scholarly journals A Soluble NADH-Dependent Fumarate Reductase in the Reductive Tricarboxylic Acid Cycle of Hydrogenobacter thermophilus TK-6

2008 ◽  
Vol 190 (21) ◽  
pp. 7170-7177 ◽  
Author(s):  
Akane Miura ◽  
Masafumi Kameya ◽  
Hiroyuki Arai ◽  
Masaharu Ishii ◽  
Yasuo Igarashi
Keyword(s):  
Soluble Fraction ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Fumarate Reductase ◽  
High Sequence Identity ◽  
Catalytic Subunits ◽  
Acid Cycle ◽  
Genes Encoding ◽  
Hydrogenobacter Thermophilus ◽  
Reductive Tricarboxylic Acid Cycle

ABSTRACT Fumarate reductase (FRD) is an enzyme that reduces fumarate to succinate. In many organisms, it is bound to the membrane and uses electron donors such as quinol. In this study, an FRD from a thermophilic chemolithoautotrophic bacterium, Hydrogenobacter thermophilus TK-6, was purified and characterized. FRD activity using NADH as an electron donor was not detected in the membrane fraction but was found in the soluble fraction. The purified enzyme was demonstrated to be a novel type of FRD, consisting of five subunits. One subunit showed high sequence identity to the catalytic subunits of known FRDs. Although the genes of typical FRDs are assembled in a cluster, the five genes encoding the H. thermophilus FRD were distant from each other in the genome. Furthermore, phylogenetic analysis showed that the H. thermophilus FRD was located in a distinct position from those of known soluble FRDs. This is the first report of a soluble NADH-dependent FRD in Bacteria and of the purification of a FRD that operates in the reductive tricarboxylic acid cycle.

scholarly journals The pathway of glycollate utilization in Chlorella pyrenoidosa

1970 ◽  
Vol 117 (5) ◽  
pp. 929-937 ◽  
Author(s):  
J. M. Lord ◽  
M. J. Merrett
Keyword(s):  
Soluble Fraction ◽  
Tricarboxylic Acid Cycle ◽  
Experimental Period ◽  
Chlorella Pyrenoidosa ◽  
Total Radioactivity ◽  
Tricarboxylic Acid ◽  
Short Term ◽  
Acid Cycle ◽  
Metabolic Sequence ◽  
Specific Activities

1. Exogenous glycollate was rapidly metabolized in both the light and the dark by photoautotrophically grown Chlorella pyrenoidosa. 2. The incorporation of 14C from [1-14C]glycollate by these cells was inhibited by the tricarboxylic acid-cycle inhibitors monofluoroacetate, diethylmalonate and arsenite, and also by α-hydroxypyrid-2-ylmethanesulphonate and isonicotinylhydrazine. 3. Short-term kinetic experiments showed over 80% of the total 14C present in the soluble fraction from the cells to be in glycine and serine after 10s. This percentage decreased with time whereas the percentage radioactivity in glycerate increased for up to 30s then remained steady. The percentage of the total radioactivity present in citrate increased over the experimental period. Malate was the only other tricarboxylic acid-cycle intermediate to become labelled. 4. The kinetic and inhibitor experiments supported the following pathway of glycollate incorporation: glycollate → glyoxylate → glycine → serine → hydroxypyruvate → glycerate → 3-phosphoglycerate → 2-phosphoglycerate → phosphoenolpyruvate → pyruvate → acetyl-CoA. 5. The specific activities of the enzymes catalysing this metabolic sequence in cell-free extracts were great enough to account for the observed rate of glycollate metabolism of 0.25μmol/h per mg dry wt. of cells in the light.

scholarly journals Complete Genome Sequence of the Thermophilic, Obligately Chemolithoautotrophic Hydrogen-Oxidizing Bacterium Hydrogenobacter thermophilus TK-6

2010 ◽  
Vol 192 (10) ◽  
pp. 2651-2652 ◽  
Author(s):  
Hiroyuki Arai ◽  
Haruna Kanbe ◽  
Masaharu Ishii ◽  
Yasuo Igarashi
Keyword(s):  
Genome Sequence ◽  
Complete Genome Sequence ◽  
Complete Genome ◽  
Molecular Hydrogen ◽  
Elemental Sulfur ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Hydrogenobacter Thermophilus ◽  
Reductive Tricarboxylic Acid Cycle ◽  
Sole Energy

