HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Supplementary figures Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Pauling, D. C. Articles by Ludwig, R. A. Search for Related Content PubMed PubMed Citation Articles by Pauling, D. C. Articles by Ludwig, R. A. Agricola Articles by Pauling, D. C. Articles by Ludwig, R. A.

Azorhizobium caulinodans pyruvate dehydrogenase activity is dispensable for aerobic but required for microaerobic growth^b

Department of MCD Biology, Sinsheimer Laboratories, University of California, Santa Cruz, CA 95064, USA¹

Author for correspondence: Robert A. Ludwig. Tel: +1 831 459 4084. e-mail: ludwig{at}darwin.ucsc.edu

Azorhizobium caulinodans mutant 62004 carries a null allele of pdhB, encoding the E1ß subunit of pyruvate dehydrogenase, which converts pyruvate to acetyl-CoA. This pdhB mutant completely lacks pyruvate oxidation activities yet grows aerobically on C₄ dicarboxylates (succinate, L-malate) as sole energy source, albeit slowly, and displays pleiotropic growth defects consistent with physiological acetyl-CoA limitation. Temperature-sensitive (ts), conditional-lethal derivatives of the pdhB mutant lack (methyl)malonate semialdehyde dehydrogenase activity, which thus also allows L-malate conversion to acetyl-CoA. The pdhB mutant remains able to fix N₂ in aerobic culture, but is unable to fix N₂ in symbiosis with host Sesbania rostrata plants and cannot grow microaerobically. In culture, A. caulinodans wild-type can use acetate, ß-D-hydroxybutyrate and nicotinate – all direct precursors of acetyl-CoA – as sole C and energy source for aerobic, but not microaerobic growth. Paradoxically, acetyl-CoA is thus a required intermediate for microaerobic oxidative energy transduction while not itself oxidized. Accordingly, A. caulinodans energy transduction under aerobic and microaerobic conditions is qualitatively different.

Keywords: (methyl)malonate semialdehyde dehydrogenase, microaerobiosis, Rhizobiaceae, microaerophilic bacteria

Abbreviations: DOT, dissolved O₂ tension; MSDH, (methyl)malonate semialdehyde dehydrogenase (acylating); PDH, pyruvate dehydrogenase; PHB, poly-ß-hydroxybutyrate

^b The GenBank accession number for the sequence determined in this work is AF299324.

This article has been cited by other articles:

				S. Laurent, J. Jang, A. Janicki, C.-C. Zhang, and S. Bedu Inactivation of spkD, encoding a Ser/Thr kinase, affects the pool of the TCA cycle metabolites in Synechocystis sp. strain PCC 6803 Microbiology, July 1, 2008; 154(7): 2161 - 2167. [Abstract] [Full Text] [PDF]

				J. D. Scott and R. A. Ludwig Azorhizobium caulinodans electron-transferring flavoprotein N electrochemically couples pyruvate dehydrogenase complex activity to N2 fixation Microbiology, January 1, 2004; 150(1): 117 - 126. [Abstract] [Full Text] [PDF]

				H. Grammel, E.-D. Gilles, and R. Ghosh Microaerophilic Cooperation of Reductive and Oxidative Pathways Allows Maximal Photosynthetic Membrane Biosynthesis in Rhodospirillum rubrum Appl. Envir. Microbiol., November 1, 2003; 69(11): 6577 - 6586. [Abstract] [Full Text] [PDF]

				M. F. Dunn, G. Araiza, S. Encarnacion, M. del Carmen Vargas, and J. Mora Effect of aniA (Carbon Flux Regulator) and phaC (Poly-{beta}-Hydroxybutyrate Synthase) Mutations on Pyruvate Metabolism in Rhizobium etli J. Bacteriol., April 15, 2002; 184(8): 2296 - 2299. [Abstract] [Full Text] [PDF]