Insights into the Fundamental Physiology of the Uncultured Fe-Oxidizing BacteriumLeptothrix ochracea

ABSTRACTLeptothrix ochraceais known for producing large volumes of iron oxyhydroxide sheaths that alter wetland biogeochemistry. For over a century, these delicate structures have fascinated microbiologists and geoscientists. BecauseL. ochraceastill resists long-termin vitroculture, the debate regarding its metabolic classification dates back to 1885. We developed a novel culturing technique forL. ochraceausingin situnatural waters and coupled this with single-cell genomics and nanoscale secondary-ion mass spectrophotometry (nanoSIMS) to probeL. ochracea's physiology. In microslide culturesL. ochraceadoubled every 5.7 h and had an absolute growth requirement for ferrous iron, the genomic capacity for iron oxidation, and a branched electron transport chain with cytochromes putatively involved in lithotrophic iron oxidation. Additionally, its genome encoded several electron transport chain proteins, including a molybdopterin alternative complex III (ACIII), a cytochromebdoxidase reductase, and several terminal oxidase genes.L. ochraceacontained two key autotrophic proteins in the Calvin-Benson-Bassham cycle, a form II ribulose bisphosphate carboxylase, and a phosphoribulose kinase.L. ochraceaalso assimilated bicarbonate, although calculations suggest that bicarbonate assimilation is a small fraction of its total carbon assimilation. Finally,L. ochracea's fundamental physiology is a hybrid of those of the chemolithotrophicGallionella-type iron-oxidizing bacteria and the sheathed, heterotrophic filamentous metal-oxidizing bacteria of theLeptothrix-Sphaerotilusgenera. This allowsL. ochraceato inhabit a unique niche within the neutrophilic iron seeps.IMPORTANCELeptothrix ochraceawas one of three groups of organisms that Sergei Winogradsky used in the 1880s to develop his hypothesis on chemolithotrophy.L. ochraceacontinues to resist cultivation and appears to have an absolute requirement for organic-rich waters, suggesting that its true physiology remains unknown. Further,L. ochraceais an ecological engineer; a fewL. ochraceacells can generate prodigious volumes of iron oxyhydroxides, changing the ecosystem's geochemistry and ecology. Therefore, to determineL. ochracea's basic physiology, we employed new single-cell techniques to demonstrate thatL. ochraceaoxidizes iron to generate energy and, despite having predicted genes for autotrophic growth, assimilates a fraction of the total CO2that autotrophs do. Although not a true chemolithoautotroph,L. ochracea's physiological strategy allows it to be flexible and to extensively colonize iron-rich wetlands.

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AB0031 T HELPER 17 CELLS WERE SIGNIFICANTLY DECREASED BY MITOCHONDRIAL ELECTRON TRANSPORT CHAIN COMPLEX INHIBITOR IN PATIENTS WITH RHEUMATOID ARTHRITIS

Annals of the Rheumatic Diseases ◽

10.1136/annrheumdis-2020-eular.3441 ◽

2020 ◽

Vol 79 (Suppl 1) ◽

pp. 1318.2-1318

Author(s):

H. R. Lee ◽

S. J. Yoo ◽

J. Kim ◽

I. S. Yoo ◽

C. K. Park ◽

...

Keyword(s):

