Contribution of the bacterial endosymbiont to the biosynthesis of pyrimidine nucleotides in the deep-sea tube worm Riftia pachyptila.
The deep-sea tube worm Riftia pachyptila (Vestimentifera) from hydrothermal vents lives in an intimate symbiosis with a sulfur-oxidizing bacterium. That involves specific interactions and obligatory metabolic exchanges between the two organisms. In this work, we analyzed the contribution of the two partners to the biosynthesis of pyrimidine nucleotides through both the "de novo" and "salvage" pathways. The first three enzymes of the de novo pathway, carbamyl-phosphate synthetase, aspartate transcarbamylase, and dihydroorotase, were present only in the trophosome, the symbiont-containing tissue. The study of these enzymes in terms of their catalytic and regulatory properties in both the trophosome and the isolated symbiotic bacteria provided a clear indication of the microbial origin of these enzymes. In contrast, the succeeding enzymes of this de novo pathway, dihydroorotate dehydrogenase and orotate phosphoribosyltransferase, were present in all body parts of the worm. This finding indicates that the animal is fully dependent on the symbiont for the de novo biosynthesis of pyrimidines. In addition, it suggests that the synthesis of pyrimidines in other tissues is possible from the intermediary metabolites provided by the trophosomal tissue and from nucleic acid degradation products since the enzymes of the salvage pathway appear to be present in all tissues of the worm. Analysis of these salvage pathway enzymes in the trophosome strongly suggested that these enzymes belong to the worm. In accordance with this conclusion, none of these enzyme activities was found in the isolated bacteria. The enzymes involved in the production of the precursors of carbamyl phosphate and nitrogen assimilation, glutamine synthetase and nitrate reductase, were also investigated, and it appears that these two enzymes are present in the bacteria.
Minic
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Laboratoire de Biochimie des Signaux Régulateurs Cellulaires et Moléculaires, UMR 7631, CNRS, Université Pierre et Marie Curie, 96 Boulevard Raspail, F-75006 Paris, France.
Simon
V
V
Penverne
B
B
Gaill
F
F
Hervé
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G
D000818:Animals; D001221:Aspartate Carbamoyltransferase / Q000378:metabolism; D001419:Bacteria / Q000201:enzymology / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D002222:Carbamoyl-Phosphate Synthase (Ammonia) / Q000378:metabolism; D002852:Chromatography, Ion Exchange; D004080:Dihydroorotase / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D007448:Invertebrates / Q000033:anatomy & histology / Q000201:enzymology / Q000378:metabolism* / Q000382:microbiology*; D008954:Models, Biological; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D009963:Orotic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D011742:Pyrimidine Nucleotides / Q000096:biosynthesis*; D012623:Seawater; D013559:Symbiosis; D014020:Tissue Extracts / Q000032:analysis
D001426:Bacterial Proteins; D011742:Pyrimidine Nucleotides; D014020:Tissue Extracts; C004768:4,5-dihydroorotic acid; D009963:Orotic Acid; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D001221:Aspartate Carbamoyltransferase; D004080:Dihydroorotase; D005974:Glutamate-Ammonia Ligase; D002222:Carbamoyl-Phosphate Synthase (Ammonia)