title: Biosynthesis of polyhydroxyalkanoate copolymers from methanol by Methylobacterium extorquens AM1 and the engineered strains under cobalt-deficient conditions.
abstract: Methylobacterium extorquens AM1 has been shown to accumulate polyhydroxyalkanoate (PHA) composed solely of (R)-3-hydroxybutyrate (3HB) during methylotrophic growth. The present study demonstrated that the wild-type strain AM1 grown under Co²⁺-deficient conditions accumulated copolyesters of 3HB and a C₅-monomer, (R)-3-hydroxyvalerate (3HV), using methanol as the sole carbon source. The 3HV unit was supposed to be derived from propionyl-CoA, synthesized via the ethylmalonyl-CoA pathway impaired by Co²⁺ limitation. This assumption was strongly supported by the dominant incorporation of the 3HV unit into PHA when a strain lacking propionyl-CoA carboxylase was incubated with methanol. Further genetic engineering of M. extorquens AM1 was employed for the methylotrophic synthesis of PHA copolymers. A recombinant strain of M. extorquens AM1C(Ac) in which the original PHA synthase gene phaC(Me) had been replaced by phaC(Ac), encoding an enzyme with broad substrate specificity from Aeromonas caviae, produced a PHA terpolymer composed of 3HB, 3HV, and a C₆-monomer, (R)-3-hydroxyhexanoate, from methanol. The cellular content and molecular weight of the PHA accumulated in the strain AM1C(Ac) were higher than those of PHA in the wild-type strain. The triple deletion of three PHA depolymerase genes in M. extorquens AM1C(Ac) showed no significant effects on growth and PHA biosynthesis properties. Overexpression of the genes encoding β-ketothiolase and NADPH-acetoacetyl-CoA reductase increased the cellular PHA content and 3HV composition in PHA, although the cell growth on methanol was decreased. This study opens up the possibility of producing practical PHA copolymers with methylotrophic bacteria using methanol as a feedstock.
authors.affiliation: Department of Bioengineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8501, Japan.
authors.forename: Izumi
authors.initials: I
authors.lastname: Orita
authors.forename: Kouta
authors.initials: K
authors.lastname: Nishikawa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nakamura
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Fukui
mesh_terms: D057585:Aeromonas caviae / Q000201:enzymology / Q000235:genetics; D003035:Cobalt / Q000378:metabolism*; D017353:Gene Deletion; D015870:Gene Expression; D060847:Metabolic Engineering; D000432:Methanol / Q000378:metabolism*; D020601:Methylobacterium extorquens / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D011091:Polyesters / Q000378:metabolism*; D054813:Polyhydroxyalkanoates / Q000096:biosynthesis*; D014631:Valerates / Q000378:metabolism*; D000094122:Polyhydroxybutyrates
chemical_list: D003035:Cobalt; D000432:Methanol; D011091:Polyesters; D054813:Polyhydroxyalkanoates; D014631:Valerates; C052620:poly(3-hydroxybutyrate)-co-(3-hydroxyvalerate); D000094122:Polyhydroxybutyrates; C488798:poly(3-hydroxycaproate); C073314:poly(3-hydroxyvalerate)