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Journal of Bacteriology, November 2007, p. 8250-8256, Vol. 189, No. 22
0021-9193/07/$08.00+0     doi:10.1128/JB.00752-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Isolated Poly(3-Hydroxybutyrate) (PHB) Granules Are Complex Bacterial Organelles Catalyzing Formation of PHB from Acetyl Coenzyme A (CoA) and Degradation of PHB to Acetyl-CoA{triangledown}

Keiichi Uchino,1,2 Terumi Saito,2 Birgit Gebauer,1 and Dieter Jendrossek1*

Institut für Mikrobiologie, Universität Stuttgart, Stuttgart, Germany,1 Laboratory of Molecular Microbiology, Kanagawa University, Kanagawa 259-1293, Japan2

Received 14 May 2007/ Accepted 10 August 2007

Poly(3-hydroxybutyrate) (PHB) granules isolated in native form (nPHB granules) from Ralstonia eutropha catalyzed formation of PHB from 14C-labeled acetyl coenzyme A (CoA) in the presence of NADPH and concomitantly released CoA, revealing that PHB biosynthetic proteins (acetoacetyl-CoA thiolase, acetoacetyl-CoA reductase, and PHB synthase) are present and active in isolated nPHB granules in vitro. nPHB granules also catalyzed thiolytic cleavage of PHB in the presence of added CoA, resulting in synthesis of 3-hydroxybutyryl-CoA (3HB-CoA) from PHB. Synthesis of 3HB-CoA was also shown by incubation of artificial (protein-free) PHB with CoA and PhaZa1, confirming that PhaZa1 is a PHB depolymerase catalyzing the thiolysis reaction. Acetyl-CoA was the major product detectable after incubation of nPHB granules in the presence of NAD+, indicating that downstream mobilizing enzyme activities were also present and active in isolated nPHB granules. We propose that intracellular concentrations of key metabolites (CoA, acetyl-CoA, 3HB-CoA, NAD+/NADH) determine whether a cell accumulates or degrades PHB. Since the degradation product of PHB is 3HB-CoA, the cells do not waste energy by synthesis and degradation of PHB. Thus, our results explain the frequent finding of simultaneous synthesis and breakdown of PHB.

* Corresponding author. Mailing address: Institut für Mikrobiologie, Universität Stuttgart, Allmandring 31, 70550 Stuttgart, Germany. Phone: 49-711-685-65483. Fax: 49-711-685-65725. E-mail: dieter.jendrossek{at}imb.uni-stuttgart.de

{triangledown} Published ahead of print on 24 August 2007.

Journal of Bacteriology, November 2007, p. 8250-8256, Vol. 189, No. 22
0021-9193/07/$08.00+0     doi:10.1128/JB.00752-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Chen, H.-J., Pan, S.-C., Shaw, G.-C. (2009). Identification and Characterization of a Novel Intracellular Poly(3-Hydroxybutyrate) Depolymerase from Bacillus megaterium. Appl. Environ. Microbiol. 75: 5290-5299 [Abstract] [Full Text]  
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  • Uchino, K., Saito, T., Jendrossek, D. (2008). Poly(3-Hydroxybutyrate) (PHB) Depolymerase PhaZa1 Is Involved in Mobilization of Accumulated PHB in Ralstonia eutropha H16. Appl. Environ. Microbiol. 74: 1058-1063 [Abstract] [Full Text]  


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