ABSTRACT Hydrogenobacter thermophilus is a thermophilic, obligately chemolithoautotrophic and aerobic hydrogen-oxidizing bacterium. It is unique in its ability to fix carbon dioxide via the reductive tricarboxylic acid cycle under aerobic conditions. It utilizes molecular hydrogen, elemental sulfur, or thiosulfate as the sole energy source. Here, we report the complete genome sequence of H. thermophilus TK-6.

scholarly journals Systems-informed genome mining for electroautotrophic microbial production

2020 ◽  
Author(s):  
Anthony J. Abel ◽  
Jacob M. Hilzinger ◽  
Adam P. Arkin ◽  
Douglas S. Clark
Keyword(s):  
Carbon Fixation ◽  
Microbial Respiration ◽  
Tricarboxylic Acid Cycle ◽  
Genome Mining ◽  
Tricarboxylic Acid ◽  
Nitrate Respiration ◽  
Fixation Rate ◽  
Acid Cycle ◽  
Carbon Molecules ◽  
Reductive Tricarboxylic Acid Cycle

AbstractMicrobial electrosynthesis (MES) systems can store renewable energy and CO2 in many-carbon molecules inaccessible to abiotic electrochemistry. Here, we develop a multiphysics model to investigate the fundamental and practical limits of MES enabled by direct electron uptake and we identify organisms in which this biotechnological CO2-fixation strategy can be realized. Systematic model comparisons of microbial respiration and carbon fixation strategies revealed that, under aerobic conditions, the CO2 fixation rate is limited to <6 μmol/cm2/hr by O2 mass transport despite efficient electron utilization. In contrast, anaerobic nitrate respiration enables CO2 fixation rates >50 μmol/cm2/hr for microbes using the reductive tricarboxylic acid cycle. Phylogenetic analysis, validated by recapitulating experimental demonstrations of electroautotrophy, uncovered multiple probable electroautotrophic organisms and a significant number of genetically tractable strains that require heterologous expression of <5 proteins to gain electroautotrophic function. The model and analysis presented here will guide microbial engineering and reactor design for practical MES systems.

scholarly journals A Novel Ferredoxin-Dependent Glutamate Synthase from the Hydrogen-Oxidizing Chemoautotrophic Bacterium Hydrogenobacter thermophilus TK-6

2007 ◽  
Vol 189 (7) ◽  
pp. 2805-2812 ◽  
Author(s):  
Masafumi Kameya ◽  
Takeshi Ikeda ◽  
Miyuki Nakamura ◽  
Hiroyuki Arai ◽  
Masaharu Ishii ◽  
...  
Keyword(s):  
Nitrogen Assimilation ◽  
Tricarboxylic Acid Cycle ◽  
Glutamate Synthase ◽  
Tricarboxylic Acid ◽  
Electron Donors ◽  
Plant Type ◽  
Central Carbon ◽  
Hydrogenobacter Thermophilus ◽  
Reductive Tricarboxylic Acid Cycle ◽  
Glutaminase Activity

ABSTRACT Glutamate synthases are classified according to their specificities for electron donors. Ferredoxin-dependent glutamate synthases had been found only in plants and cyanobacteria, whereas many bacteria have NADPH-dependent glutamate synthases. In this study, Hydrogenobacter thermophilus, a hydrogen-oxidizing chemoautotrophic bacterium, was shown to possess a ferredoxin-dependent glutamate synthase like those of phototrophs. This is the first observation, to our knowledge, of a ferredoxin-dependent glutamate synthase in a nonphotosynthetic organism. The purified enzyme from H. thermophilus was shown to be a monomer of a 168-kDa polypeptide homologous to ferredoxin-dependent glutamate synthases from phototrophs. In contrast to known ferredoxin-dependent glutamate synthases, the H. thermophilus glutamate synthase exhibited glutaminase activity. Furthermore, this glutamate synthase did not react with a plant-type ferredoxin (Fd3 from this bacterium) containing a [2Fe-2S] cluster but did react with bacterial ferredoxins (Fd1 and Fd2 from this bacterium) containing [4Fe-4S] clusters. Interestingly, the H. thermophilus glutamate synthase was activated by some of the organic acids in the reductive tricarboxylic acid cycle, the central carbon metabolic pathway of this organism. This type of activation has not been reported for any other glutamate synthases, and this property may enable the control of nitrogen assimilation by carbon metabolism.

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