Rheumatoid Arthritis ◽

Electron Transport ◽

Disease Activity ◽

Th17 Cells ◽

Electron Transport Chain ◽

Chain Complex ◽

Complex Iii ◽

Mitochondrial Electron Transport Chain ◽

Transport Chain ◽

Healthy Control

Background:Reactive oxygen species (ROS) and T helper 17 (TH17) cells have been known to play an important role in the pathogenesis of rheumatoid arthritis (RA). However, the interrelationship between ROS and TH17 remains unclear in RAObjectives:To explore whether ROS affect TH17 cells in peripheral blood mononuclear cells (PBMC) of RA patients, we analyzed ROS expressions among T cell subsets following treatment with mitochondrial electron transport chain complex inhibitors.Methods:Blood samples were collected from 40 RA patients and 10 healthy adult volunteers. RA activity was divided according to clinical parameter DAS28. PBMC cells were obtained from the whole blood using lymphocyte separation medium density gradient centrifugation. Following PBMC was stained with Live/Dead stain dye, cells were incubated with antibodies for CD3, CD4, CD8, and CD25. After fixation and permeabilization, samples were stained with antibodies for FoxP3 and IL-17A. MitoSox were used for mitochondrial specific staining.Results:The frequency of TH17 cells was increased by 4.83 folds in moderate disease activity group (5.1>DAS28≥3.2) of RA patients compared to healthy control. Moderate RA activity patients also showed higher ratio of TH17/Treg than healthy control (3.57 folds). All RA patients had elevated expression of mitochondrial specific ROS than healthy control. When PBMC cells were treated with 2.5uM of antimycin A (mitochondrial electron transport chain complex III inhibitor) for 16 h, the frequency of TH17 cells was significantly decreased.Conclusion:The mitochondrial electron transport chain complex III inhibitor markedly downregulated the frequency of TH17 cells in moderate disease activity patients with RA. These findings provide a novel approach to regulate TH17 function in RA through mitochondrial metabolism related ROS production.References:[1]Szekanecz, Z., et al., New insights in synovial angiogenesis. Joint Bone Spine, 2010. 77(1): p. 13-9.[2]Prevoo, M.L., et al., Modified disease activity scores that include twenty-eight-joint counts. Development and validation in a prospective longitudinal study of patients with rheumatoid arthritis. Arthritis Rheum, 1995. 38(1): p. 44-8.Disclosure of Interests:None declared

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Physiological Evidence for Isopotential Tunneling in the Electron Transport Chain of Methane-Producing Archaea

Applied and Environmental Microbiology ◽

10.1128/aem.00950-17 ◽

2017 ◽

Vol 83 (18) ◽

Cited By ~ 5

Author(s):

Nikolas Duszenko ◽

Nicole R. Buan

Keyword(s):

Escherichia Coli ◽

Electron Transport ◽

Stationary Phase ◽

Exponential Growth ◽

Electron Transport Chain ◽

Methanosarcina Barkeri ◽

Metabolic Efficiency ◽

Methanosarcina Acetivorans ◽

Content Type ◽

Transport Chain

ABSTRACT Many, but not all, organisms use quinones to conserve energy in their electron transport chains. Fermentative bacteria and methane-producing archaea (methanogens) do not produce quinones but have devised other ways to generate ATP. Methanophenazine (MPh) is a unique membrane electron carrier found in Methanosarcina species that plays the same role as quinones in the electron transport chain. To extend the analogy between quinones and MPh, we compared the MPh pool sizes between two well-studied Methanosarcina species, Methanosarcina acetivorans C2A and Methanosarcina barkeri Fusaro, to the quinone pool size in the bacterium Escherichia coli. We found the quantity of MPh per cell increases as cultures transition from exponential growth to stationary phase, and absolute quantities of MPh were 3-fold higher in M. acetivorans than in M. barkeri. The concentration of MPh suggests the cell membrane of M. acetivorans, but not of M. barkeri, is electrically quantized as if it were a single conductive metal sheet and near optimal for rate of electron transport. Similarly, stationary (but not exponentially growing) E. coli cells also have electrically quantized membranes on the basis of quinone content. Consistent with our hypothesis, we demonstrated that the exogenous addition of phenazine increases the growth rate of M. barkeri three times that of M. acetivorans. Our work suggests electron flux through MPh is naturally higher in M. acetivorans than in M. barkeri and that hydrogen cycling is less efficient at conserving energy than scalar proton translocation using MPh. IMPORTANCE Can we grow more from less? The ability to optimize and manipulate metabolic efficiency in cells is the difference between commercially viable and nonviable renewable technologies. Much can be learned from methane-producing archaea (methanogens) which evolved a successful metabolic lifestyle under extreme thermodynamic constraints. Methanogens use highly efficient electron transport systems and supramolecular complexes to optimize electron and carbon flow to control biomass synthesis and the production of methane. Worldwide, methanogens are used to generate renewable methane for heat, electricity, and transportation. Our observations suggest Methanosarcina acetivorans, but not Methanosarcina barkeri, has electrically quantized membranes. Escherichia coli, a model facultative anaerobe, has optimal electron transport at the stationary phase but not during exponential growth. This study also suggests the metabolic efficiency of bacteria and archaea can be improved using exogenously supplied lipophilic electron carriers. The enhancement of methanogen electron transport through methanophenazine has the potential to increase renewable methane production at an industrial scale.

