Heterologous polyhydroxyalkanoate synthase expression enables poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)...

Area of Science:

• Biotechnology
• Polymer Science
• Microbial Engineering

Background:

• Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) is a biodegradable polymer with tunable mechanical properties.
• Current industrial PHBH production is limited by host systems and feedstocks.

Purpose of the Study:

• To develop Rhodobacter capsulatus as a novel host for PHBH production.
• To investigate the influence of substrate specificity and monomer supply on PHBH copolymer formation.

Main Methods:

• Engineered R. capsulatus SB1003 by integrating a broad-substrate PHA synthase.
• Cultivated engineered strains under anaerobic photoheterotrophic conditions.
• Supplemented cultures with various fatty acids (butyrate, hexanoate) to assess 3-hydroxyhexanoate (3HHx) incorporation.

Main Results:

• The engineered R. capsulatus strain accumulated PHBH up to 41.5% of cell dry weight with detectable 3HHx incorporation from butyrate.
• Attempts to increase 3HHx-CoA supply from butyrate via precursor modules yielded minor improvements.
• Cultivation on hexanoate resulted in PHBH with a high 3HHx content (32.4 mol%).

Conclusions:

• Demonstrated successful PHBH biosynthesis in R. capsulatus.
• Identified limited 3HHx-CoA supply as the primary bottleneck for copolymer production, not polymerization capacity.
• Established a foundation for optimizing R. capsulatus for flexible PHBH production from diverse feedstocks.