Biosynthesis and Characterization of Polyhydroxyalkanoates with Controlled Composition and Microstructure.

Area of Science:

• Microbiology
• Polymer Science
• Biotechnology

Background:

• Polyhydroxyalkanoates (PHAs) are biodegradable polyesters with diverse applications.
• Controlling the composition and microstructure of PHAs is crucial for tailoring their properties.
• Haloferax mediterranei is a halophilic archaeon capable of producing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV).

Purpose of the Study:

• To investigate the production of PHBV with controllable composition and microstructure using volatile fatty acids (VFA) as the sole carbon source in Haloferax mediterranei.
• To synthesize bespoke random, block, and blend copolymers with varying 3-hydroxyvalerate (3HV) fractions.
• To evaluate the impact of VFA feeding strategies on PHBV properties.

Main Methods:

• Cultivation of Haloferax mediterranei using C2:0 to C6:0 volatile fatty acids (VFA) as sole carbon sources.
• Utilizing mixtures of C4:0 and C5:0 VFA to control the 3-hydroxyvalerate (3HV) content in PHBV.
• Varying substrate addition order (cofeding vs. sequential feeding) to influence copolymer microstructure (random, block, blend).

Main Results:

• Carbon-even VFA (e.g., C4:0) resulted in >90 mol% poly(3-hydroxybutyrate) (3HB) PHBV.
• Carbon-odd VFA (e.g., C5:0) generated >87 mol% poly(3-hydroxyvalerate) (3HV) PHBV.
• The 3HV fraction was directly proportional to the %C5:0 in the feed mixture.
• Sequential feeding produced block and blend copolymers, while cofeeding yielded random copolymers.
• Synthesized PHBV exhibited an ultrahigh average molecular weight of 3 × 10^6 g/mol.
• 3HV-rich copolymers displayed lower melting temperatures, enhanced elasticity, and ductility.

Conclusions:

• Haloferax mediterranei is suitable for large-scale PHBV production due to its bioprocessing advantages.
• Precise control over PHBV composition and microstructure is achievable by manipulating VFA feeding strategies.
• Tailored PHBV copolymers can be produced to meet specific industrial application criteria.