Biosynthetic polyesters consisting of 2-hydroxyalkanoic acids: current challenges and unresolved questions

Area of Science:

• Biotechnology
• Polymer Science
• Microbial Engineering

Background:

• Bacterial polyhydroxyalkanoates (PHAs) are increasingly incorporating 2-hydroxyalkanoates (2HAs) as monomeric units.
• Key enzymes like PHA synthase and propionyl-CoA transferase are crucial for incorporating monomers such as lactate (LA), glycolate (GL), and 2-hydroxybutyrate (2HB).

Purpose of the Study:

• To explore the biosynthesis of novel PHAs containing 2HA monomers, focusing on lactate, glycolate, and 2-hydroxybutyrate.
• To investigate the properties of these new polymers and the potential for engineering PHA synthases for enhanced monomer incorporation.

Main Methods:

• Utilizing engineered microbes for the synthesis of PHAs with 2HA monomers.
• Engineering the class I PHA synthase from Ralstonia eutropha to incorporate lactate units.
• Analyzing the properties of synthesized polymers, including pliability and stretchiness.

Main Results:

• Successfully synthesized PHAs containing lactate (LA), glycolate (GL), and 2-hydroxybutyrate (2HB) monomers.
• LA-based polymers, such as P[LA-co-3-hydroxybutyrate (3HB)], exhibit pliability and stretchiness, unlike rigid poly(lactic acid) (PLA) and P(3HB).
• Enantiospecific PHA synthase enabled the production of isotactic (R)-2HB-based polymers, including P[(R)-2HB], from racemic 2HB precursors, yielding a pliable material.

Conclusions:

• Engineered microbes provide a versatile platform for producing novel PHAs with tunable properties by incorporating 2HA monomers.
• The development of an LA-polymerizing PHA synthase opens new avenues for creating advanced block copolymers.
• The synthesized 2HA-based polymers offer unique material characteristics, expanding the application range of biodegradable plastics.