Biosynthesis and thermal characterization of polyhydroxyalkanoates bearing phenyl and phenylalkyl side groups

Abstract

Polyhydroxyalkanoate (PHA) synthase 1 (PhaC1 Ps) from Pseudomonas sp. 61-3 is a broad-substrate-specific enzyme. In this study, by employing Ralstonia eutropha PHB-4 recombinant expressing PhaC1 Ps , a novel type of 3-hydroxybutyrate (3HB)-based PHA copolymer, poly(3HB-co-3-hydroxy-3-phenylpropionate) [P(3HB-co-3H3PhP)], bearing phenyl side groups, was synthesized. The 3H3PhP fraction was increased up to 8.9 mol% by feeding 3H3PhP precursors. As the phenyl side group was introduced into P(3HB), the melting temperature and the enthalpy of fusion decreased, while the glass transition temperature (T g) increased, demonstrating a distinct thermal behavior as a result of the phenyl side group. Furthermore, PHAs bearing phenylalkyl side groups were synthesized from -phenylalkanoates by Pseudomonas putida KT2440, and their thermal properties were characterized. Based on the measured and predicted T g values, the effect of the acyl chain length in the aromatic side group on T g was investigated. This study demonstrates the role that aromatic side groups play in the thermal properties of PHAs.

Valorisation of local agro-industrial processing waters as growth media for polyhydroxyalkanoates (PHA) production

“…The thermal characteristics of PHA copolymers strongly depend on the type, content and distribution of comonomer units comprising the polymer chains, as well as the average molecular weight and molecular weight distribution. The glass transition is influenced by the size of the side group and generally, the observed relationship suggests that an increase in the alkyl chain size of the side group causes steric hindrance and results in a decrease in T g , mainly due to an increase in the free volume [21]. The higher of alkyl chain length, the lower the T g of the PHA.…”

Biosynthesis and Characteristics of Aromatic Polyhydroxyalkanoates

“…Incorporation of most of the monomers shown in Figure 1 into PHA chains was achieved using Pseudomonas strains. Although there are some reports of the production of aromatic PHAs using recombinant Escherichia coli and R. eutropha [15,16,17,18], these cases also required PHA synthase from Pseudomonas . To the best of our knowledge, only PHA synthase from Pseudomonas can polymerize aromatic monomers.…”

“…Generally, to generate aromatic PHAs, defined compounds containing aromatic groups are added to the medium as a precursor (i.e., 5PhV or 5-phenyl-2,4-pentadienoic acid is used as a precursor to produce PHAs containing 3H5PhV [14,15,19,20]). However, there are a few reports on the production of aromatic PHAs without any supplementation with these defined aromatic compounds [16,18].…”

Bioconversion of lignin and its derivatives into polyhydroxyalkanoates: Challenges and opportunities

“…This was identified by the presence of 3‐hydroxy‐3‐phenylpropionate monomers within the aromatic PHA polymer. A maximum of 27% PHA accumulation was observed within 72 H of cultivation . It was a unique study where aromatic PHA copolymer was produced by integrating the metabolic capabilities of R. eutropha and tethering properties of PHA synthase from Pseudomonas .…”

“…Cinnamic acid, 3‐hydroxyphenyl propionic acid, and phenylacetic acid are several potential derivatives released during lignin hydrolysis. They have been explored for the synthesis of PHA containing aromatic monomers that consequently diversify its potential applications . 3‐Hydroxyphenyl propionic acid was used for aromatic PHA production, whereas styrene and phenylacetic acid could only lead to aliphatic PHA monomers .…”