Class I Polyhydroxyalkanoate (PHA) Synthase Increased Polylactic Acid Production in Engineered Escherichia Coli

Area of Science:

• Biotechnology and Metabolic Engineering
• Polymer Science
• Microbial Fermentation

Background:

• Polylactic acid (PLA) is a biodegradable polyester with significant applications.
• Class II PHA synthases (PhaC1) are typically used for *de novo* PLA biosynthesis.
• Optimizing PLA production in engineered microorganisms is crucial for sustainable manufacturing.

Purpose of the Study:

• To evaluate a class I PHA synthase (PhaC) from *Chromobacterium* sp. USM2 for *de novo* PLA biosynthesis in *Escherichia coli*.
• To improve PLA production through morphological engineering by introducing the *sulA* gene.
• To assess the impact of fused propionyl-CoA transferase and lactate dehydrogenase A (fused Pct/LdhA) on PLA yields.

Main Methods:

• Genetic engineering of *Escherichia coli* to express class I PHA synthase (PhaC).
• Introduction of the *sulA* gene for morphological modifications in PLA-producing strains.
• Fermentation studies, including fed-batch cultivation, to quantify PLA production and characteristics.

Main Results:

• Class I PHA synthase (PhaC) demonstrated superior performance in PLA production compared to class II PHA synthase (PhaC1).
• Morphological engineering using the *sulA* gene significantly enhanced PLA production.
• Fused Pct/LdhA did not notably improve PLA yields.
• The engineered *E. coli* MS6 strain (PhaC and *sulA*) achieved a maximum PLA production of 955.0 mg/L with an average molecular weight of 21,000 Da.

Conclusions:

• Class I PHA synthase (PhaC) is a promising alternative for efficient *de novo* PLA biosynthesis.
• Morphological engineering via *sulA* is an effective strategy to boost PLA yields in engineered *E. coli*.
• The developed *E. coli* MS6 strain represents a significant advancement in microbial PLA production.