Multiple Propionyl Coenzyme A-Supplying Pathways for Production of the Bioplastic Poly(3-Hydroxybutyrate- co -3-Hydroxyvalerate) in Haloferax mediterranei

• DOI: 10.1128/aem.03915-12
• Publication Date: 2013-02-23T12:18:49Z
• Authors: Jing Han; Jing Hou; Fan Zhang; Guomin Ai; Ming Li; Shuangfeng Cai; Hailong Liu; Lei Wang; Zejian Wang; Siliang Zhang; Lei Cai; Dahe Zhao; Jian Zhou; Hua Xiang
• Keywords: Carbon Isotopes; 0303 health sciences; Magnetic Resonance Spectroscopy; Archaeal Proteins; Gene Expression Profiling; Polyesters; Haloferax mediterranei; Computational Biology; Down-Regulation; Carbon Dioxide; Biosynthetic Pathways; Carbon Cycle; Gene Knockout Techniques; 03 medical and health sciences; Glucose; Genome, Archaeal; Sequence Analysis, Protein; Acyl Coenzyme A; Gene Expression Regulation, Archaeal; Pentanoic Acids; Oligonucleotide Array Sequence Analysis; Sequence Deletion

ABSTRACT

Haloferax mediterranei is able to accumulate the bioplastic poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) with more than 10 mol% 3-hydroxyvalerate (3HV) from unrelated carbon sources. However, the pathways that produce propionyl coenzyme A (propionyl-CoA), an important precursor of 3HV monomer, have not yet been determined. Bioinformatic analysis of H. mediterranei genome indicated that this strain uses multiple pathways for propionyl-CoA biosynthesis, including the citramalate/2-oxobutyrate pathway, the aspartate/2-oxobutyrate pathway, the methylmalonyl-CoA pathway, and a novel 3-hydroxypropionate pathway. Cofeeding of pathway intermediates and inactivating pathway-specific genes supported that these four pathways were indeed involved in the biosynthesis of 3HV monomer. The novel 3-hydroxypropionate pathway that couples CO 2 assimilation with PHBV biosynthesis was further confirmed by analysis of 13 C positional enrichment in 3HV. Notably, 13 C metabolic flux analysis showed that the citramalate/2-oxobutyrate pathway (53.0% flux) and the 3-hydroxypropionate pathway (30.6% flux) were the two main generators of propionyl-CoA from glucose. In addition, genetic perturbation on the transcriptome of the Δ phaEC mutant (deficient in PHBV accumulation) revealed that a considerable number of genes in the four propionyl-CoA synthetic pathways were significantly downregulated. We determined for the first time four propionyl-CoA-supplying pathways for PHBV production in haloarchaea, particularly including a new 3-hydroxypropionate pathway. These results would provide novel strategies for the production of PHBV with controllable 3HV molar fraction.