Characterization of an (R)-specific enoyl-CoA hydratase from Streptomyces sp. strain CFMR 7: A metabolic tool for enhancing the production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Superlative short chain length and medium chain length polyhydroxyalkanoates microbial producers isolated from Malaysian environment

Plastic waste pollution is escalating globally at an unprecedented pace, with a significant measure of this waste remaining unrecycled. Hence, polyhydroxyalkanoates (PHAs), a biogenic polyester, as a potential alternative to synthetic plastics has been intensively studied over the years. PHAs are biodegradable and biocompatible polyester produced by various microorganisms through the bioprocessing of sustainable sources. Bacterial PHAs show potential as an eco-friendly, biodegradable, and biocompatible alternative to conventional plastics. Malaysian environment, anthropogenic and natural, harbors an enormous diversity of microorganisms as well as various bacteria that produce PHAs. Hence, the current submission highlights on four indigenous PHA producers, isolated from the local environments, namely Cupriavidus malaysiensis USMAA2-4, Cupriavidus malaysiensis USMAA10-20, Cupriavidus malaysiensis USMAHM13, and Pseudomonas putida BET001. The four strains have contributed significantly as a workhorse in advancing PHA research and innovation in Malaysia and globally. Their uniqueness and significance in the PHA investigation, which include biosynthesis, recovery strategies, metabolic pathways involved, characteristics and properties of extracted PHA, biodegradation, and its potential applications are discussed.

Strategic Use of Vegetable Oil for Mass Production of 5-Hydroxyvalerate-Containing Polyhydroxyalkanoate from δ-Valerolactone by Engineered Cupriavidus necator

Although efforts have been undertaken to produce polyhydroxyalkanoates (PHA) with various monomers, the low yield of PHAs because of complex metabolic pathways and inhibitory substrates remains a major hurdle in their analyses and applications. Therefore, we investigated the feasibility of mass production of PHAs containing 5-hydroxyvalerate (5HV) using δ-valerolactone (DVL) without any pretreatment along with the addition of plant oil to achieve enough biomass. We identified that PhaCBP-M-CPF4, a PHA synthase, was capable of incorporating 5HV monomers and that C. necator PHB-4 harboring phaCBP-M-CPF4 synthesized poly(3HB-co-3HHx-co-5HV) in the presence of bean oil and DVL. In fed-batch fermentation, the supply of bean oil resulted in the synthesis of 49 g/L of poly(3HB-co-3.7 mol% 3HHx-co-5.3 mol%5HV) from 66 g/L of biomass. Thermophysical studies showed that 3HHx was effective in increasing the elongation, whereas 5HV was effective in decreasing the melting point. The contact angles of poly(3HB-co-3HHx-co-5HV) and poly(3HB-co-3HHx) were 109 and 98°, respectively. In addition, the analysis of microbial degradation confirmed that poly(3HB-co-3HHx-co-5HV) degraded more slowly (82% over 7 days) compared to poly(3HB-co-3HHx) (100% over 5 days). Overall, the oil-based fermentation strategy helped produce more PHA, and the mass production of novel PHAs could provide more opportunities to study polymer properties.

Controlled production of a polyhydroxyalkanoate (PHA) tetramer containing different mole fraction of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3 HV), 4 HV and 5 HV units by engineered Cupriavidus necator

Polyhydroxyalkanoates (PHAs) are promising alternatives to existing petrochemical-based plastics because of their bio-degradable properties. However, the limited structural diversity of PHAs has hindered their application. In this study, high mole-fractions of Poly (39 mol% 3HB-co-17 mol% 3 HV-co-44 mol% 4 HV) and Poly (25 mol% 3HB-co-75 mol% 5 HV) were produced from 4- hydroxyvaleric acid and 5-hydroxyvaleric acid, using Cupriavidus necator PHB-4 harboring the gene phaCBP-M-CPF4 with modified sequences. In addition, the complex toxicity of precursor mixtures was tested, and it was confirmed that the engineered C. necator was capable of synthesizing Poly (32 mol% 3HB-co-11 mol% 3 HV-co-25 mol% 4 HV-co-32 mol% 5 HV) at low mixture concentrations. Correlation analyses of the precursor ratio and the monomeric mole fractions indicated that each mole fractions could be precisely controlled using the precursor proportion. Physical property analysis confirmed that Poly (3HB-co-3 HV-co-4 HV) is a rubber-like amorphous polymer and Poly (3HB-co-5 HV) has a high tensile strength and elongation at break. Poly (3HB-co-3 HV-co-4 HV-co-5 HV) had a much lower glass transition temperature than the co-, terpolymers containing 3 HV, 4 HV and 5 HV. This study expands the range of possible physical properties of PHAs and contributes to the realization of custom PHA production by suggesting a method for producing PHAs with various physical properties through mole-fraction control of 3 HV, 4 HV and 5 HV.

Maximization of 3-hydroxyhexanoate fraction in poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) using lauric acid with engineered Cupriavidus necator H16

As polyhydroxybutyrate (P(3HB)) was struggling with mechanical properties, efforts have been directed towards increasing mole fraction of 3-hydroxyhexanoate (3HHx) in P(3HB-co-3HHx) to improve the properties of polyhydroxyalkanoates (PHAs). Although genetic modification had significant results, there were several issues related to cell growth and PHA production by deletion of PHA synthetic genes. To find out easier strategy for high 3HHx mole fraction without gene deletion, Cupriavidus necator H16 containing phaC2Ra-phaACn-phaJ1Pa was examined with various oils resulting that coconut oil gave the highest 3HHx mole fraction. When fatty acid composition analysis with GC-MS was applied, coconut oil was found to have very different composition from other vegetable oil containing very high lauric acid (C12) content. To find out specific fatty acid affecting 3HHx fraction, different fatty acids from caproic acid (C6) to stearic acid (C18) was evaluated and the 3HHx mole fraction was increased to 26.5 ± 1.6 % using lauric acid. Moreover, the 3HHx mole fraction could be controlled from 9 % to 31.1 % by mixing bean oil and lauric acid with different ratios. Produced P(3HB-co-3HHx) exhibited higher molecular than P(3HB-co-3HHx) from phaB-deletion mutant. This study proposes another strategy to increase 3HHx mole fraction with easier way by modifying substrate composition without applying deletion tools.

A review on poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] and genetic modifications that affect its production

Polyhydroxyalkanoates (PHAs) have garnered global attention to replace petroleum-based plastics in certain applications due to their biodegradability and sustainability. Among the different types of PHAs, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] copolymer has similar properties to commodity plastics, making them a suitable candidate to replace certain types of single-use plastics, medical devices, and packaging materials. The degradation rate of P(3HB-co-3HHx) is faster than the commercial petroleum-based plastics which take a very long time to be degraded, causing harmful pollution to both land and marine ecosystem. The biodegradability of the P(3HB-co-3HHx) is also dependent on its 3HHx molar composition which in turn influences the crystallinity of the material. Various metabolic pathways like the common PHA biosynthesis pathway, which involves phaA, phaB, and phaC, β-oxidation, and fatty acids de novo synthesis are used by bacteria to produce PHA from different carbon sources like fatty acids and sugars, respectively. There are various factors affecting the 3HHx molar composition of P(3HB-co-3HHx), like PhaCs, the engineering of PhaCs, and the metabolic engineering of strains. It is crucial to control the 3HHx molar composition in the P(3HB-co-3HHx) as it will affect its properties and applications in different fields.