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Vibrio cholerae VciB Mediates Iron Reduction

Journal of Bacteriology ◽

10.1128/jb.00874-16 ◽

2017 ◽

Vol 199 (12) ◽

Cited By ~ 6

Author(s):

Eric D. Peng ◽

Shelley M. Payne

Keyword(s):

Electron Transport ◽

Vibrio Cholerae ◽

Ferrous Iron ◽

Electron Transport Chain ◽

Iron Reduction ◽

Iron Transport ◽

Ferric Iron ◽

Transport Systems ◽

Content Type ◽

Transport Chain

ABSTRACT Vibrio cholerae is the causative agent of the severe diarrheal disease cholera. V. cholerae thrives within the human host, where it replicates to high numbers, but it also persists within the aquatic environments of ocean and brackish water. To survive within these nutritionally diverse environments, V. cholerae must encode the necessary tools to acquire the essential nutrient iron in all forms it may encounter. A prior study of systems involved in iron transport in V. cholerae revealed the existence of vciB, which, while unable to directly transport iron, stimulates the transport of iron through ferrous (Fe2+) iron transport systems. We demonstrate here a role for VciB in V. cholerae in which VciB stimulates the reduction of Fe3+ to Fe2+, which can be subsequently transported into the cell with the ferrous iron transporter Feo. Iron reduction is independent of functional iron transport but is associated with the electron transport chain. Comparative analysis of VciB orthologs suggests a similar role for other proteins in the VciB family. Our data indicate that VciB is a dimer located in the inner membrane with three transmembrane segments and a large periplasmic loop. Directed mutagenesis of the protein reveals two highly conserved histidine residues required for function. Taken together, our results support a model whereby VciB reduces ferric iron using energy from the electron transport chain. IMPORTANCE Vibrio cholerae is a prolific human pathogen and environmental organism. The acquisition of essential nutrients such as iron is critical for replication, and V. cholerae encodes a number of mechanisms to use iron from diverse environments. Here, we describe the V. cholerae protein VciB that increases the reduction of oxidized ferric iron (Fe3+) to the ferrous form (Fe2+), thus promoting iron acquisition through ferrous iron transporters. Analysis of VciB orthologs in Burkholderia and Aeromonas spp. suggest that they have a similar activity, allowing a functional assignment for this previously uncharacterized protein family. This study builds upon our understanding of proteins known to mediate iron reduction in bacteria.

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A Chemogenomic Screen in Saccharomyces cerevisiae Uncovers a Primary Role for the Mitochondria in Farnesol Toxicity and Its Regulation by the Pkc1 Pathway

Journal of Biological Chemistry ◽

10.1074/jbc.m610575200 ◽

2006 ◽

Vol 282 (7) ◽

pp. 4868-4874 ◽

Cited By ~ 44

Author(s):

Gregory D. Fairn ◽

Kendra MacDonald ◽

Christopher R. McMaster

Keyword(s):

