2+. The enhancement obtained with Mg2+ could be eliminated by incubating for a prolonged period. It is proposed that the observed heat-stress stimulation is due to a conformational change at the level of the cytochrome b6–f complex. This change increased the affinity of the protein complex for 2,6-dichlorophenol-indophenol at its oxidation sites. The involvement of a conformational modification is demonstrated by the absence of heat-stress stimulation in submembrane fractions immobilized in an albumin–glutaraldehyde cross-linked matrix.Key words: electron transport, photosystem I, heat stress, cytochrome b6–f complex, conformational changes, electron donor.

scholarly journals Effects of Deletion of Genes Encoding Fe-Only Hydrogenase of Desulfovibrio vulgaris Hildenborough on Hydrogen and Lactate Metabolism

2002 ◽  
Vol 184 (3) ◽  
pp. 679-686 ◽  
Author(s):  
Brant K. J. Pohorelic ◽  
Johanna K. Voordouw ◽  
Elisabeth Lojou ◽  
Alain Dolla ◽  
Jens Harder ◽  
...  
Keyword(s):  
Sulfate Reduction ◽  
Electron Donor ◽  
Type Strain ◽  
Wild Type Strain ◽  
Physiological Role ◽  
Hydrogen Uptake ◽  
Desulfovibrio Vulgaris ◽  
Lactate Metabolism ◽  
Wild Type ◽  
Genes Encoding

ABSTRACT The physiological properties of a hyd mutant of Desulfovibrio vulgaris Hildenborough, lacking periplasmic Fe-only hydrogenase, have been compared with those of the wild-type strain. Fe-only hydrogenase is the main hydrogenase of D. vulgaris Hildenborough, which also has periplasmic NiFe- and NiFeSe-hydrogenases. The hyd mutant grew less well than the wild-type strain in media with sulfate as the electron acceptor and H2 as the sole electron donor, especially at a high sulfate concentration. Although the hyd mutation had little effect on growth with lactate as the electron donor for sulfate reduction when H2 was also present, growth in lactate- and sulfate-containing media lacking H2 was less efficient. The hyd mutant produced, transiently, significant amounts of H2 under these conditions, which were eventually all used for sulfate reduction. The results do not confirm the essential role proposed elsewhere for Fe-only hydrogenase as a hydrogen-producing enzyme in lactate metabolism (W. A. M. van den Berg, W. M. A. M. van Dongen, and C. Veeger, J. Bacteriol. 173:3688–3694, 1991). This role is more likely played by a membrane-bound, cytoplasmic Ech-hydrogenase homolog, which is indicated by the D. vulgaris genome sequence. The physiological role of periplasmic Fe-only hydrogenase is hydrogen uptake, both when hydrogen is and when lactate is the electron donor for sulfate reduction.

scholarly journals Evaluating the impacts of triclosan on wastewater treatment performance during startup and acclimation

2017 ◽  
Vol 77 (2) ◽  
pp. 493-503 ◽  
Author(s):  
R. M. Holzem ◽  
C. M. Gardner ◽  
C. K. Gunsch
Keyword(s):  
Wastewater Treatment ◽  
Community Diversity ◽  
Synthetic Wastewater ◽  
Batch Reactors ◽  
Ammonia Oxidizing Bacteria ◽  
Sequencing Batch Reactors ◽  
Anaerobic Digesters ◽  
Treatment Performance ◽  
Treatment Facilities ◽  
The Impact

Abstract Triclosan (TCS) is a broad range antimicrobial agent used in many personal care products, which is commonly discharged to wastewater treatment facilities (WWTFs). This study examined the impact of TCS on wastewater treatment performance using laboratory bench-scale sequencing batch reactors (SBRs) coupled with anaerobic digesters. The SBRs were continuously fed synthetic wastewater amended with or without 0.68 μM TCS, with the aim of determining the effect of chronic TCS exposure as opposed to a pulse TCS addition as previously studied. Overall, the present study suggests inhibition of nitrogen removal during reactor startup. However, NH4+ removal fully rebounded after 63 days, suggesting acclimation of the associated microbial communities to TCS. An initial decrease in microbial community diversity was observed in the SBRs fed TCS as compared to the control SBRs, followed by an increase in community diversity, which coincided with the increase in NH4+ removal. Elevated levels of NO3− and NO2− were found in the reactor effluent after day 58, however, suggesting ammonia oxidizing bacteria rebounding more rapidly than nitrogen oxidizing bacteria. Similar effects on treatment efficiencies at actual WWTFs have not been widely observed, suggesting that continuous addition of TCS in their influent may have selected for TCS-resistant nitrogen oxidizing bacteria.

scholarly journals Coral symbionts exhibit a polycistronic flavodiiron gene leading to functional proteins in photosynthesis

2021 ◽  
Author(s):  
Ginga Shimakawa ◽  
Eiichi Shoguchi ◽  
Adrien Burlacot ◽  
Kentaro Ifuku ◽  
Yufen Che ◽  
...  
Keyword(s):  
Green Algae ◽  
Electron Flow ◽  
Living Environment ◽  
Land Plants ◽  
Coding Region ◽  
Amino Acid Sequence Alignment ◽  
Genomic Arrangement ◽  
The Family ◽  
Genes Encoding

Photosynthesis in cyanobacteria, green algae, and basal land plants is protected against excess reducing pressure on the photosynthetic chain by flavodiiron proteins (FLV) that dissipate photosynthetic electrons by reducing O2. In these organisms, the genes encoding FLV are always conserved in the form of a pair of two-type isozymes (FLVA and FLVB) that are believed to function in O2 photo-reduction as a heterodimer. While coral symbionts (dinoflagellates of the family Symbiodiniaceae) are the only algae to harbor FLV in photosynthetic red plastid lineage, only one gene is found in transcriptomes and its role and activity remain unknown. Here, we characterized the FLV genes in Symbiodiniaceae and found that its coding region is composed of tandemly repeated FLV sequences. By measuring the O2-dependent electron flow and P700 oxidation, we suggest that this atypical FLV is active in vivo. Based on the amino-acid sequence alignment and the phylogenetic analysis, we conclude that in coral symbionts, the gene pair for FLVA and FLVB have been fused to construct one coding region for a hybrid enzyme, which presumably occurred when or after both genes were inherited from basal green algae to the dinoflagellate. Immunodetection suggested the FLV polypeptide to be cleaved by a post-translational mechanism, adding it to the rare cases of polycistronic genes in eukaryotes. Our results demonstrate that FLV are active in coral symbionts with genomic arrangement that is unique to these species. The implication of these unique features on their symbiotic living environment is discussed.

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