Biosynthesis of Poly-beta-Hydroxyalkanoates from Pentoses by Pseudomonas pseudoflava

Area of Science:

• Microbiology
• Biotechnology
• Polymer Science

Background:

• Pseudomonas pseudoflava is a bacterium with potential for biopolymer production.
• Hemicellulosic biomass, particularly from poplar wood, is a sustainable resource for microbial fermentation.
• Poly-beta-hydroxyalkanoates (PHAs) are biodegradable polyesters with diverse applications.

Purpose of the Study:

• To investigate the capability of Pseudomonas pseudoflava to synthesize poly-beta-hydroxyalkanoates (PHAs) using pentoses derived from hemicellulose.
• To evaluate the influence of different carbon sources and fermentation conditions on PHA production and composition.
• To explore the production of PHA copolymers by P. pseudoflava.

Main Methods:

• Cultivation of Pseudomonas pseudoflava using hydrolysate from poplar wood hemicellulose.
• Batch fermentation experiments with varying hydrolysate concentrations and pure sugars (glucose, xylose, arabinose).
• Analysis of biomass composition, including poly-beta-hydroxybutyric acid (PHB) content, molecular weight, and copolymer composition upon propionic acid addition.

Main Results:

• P. pseudoflava successfully utilized poplar wood hydrolysate for growth, though high concentrations (>30%) were inhibitory.
• Significant accumulation of poly-beta-hydroxybutyric acid (PHB) was observed, with content ranging from 17% to 22% (wt/wt) of biomass dry weight on arabinose, glucose, and xylose.
• Specific growth rates varied significantly across substrates (0.58 h on glucose, 0.13 h on xylose, 0.10 h on arabinose).
• PHB molecular weights were high (up to 1,100,000 on glucose and xylose).
• Nitrogen limitation relaxation decreased absolute PHB amounts.
• Copolymer production of beta-hydroxybutyric and beta-hydroxyvaleric acids was achieved, reaching 45 mol% beta-hydroxyvaleric acid at 2 g/L propionic acid.

Conclusions:

• Pseudomonas pseudoflava demonstrates potential for producing PHB from hemicellulosic sugars.
• Optimizing fermentation conditions, including nitrogen availability, is crucial for maximizing PHB yield.
• The bacterium can be engineered to produce PHA copolymers with tunable properties by supplementing with fatty acid precursors.