Saccharomyces Cerevisiae ◽

Reactive Oxygen Species ◽

Cell Death ◽

Electron Transport ◽

Signaling Pathway ◽

Electron Transport Chain ◽

Reactive Oxygen ◽

Complex Iii ◽

Oxygen Species ◽

Transport Chain

The isoprenoid farnesol has been shown to preferentially induce apoptosis in cancerous cells; however, the mode of action of farnesol-induced death is not established. We used chemogenomic profiling using Saccharomyces cerevisiae to probe the core cellular processes targeted by farnesol. This screen revealed 48 genes whose inactivation increased sensitivity to farnesol. The gene set indicated a role for the generation of oxygen radicals by the Rieske iron-sulfur component of complex III of the electron transport chain as a major mediator of farnesol-induced cell death. Consistent with this, loss of mitochondrial DNA, which abolishes electron transport, resulted in robust resistance to farnesol. A genomic interaction map predicted interconnectedness between the Pkc1 signaling pathway and farnesol sensitivity via regulation of the generation of reactive oxygen species. Consistent with this prediction (i) Pkc1, Bck1, and Mkk1 relocalized to the mitochondria upon farnesol addition, (ii) inactivation of the only non-essential and non-redundant member of the Pkc1 signaling pathway, BCK1, resulted in farnesol sensitivity, and (iii) expression of activated alleles of PKC1, BCK1, and MKK1 increased resistance to farnesol and hydrogen peroxide. Sensitivity to farnesol was not affected by the presence of the osmostabilizer sorbitol nor did farnesol affect phosphorylation of the ultimate Pkc1-responsive kinase responsible for controlling the cell wall integrity pathway, Slt2. The data indicate that the generation of reactive oxygen species by the electron transport chain is a primary mechanism by which farnesol kills cells. The Pkc1 signaling pathway regulates farnesol-mediated cell death through management of the generation of reactive oxygen species.

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Activity of complex III of the mitochondrial electron transport chain is essential for early heart muscle cell differentiation

The FASEB Journal ◽

10.1096/fj.03-0520fje ◽

2004 ◽

Vol 18 (11) ◽

pp. 1300-1302 ◽

Cited By ~ 56

Author(s):

Dimitry Spitkovsky ◽

Philipp Sasse ◽

Eugen Kolossov ◽

Cornelia Böttinger ◽

Bernd K. Fleischmann ◽

...

Keyword(s):

Cell Differentiation ◽

Electron Transport ◽

Muscle Cell ◽

Heart Muscle ◽

Electron Transport Chain ◽

Complex Iii ◽

Mitochondrial Electron Transport Chain ◽

Heart Muscle Cell ◽

Muscle Cell Differentiation ◽

Transport Chain

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Differential remodeling of the electron transport chain is required to support TLR3 and TLR4 signaling and cytokine production in macrophages

10.1101/742098 ◽

2019 ◽

Author(s):

Duale Ahmed ◽

David Roy ◽

Allison Jaworski ◽

Alex Edwards ◽

Alfonso Abizaid ◽

...

Keyword(s):

Electron Transport ◽

Immune Responses ◽

Electron Transport Chain ◽

Cytokine Production ◽

Critical Role ◽

Innate Immune ◽

Fine Tuning ◽

Complex Iii ◽

Innate Immune Responses ◽

Transport Chain

AbstractIncreasing evidence suggests that mitochondria play a critical role in driving innate immune responses against bacteria and viruses. However, it is unclear if differential reprogramming of mitochondrial function contributes to the fine tuning of pathogen specific immune responses. Here, we found that TLR3 and TLR4 engagement on murine bone marrow derived macrophages was associated with differential remodeling of electron transport chain complex expression. This remodeling was associated with differential accumulation of mitochondrial and cytosolic ROS, which were required to support ligand specific inflammatory and antiviral cytokine production. We also found that the magnitude of TLR3, but not TLR4, responses were modulated by glucose availability. Under conditions of low glucose conditions, TLR3 engagement was associated with increased ETC complex III expression, increased mitochondrial and cytosolic ROS and increased inflammatory and antiviral cytokine production. This amplification was selectively reversed by targeting superoxide production from the outer Q-binding site of the ETC complex III. These results suggest that ligand specific modulation of the ETC may act as a rheostat that fine-tunes innate immune responses via mitochondrial ROS production. Modulation of these processes may represent a novel mechanism to modulate the nature as well as the magnitude of antiviral versus inflammatory immune responses.

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Differential remodeling of the electron transport chain is required to support TLR3 and TLR4 signaling and cytokine production in macrophages

Scientific Reports ◽

10.1038/s41598-019-55295-4 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 3

Author(s):

Duale Ahmed ◽

David Roy ◽

Allison Jaworski ◽

Alexander Edwards ◽

Alfonso Abizaid ◽

...

