Production of poly-(beta-hydroxybutyric-co-beta-hydroxyvaleric) acids

Area of Science:

• Microbiology
• Biotechnology
• Polymer Science

Background:

• Certain bacterial species naturally accumulate polyhydroxyalkanoates (PHAs) as intracellular carbon and energy storage polymers.
• Poly-beta-hydroxybutyric acid (PHB) and its copolymers, such as poly-(beta-hydroxybutyric-co-beta-hydroxyvaleric) acid [P(HB-co-HV)], are biodegradable polyesters with potential industrial applications.

Purpose of the Study:

• To investigate the microbial synthesis of P(HB-co-HV) copolymer by various bacterial strains.
• To optimize fermentation conditions for maximizing PHA yield and controlling copolymer composition.

Main Methods:

• Cultivation of bacterial strains including Alcaligenes latus and Alcaligenes eutrophus under different nutrient limitations (nitrogen, carbon-to-nitrogen ratio).
• Supplementation with propionic acid or pentanoic acid as co-substrates to induce copolymer formation.
• Fed-batch and chemostat culture techniques were employed to study PHA accumulation and composition.

Main Results:

• Several bacterial species accumulated P(HB-co-HV) when supplied with glucose/sucrose and propionic acid under nitrogen limitation.
• A. eutrophus produced up to 33% (wt/wt) PHB in chemostat culture, and 17 g/L of P(HB-co-HV) in fed-batch culture.
• A. latus achieved higher P(HB-co-HV) content, reaching 58% (wt/wt) in a two-stage chemostat, with HV content modulated by propionic acid concentration.

Conclusions:

• Bacterial strains can be engineered to produce P(HB-co-HV) copolymers with tunable compositions.
• Controlling carbon substrate feeding and nutrient limitation are key strategies for optimizing PHA production and properties.
• The study demonstrates the feasibility of producing P(HB-co-HV) for potential biotechnological applications.