A Burkholderia sacchari cell factory: production of poly-3-hydroxybutyrate, xylitol and xylonic acid from xylose-rich sugar mixtures

- Burkholderia sacchari able to produce P(3HB), xylitol and xylonic acid from xylose.
- Best feeding scheme for high P(3HB) productivity on glucose/xylose mixtures.
- High P(3HB) productivity and xylose consumption with glucose-rich sugar mixtures.
- High xylose concentrations in the medium induce xylitol production as by-product.
- Xylonic acid produced from xylose when a xylose-rich sugar mixture is used.

Efficient production of poly-3-hydroxybutyrate (P(3HB)) based on glucose-xylose mixtures simulating different types of lignocellulosic hydrolysate (LCH) was addressed using Burkholderia sacchari, a wild strain capable of metabolizing both sugars and producing P(3HB). Carbon catabolite repression was avoided by maintaining glucose concentration below 10 g/L. Xylose concentrations above 30 g/L were inhibitory for growth and production. In fed-batch cultivations, pulse size and feed addition rate were controlled in order to reach high productivities and efficient sugar consumptions. High xylose uptake and P(3HB) productivity were attained with glucose-rich mixtures (glucose/xylose ratio in the feed = 1.5 w/w) using high feeding rates, while with xylose-richer feeds (glucose/xylose = 0.8 w/w), a lower feeding rate is a robust strategy to avoid xylose build-up in the medium. Xylitol production was observed with xylose concentrations in the medium above 30-40 g/L. With sugar mixtures featuring even lower glucose/xylose ratios, i.e. xylose-richer feeds (glucose/xylose = 0.5), xylonic acid (a second byproduct) was produced. This is the first report of the ability of Burkholderia sacchari to produce both xylitol and xylonic acid.