Keyword(s):

Electron Transport ◽

Immune Responses ◽

Electron Transport Chain ◽

Cytokine Production ◽

Critical Role ◽

Innate Immune ◽

Fine Tuning ◽

Complex Iii ◽

Innate Immune Responses ◽

Transport Chain

AbstractIncreasing evidence suggests that mitochondria play a critical role in driving innate immune responses against bacteria and viruses. However, it is unclear if differential reprogramming of mitochondrial function contributes to the fine tuning of pathogen specific immune responses. Here, we found that TLR3 and TLR4 engagement on murine bone marrow derived macrophages was associated with differential remodeling of electron transport chain complex expression. This remodeling was associated with differential accumulation of mitochondrial and cytosolic ROS, which were required to support ligand specific inflammatory and antiviral cytokine production. We also found that the magnitude of TLR3, but not TLR4, responses were modulated by glucose availability. Under conditions of low glucose, TLR3 engagement was associated with increased ETC complex III expression, increased mitochondrial and cytosolic ROS and increased inflammatory and antiviral cytokine production. This amplification was selectively reversed by targeting superoxide production from the outer Q-binding site of the ETC complex III. These results suggest that ligand specific modulation of the ETC may act as a rheostat that fine tunes innate immune responses via mitochondrial ROS production. Modulation of these processes may represent a novel mechanism to modulate the nature as well as the magnitude of antiviral vs. inflammatory immune responses.

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The efficiency and plasticity of mitochondrial energy transduction

Biochemical Society Transactions ◽

10.1042/bst0330897 ◽

2005 ◽

Vol 33 (5) ◽

pp. 897-904 ◽

Cited By ~ 164

Author(s):

M.D. Brand

Keyword(s):

Electron Transport ◽

Atp Synthase ◽

Electron Transport Chain ◽

Uncoupling Protein ◽

Coupling Efficiency ◽

Energy Transduction ◽

Proton Pumping ◽

Complex Iii ◽

Proton Pumps ◽

Transport Chain

Since it was first realized that biological energy transduction involves oxygen and ATP, opinions about the amount of ATP made per oxygen consumed have continually evolved. The coupling efficiency is crucial because it constrains mechanistic models of the electron-transport chain and ATP synthase, and underpins the physiology and ecology of how organisms prosper in a thermodynamically hostile environment. Mechanistically, we have a good model of proton pumping by complex III of the electron-transport chain and a reasonable understanding of complex IV and the ATP synthase, but remain ignorant about complex I. Energy transduction is plastic: coupling efficiency can vary. Whether this occurs physiologically by molecular slipping in the proton pumps remains controversial. However, the membrane clearly leaks protons, decreasing the energy funnelled into ATP synthesis. Up to 20% of the basal metabolic rate may be used to drive this basal leak. In addition, UCP1 (uncoupling protein 1) is used in specialized tissues to uncouple oxidative phosphorylation, causing adaptive thermogenesis. Other UCPs can also uncouple, but are tightly regulated; they may function to decrease coupling efficiency and so attenuate mitochondrial radical production. UCPs may also integrate inputs from different fuels in pancreatic β-cells and modulate insulin secretion. They are exciting potential targets for treatment of obesity, cachexia, aging and diabetes.

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Ischemic defects in the electron transport chain increase the production of reactive oxygen species from isolated rat heart mitochondria

AJP Cell Physiology ◽

10.1152/ajpcell.00211.2007 ◽

2008 ◽

Vol 294 (2) ◽

pp. C460-C466 ◽

Cited By ~ 199

Author(s):

Qun Chen ◽

Shadi Moghaddas ◽

Charles L. Hoppel ◽

Edward J. Lesnefsky

Keyword(s):

