This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lemos, P. C. Articles by Santos, H. Search for Related Content PubMed PubMed Citation Articles by Lemos, P. C. Articles by Santos, H. Agricola Articles by Lemos, P. C. Articles by Santos, H.

 Previous Article  |  Next Article 

Applied and Environmental Microbiology, January 2003, p. 241-251, Vol. 69, No. 1
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.1.241-251.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Metabolic Pathway for Propionate Utilization by Phosphorus-Accumulating Organisms in Activated Sludge: ¹³C Labeling and In Vivo Nuclear Magnetic Resonance

Paulo C. Lemos,^1,2 Luísa S. Serafim,² Margarida M. Santos,² Maria A. M. Reis,² and Helena Santos^1*

Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, 2870-156 Oeiras,¹ Chemistry Department, CQFB/Requimte, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal²

Received 19 June 2002/ Accepted 25 October 2002

In vivo ¹³C and ³¹P nuclear magnetic resonance techniques were used to study propionate metabolism by activated sludge in enhanced biological phosphorus removal systems. The fate of label supplied in [3-¹³C]propionate was monitored in living cells subjected to anaerobic/aerobic cycles. During the anaerobic phase, propionate was converted to polyhydroxyalkanoates (PHA) with the following monomer composition: hydroxyvalerate, 74.2%; hydroxymethylvalerate, 16.9%; hydroxymethylbutyrate, 8.6%; and hydroxybutyrate, 0.3%. The isotopic enrichment in the different carbon atoms of hydroxyvalerate (HV) produced during the first anaerobic stage was determined: HV₅, 59%; HV₄, 5.0%; HV₃, 1.1%; HV₂, 3.5%; and HV₁, 2.8%. A large proportion of the supplied label ended up on carbon C-5 of HV, directly derived from the pool of propionyl-coenzyme A (CoA), which is primarily labeled on C-3; useful information on the nature of operating metabolic pathways was provided by the extent of labeling on C-1, C-2, and C-4. The labeling pattern on C-1 and C-2 was explained by the conversion of propionyl-CoA to acetyl-CoA via succinyl-CoA and the left branch of the tricarboxylic acid cycle, which involves scrambling of label between the inner carbons of succinate. This constitutes solid evidence for the operation of succinate dehydrogenase under anaerobic conditions. The labeling in HV₄ is explained by backflux from succinate to propionyl-CoA. The involvement of glycogen in the metabolism of propionate was also demonstrated; moreover, it was shown that the acetyl moiety to the synthesis of PHA was derived preferentially from glycogen. According to the proposed metabolic scheme, the decarboxylation of pyruvate is coupled to the production of hydrogen, and the missing reducing equivalents should be derived from a source other than glycogen metabolism.

---

* Corresponding author. Mailing address: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, 2870-156 Oeiras, Portugal. Phone: 351 21 4469800. Fax: 351 21 4428766. E-mail: santos{at}itqb.unl.pt.

---

Applied and Environmental Microbiology, January 2003, p. 241-251, Vol. 69, No. 1
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.1.241-251.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.