scholarly journals Energy conservation under extreme energy limitation: the role of cytochromes and quinones in acetogenic bacteria

Extremophiles ◽  
2021 ◽  
Author(s):  
Florian P. Rosenbaum ◽  
Volker Müller
Keyword(s):  
Carbon Dioxide ◽  
Electron Transport ◽  
Metabolic Pathway ◽  
Enzyme Complex ◽  
Acetogenic Bacteria ◽  
Electron Transport Chains ◽  
Energy Limitation ◽  
Respiratory Chains

AbstractAcetogenic bacteria are a polyphyletic group of organisms that fix carbon dioxide under anaerobic, non-phototrophic conditions by reduction of two mol of CO2 to acetyl-CoA via the Wood–Ljungdahl pathway. This pathway also allows for lithotrophic growth with H2 as electron donor and this pathway is considered to be one of the oldest, if not the oldest metabolic pathway on Earth for CO2 reduction, since it is coupled to the synthesis of ATP. How ATP is synthesized has been an enigma for decades, but in the last decade two ferredoxin-dependent respiratory chains were discovered. Those respiratory chains comprise of a cytochrome-free, ferredoxin-dependent respiratory enzyme complex, which is either the Rnf or Ech complex. However, it was discovered already 50 years ago that some acetogens contain cytochromes and quinones, but their role had only a shadowy existence. Here, we review the literature on the characterization of cytochromes and quinones in acetogens and present a hypothesis that they may function in electron transport chains in addition to Rnf and Ech.

The Perennial Riddle of Life’s Origin

2021 ◽  
pp. 82-96
Author(s):  
Franklin M. Harold
Keyword(s):  
Natural Selection ◽  
Electron Transport ◽  
Atp Synthase ◽  
Hydrothermal Vents ◽  
Rna World ◽  
Good Reason ◽  
Dynamic Network ◽  
Electron Transport Chains ◽  
The Origin Of Life

The origin of life is the most consequential problem in biology, possibly in all of science, and it remains unsolved. This chapter summarizes what has been learned and highlights questions that remain open, including How, Where, When, and especially Why. LUCA, some four billion years ago, already featured the basic capacities of contemporary cells. These must have evolved still earlier, at a nebulous proto-cellular stage. There is good reason to believe that enzymes, DNA, ribosomes, electron-transport chains, and the rotary ATP synthase all predate LUCA and were shaped by the standard process of variation and natural selection, but we know next to nothing about how cells ever got started. I favor the proposal that it began with a purely chemical dynamic network capable of reproducing itself, that may have originated by chance. Natural selection would have favored the incorporation of any ancillary factors that promoted its kinetic stability, especially ones that improved reproduction or gave access to energy. All the specifics are in dispute, including the role of a prebiotic broth of organic chemicals, the nature and origin of enclosure, the RNA world, and a venue in submarine hydrothermal vents. My sense is that critical pieces of the puzzle remain to be discovered.

scholarly journals Carbon dioxide binding at a Ni/Fe center: synthesis and characterization of Ni(η1-CO2-κC) and Ni-μ-CO2-κC:κ2O,O′-Fe

2017 ◽  
Vol 8 (1) ◽  
pp. 600-605 ◽  
Author(s):  
Changho Yoo ◽  
Yunho Lee
Keyword(s):  
Carbon Dioxide ◽  
Active Site ◽  
Synthesis And Characterization ◽  
Fe Species

A heterobimetallic Ni-μ-CO2-κC:κ2O,O′-Fe species reminiscent of the CODH active site was synthesized, helping to elucidate the role of the unique iron.

scholarly journals Genetic evidence reveals the indispensable role of the rseC gene for autotrophy and the importance of a functional electron balance for nitrate reduction in Clostridium ljungdahlii

2021 ◽  
Author(s):  
Christian-Marco Klask ◽  
Benedikt Jäger ◽  
Largus T Angenent ◽  
Bastian Molitor
Keyword(s):  
Nitrate Reductase ◽  
Gene Cluster ◽  
Nitrate Reduction ◽  
Transcriptional Repression ◽  
Cellular Growth ◽  
Deletion Strain ◽  
Clostridium Ljungdahlii ◽  
Acetogenic Bacteria ◽  
Energy Limitation

For Clostridium ljungdahlii, the RNF complex plays a key role for energy conversion from gaseous substrates such as hydrogen and carbon dioxide. In a previous study, a disruption of RNF-complex genes led to the loss of autotrophy, while heterotrophy was still possible via glycolysis. Furthermore, it was shown that the energy limitation during autotrophy could be lifted by nitrate supplementation, which resulted in an elevated cellular growth and ATP yield. Here, we used CRISPR-Cas12a to delete: 1) the RNF complex-encoding gene cluster rnfCDGEAB; 2) the putative RNF regulator gene rseC; and 3) a gene cluster that encodes for a putative nitrate reductase. The deletion of either rnfCDGEAB or rseC resulted in a complete loss of autotrophy, which could be restored by plasmid-based complementation of the deleted genes. We observed a transcriptional repression of the RNF-gene cluster in the rseC-deletion strain during autotrophy and investigated the distribution of the rseC gene among acetogenic bacteria. To examine nitrate reduction and its connection to the RNF complex, we compared autotrophic and heterotrophic growth of our three deletion strains with either ammonium or nitrate. The rnfCDGEAB- and rseC-deletion strains failed to reduce nitrate as a metabolic activity in non-growing cultures during autotrophy but not during heterotrophy. In contrast, the nitrate reductase deletion strain was able to grow in all tested conditions but lost the ability to reduce nitrate. Our findings highlight the important role of the rseC gene for autotrophy and contribute to understand the connection of nitrate reduction to energy metabolism.

Plastoquinones in photosynthesis

1978 ◽  
Vol 284 (1002) ◽  
pp. 591-599 ◽  
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Energy Conservation ◽  
Thylakoid Membrane ◽  
Electron Flow ◽  
Proton Translocation ◽  
Photosynthetic Electron Transport ◽  
Atp Formation ◽  
Electron Transport Chains

Several plastoquinones with different or modified side chains have been characterized in plant material: they are localized in the inner thylakoid membrane of the chloroplast. So far only plastoquinone-45 (PQ-45) has been identified as an obligatory functional component of the photosynthetic electron transport chain in chloroplasts between photosystem II and photosystem I. A special form (semiquinone) of PQ-45 acts as primary acceptor Q of photosystem II, a large pool of PQ-45 as electron buffer, interconnecting several electron transport chains. The rôle of PQ, in energy conservation (ATP formation) is of particular current interest. Owing to vectorial electron flow across the thylakoid membrane, plastoquinone is thought to be reduced on the outside and plastohydroquinone to be oxidized on the inside of the membrane. This results in a proton translocation across the membrane and a build-up of a proton motive force which drives ATP formation. Old and new plastoquinone antagonists are described and the relevance of inhibitor studies on the rôle of plastoquinone in electron flow and photophosphorylation is discussed. Open questions and current problems of the mechanism of plastoquinone/plastoquinol transport across the membrane - and of proton translocation connected to it - relevant for the mechanism of energy conservation in photosynthesis, are pointed out.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

The role of ligands in electron transport in nanocrystal solids

Nanoscale ◽  
2020 ◽  
Vol 12 (45) ◽  
pp. 23028-23035
Author(s):  
Artem R. Khabibullin ◽  
Alexander L. Efros ◽  
Steven C. Erwin
Keyword(s):  
Electron Transport ◽  
Theoretical Modeling

Theoretical modeling of wavefunction overlap in nanocrystal solids elucidates the important role played by ligands in electron transport.

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