Engineering xylose metabolism for production of polyhydroxybutyrate in the non-model bacterium Burkholderia sacchari.

BACKGROUND: Despite its ability to grow and produce high-value molecules using renewable carbon sources, two main factors must be improved to use Burkholderia sacchari as a chassis for bioproduction at an industrial scale: first, the lack of molecular tools to engineer this organism and second, the inherently slow growth rate and poly-3-hydroxybutyrate [P(3HB)] production using xylose. In this work, we have addressed both factors. RESULTS: First, we adapted a set of BglBrick plasmids and showed tunable expression in B. sacchari. Finally, we assessed growth rate and P(3HB) production through overexpression of xylose transporters, catabolic or regulatory genes. Overexpression of xylR significantly improved growth rate (55.5% improvement), polymer yield (77.27% improvement), and resulted in 71% of cell dry weight as P(3HB). CONCLUSIONS: These values are unprecedented for P(3HB) accumulation using xylose as a sole carbon source and highlight the importance of precise expression control for improving utilization of hemicellulosic sugars in B. sacchari.

Carriers based on poly-3-hydroxyalkanoates containing nanomagnetite to trigger hormone release.

Poly-3-hydroxybutyrate (P(3HB)) and poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P(3HB-co-3HHx)) are biocompatible and bioabsorbable biopolymers produced by different bacteria with potential for drug delivery in thermo-responsive magnetic microcarriers. Microparticles of P(3HB) and P(3HB-co-3HHx), with 5.85% mol of 3HHx, produced by Burkholderia sacchari, containing nanomagnetite (nM) and lipophilic hormone were prepared by simple emulsion (oil/water) technique leading to progesterone (Pg) encapsulation efficiency higher than 70% and magnetite loads of 3.1 and 2.3% (w/w) for P(3HB)/nM/Pg and P(3HB-co-3HHx)/nM/Pg, respectively. These formulations were characterized by Infrared spectroscopy, X-ray diffraction, Thermal gravimetric analysis and Electron microscopy (TEM, SEM) techniques. The P(3HB)/nM/Pg and P(3HB-co-3HHx)/nM/Pg microparticles presented spherical geometry with wrinkled surfaces and average size between 2 and 40 µm for 90% of the microparticles. The release profiles of the P(3HB)/nM/Pg and P(3HB-co-3HHx)/nM/Pg formulations showed a hormone release trigger (6.9 and 11.1%, respectively) effect induced by oscillating external magnetic field (0.2 T), after 72 h. Progesterone release in non-magnetic tests with P(3HB-co-3HHx)/nM/Pg revealed a slight increment (5.6%) in relation to P(3HB)/nM/Pg. The experimental release of the P(3HB)/nM/Pg and P(3HB-co-3HHx)/nM/Pg samples presented a good agreement with Higuchi model. The 3HHx comonomer content improves the hormone release of the P(3HB-co-3HHx)/nM/Pg formulation with potential for application to synchronize the estrous cycle.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production from biodiesel by-product and propionic acid by mutant strains of Pandoraea sp.

Pandoraea sp. MA03 wild type strain was subjected to UV mutation to obtain mutants unable to grow on propionic acid (PA) but still able to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] from glycerol and PA at high 3HV yields. In shake flask experiments, mutant prp25 was selected from 52 mutants affected in the propionate metabolism exhibiting a conversion rate of PA into 3HV units of 0.78 g g-1 . The use of crude glycerol (CG) plus PA or valeric acid resulted in a copolymer with 3HV contents varying from 21.9 to 30 mol% and 22.2 to 36.7 mol%, respectively. Fed-batch fermentations were performed using CG and PA and reached a 3HV yield of 1.16 g g-1 , which is 86% of the maximum theoretical yield. Nitrogen limitation was a key parameter for polymer accumulation reaching up to 63.7% content and 18.1 mol% of 3HV. Henceforth, mutant prp25 is revealed as an additional alternative to minimize costs and support the P(3HB-co-3HV) production from biodiesel by-products. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1077-1084, 2017.