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Applied and Environmental Microbiology, October 2009, p. 6168-6175, Vol. 75, No. 19
0099-2240/09/$08.00+0     doi:10.1128/AEM.00938-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Identification of the Polyhydroxyalkanoate (PHA)-Specific Acetoacetyl Coenzyme A Reductase among Multiple FabG Paralogs in Haloarcula hispanica and Reconstruction of the PHA Biosynthetic Pathway in Haloferax volcanii{triangledown} ,{dagger}

Jing Han, Qiuhe Lu, Ligang Zhou,{ddagger} Hailong Liu, and Hua Xiang*

State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, People's Republic of China

Received 27 April 2009/ Accepted 23 July 2009

Genome-wide analysis has revealed abundant FabG (β-ketoacyl-ACP reductase) paralogs, with uncharacterized biological functions, in several halophilic archaea. In this study, we identified for the first time that the fabG1 gene, but not the other five fabG paralogs, encodes the polyhydroxyalkanoate (PHA)-specific acetoacetyl coenzyme A (acetoacetyl-CoA) reductase in Haloarcula hispanica. Although all of the paralogous fabG genes were actively transcribed, only disruption or knockout of fabG1 abolished PHA synthesis, and complementation of the {Delta}fabG1 mutant with the fabG1 gene restored both PHA synthesis capability and the NADPH-dependent acetoacetyl-CoA reductase activity. In addition, heterologous coexpression of the PHA synthase genes (phaEC) together with fabG1, but not its five paralogs, reconstructed the PHA biosynthetic pathway in Haloferax volcanii, a PHA-defective haloarchaeon. Taken together, our results indicate that FabG1 in H. hispanica, and possibly its counterpart in Haloarcula marismortui, has evolved the distinct function of supplying precursors for PHA biosynthesis, like PhaB in bacteria. Hence, we suggest the renaming of FabG1 in both genomes as PhaB, the PHA-specific acetoacetyl-CoA reductase of halophilic archaea.

* Corresponding author. Mailing address: State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 West Beichen Road, Chaoyang District, Beijing 100101, People's Republic of China. Phone and fax: (86) 10-6480-7472. E-mail: xiangh{at}sun.im.ac.cn

{triangledown} Published ahead of print on 31 July 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

{ddagger} Present address: Department of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, TX 78712.

Applied and Environmental Microbiology, October 2009, p. 6168-6175, Vol. 75, No. 19
0099-2240/09/$08.00+0     doi:10.1128/AEM.00938-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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