Electron Transport ◽

Complex I ◽

Electron Transport Chain ◽

Myocardial Injury ◽

Complex Iii ◽

Ischemic Damage ◽

Ros Production ◽

Oxygen Species ◽

Net Production ◽

Transport Chain

Cardiac ischemia decreases complex III activity, cytochrome c content, and respiration through cytochrome oxidase in subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). The reversible blockade of electron transport with amobarbital during ischemia protects mitochondrial respiration and decreases myocardial injury during reperfusion. These findings support that mitochondrial damage occurs during ischemia and contributes to myocardial injury during reperfusion. The current study addressed whether ischemic damage to the electron transport chain (ETC) increased the net production of reactive oxygen species (ROS) from mitochondria. SSM and IFM were isolated from 6-mo-old Fisher 344 rat hearts following 25 min global ischemia or following 40 min of perfusion alone as controls. H2O2release from SSM and IFM was measured using the amplex red assay. With glutamate as a complex I substrate, the net production of H2O2was increased by 178 ± 14% and 179 ± 17% in SSM and IFM ( n = 9), respectively, following ischemia compared with controls ( n = 8). With succinate as substrate in the presence of rotenone, H2O2increased by 272 ± 22% and 171 ± 21% in SSM and IFM, respectively, after ischemia. Inhibitors of electron transport were used to assess maximal ROS production. Inhibition of complex I with rotenone increased H2O2production by 179 ± 24% and 155 ± 14% in SSM and IFM, respectively, following ischemia. Ischemia also increased the antimycin A-stimulated production of H2O2from complex III. Thus ischemic damage to the ETC increased both the capacity and the net production of H2O2from complex I and complex III and sets the stage for an increase in ROS production during reperfusion as a mechanism of cardiac injury.

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Hypoxia sensing in the fetal chicken femoral artery is mediated by the mitochondrial electron transport chain

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00500.2009 ◽

2010 ◽

Vol 298 (4) ◽

pp. R1026-R1034 ◽

Cited By ~ 14

Author(s):

Bea Zoer ◽

Angel L. Cogolludo ◽

Francisco Perez-Vizcaino ◽

Jo G. R. De Mey ◽

Carlos E. Blanco ◽

...

Keyword(s):

Polyethylene Glycol ◽

Electron Transport ◽

Electron Transport Chain ◽

Critical Role ◽

Complex Iii ◽

Mitochondrial Electron Transport Chain ◽

Voltage Gated ◽

Femoral Arteries ◽

Transport Chain ◽

Systemic Arteries

Vascular hypoxia sensing is transduced into vasoconstriction in the pulmonary circulation, whereas systemic arteries dilate. Mitochondrial electron transport chain (mETC), reactive O2 species (ROS), and K+ channels have been implicated in the sensing/signaling mechanisms of hypoxic relaxation in mammalian systemic arteries. We aimed to investigate their putative roles in hypoxia-induced relaxation in fetal chicken (19 days of incubation) femoral arteries mounted in a wire myograph. Acute hypoxia (Po2 ∼2.5 kPa) relaxed the contraction induced by norepinephrine (1 μM). Hypoxia-induced relaxation was abolished or significantly reduced by the mETC inhibitors rotenone (complex I), myxothiazol and antimycin A (complex III), and NaN3 (complex IV). The complex II inhibitor 3-nitroproprionic acid enhanced the hypoxic relaxation. In contrast, the relaxations mediated by acetylcholine, sodium nitroprusside, or forskolin were not affected by the mETC blockers. Hypoxia induced a slight increase in ROS production (as measured by 2,7-dichlorofluorescein-fluorescence), but hypoxia-induced relaxation was not affected by scavenging of superoxide (polyethylene glycol-superoxide dismutase) or H2O2 (polyethylene glycol-catalase) or by NADPH-oxidase inhibition (apocynin). Also, the K+ channel inhibitors tetraethylammonium (nonselective), diphenyl phosphine oxide-1 (voltage-gated K+ channel 1.5), glibenclamide (ATP-sensitive K+ channel), iberiotoxin (large-conductance Ca2+-activated K+ channel), and BaCl2 (inward-rectifying K+ channel), as well as ouabain (Na+-K+-ATPase inhibitor) did not affect hypoxia-induced relaxation. The relaxation was enhanced in the presence of the voltage-gated K+ channel blocker 4-aminopyridine. In conclusion, our experiments suggest that the mETC plays a critical role in O2 sensing in fetal chicken femoral arteries. In contrast, hypoxia-induced relaxation appears not to be mediated by ROS or K+ channels.

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