Abstract
Poly(3-hydroxybutyrate) [P(3HB)] is the most representative polyhydroxyalkanoate (PHA), which is a storage polyester for prokaryotic cells. P(3HB)-producing recombinant Escherichia coli secretes diethylene glycol (DEG)-terminated 3HB oligomers (3HBO-DEG) through a PHA synthase-mediated chain transfer and alcoholysis reactions with externally added DEG. The purpose of this study was to optimize the culture conditions for the secretory production of 3HBO-DEG with jar fermenters. First, the effects of culture conditions, such as agitation speed, culture temperature, culture pH, and medium composition on 3HBO-DEG production, were investigated in a batch culture using 250-ml mini jar fermenters. Based on the best culture conditions, a fed-batch culture was conducted by feeding glucose to further increase the 3HBO-DEG titer. Consequently, the optimized culture conditions were reproduced using a 2-L jar fermenter. This study successfully demonstrates a high titer of 3HBO-DEG, up to 34.8 g/L, by optimizing the culture conditions, showing the feasibility of a new synthetic strategy for PHA-based materials by combining secretory oligomer production and subsequent chemical reaction.
Highlights
Polyhydroxyalkanoate (PHA) is a thermoplastic polyester that accumulates in microbial cells as an energy storage substance from renewable biomasses such as sugars and vegetable oils (Sudesh et al, 2000)
Our previous study showed a production of 4.32 g/L of 3HBODEG in a shake flask culture, with 50 g/L of diethylene glycol (DEG) added into the Lysogeny Broth (LB) culture medium (Hiroe et al, 2021)
The 3HB oligomers (3HBO)-DEG can be used as a macromonomer for the synthesis of PHA-based materials such as poly(3HBO-DEGurethane); the high production titer of 3HBO-DEG has not been achieved
Summary
Polyhydroxyalkanoate (PHA) is a thermoplastic polyester that accumulates in microbial cells as an energy storage substance from renewable biomasses such as sugars and vegetable oils (Sudesh et al, 2000). PHA, which is microbially produced, has excellent biodegradability in various environments, including marine environments (Suzuki et al, 2021), making it an attractive material for many scientists and engineers. The brittleness of P(3HB) can be improved by introducing second monomer units such as 3hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxy-4methylvalerate, and 4-hydroxybutyrate (Sudesh et al, 2000; Tanadchangsaeng et al, 2009). The presence of these second monomer units in the P(3HB) sequence prevents the crystallization of P(3HB), thereby resulting in increased flexibility of the material. Copolymerization can improve these mechanical properties, it does not contribute to reducing the production cost of PHA
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