PHBHV Biosynthesis by Haloferax mediterranei: from Genetics, Metabolism, and Engineering to Economical Production

The halophilic archaeon Haloferax mediterranei, has shown promise for the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV), a desirable bioplastic, from many low-cost carbon sources. To obtain a full understanding of PHBHV biosynthesis and to provide novel strategies for polyhydroxyalkanaote (PHA) production by haloarchaea, the complete genome of H. mediterranei has been determined, and a genome-wide investigation of the genetics and metabolism of this haloarchaeon involved in PHBHV biosynthesis was performed in the past few years. This exploration covers the identification of key genes for PHBHV biosynthesis, the specific precursor supplying pathways, the PHA granule modulation, and PHBHV mobilization, as well as its linkage to haloarchaeal-specific acetyl-CoA and propionyl- CoA assimilation. These advances have not only revealed many haloarchaeal-specific enzymes and pathways for PHBHV biosynthesis, such as the archaeal-type PHA synthases, the haloarchaeal-type β-ketothiolases with two distinct subunits, and the novel 3-hydroxypropionate pathway coupling CO2 fixation into PHBHV, but have also provided strategies for bioengineering haloarchaea for economical production of PHBHV or tailor-made higher-value PHA. This chapter will summarize these current progresses of PHBHV biosynthesis by H. mediterranei, thus providing a perspective for economical production of industry-scale or higher-value PHAs by haloarchaea in the near future.

Keywords: Acetoacetyl-CoA reductase, Acetyl-CoA, β-ketothiolase, β-oxidation, Carbon sources, Copolyester, Economical production, Genes, Genome, Haloferax mediterranei, Halophilic archaea, PHA biosynthesis, PHA depolymerase, PHA granule, PHA mobilization, PHA synthase, Polyhydroxyalkanoates (PHA), Poly(3-hydroxybutyrate-co- 3-hydroxyvalerate) (PHBHV), Propionyl-CoA, Regulation, Tailor-made PHA, Terpolyester.