Metabolic Engineering of Ralstonia Eutropha for the Biosynthesis of Polyhydroxyalkanoates from Sucrose

Sucrose is one of the most abundant and relatively inexpensive carbon sources extracted from sugarcane and sugar beet. To develop sucrose utilizing Ralstonia, which is polyhydroxyalkanoates (PHAs) producer, Ralstonia eutropha NCIMB11599 and R. eutropha 437-540 expressed Mannheimia succiniciproducens MBEL55E sacC gene that encodes β-fructofuranosidase. It was found that β-fructofuranosidase excreted into the culture medium could hydrolyze sucrose to glucose and fructose, which were efficiently used as carbon sources by recombinant R. eutropha strains. When R. eutropha NCIMB11599 expressing the sacC gene was cultured in nitrogen-free chemically defined medium containing 20 g/L of sucrose, a high P(3HB) content of 73.2 wt% could be obtained. In addition, R. eutropha 437-540 expressing the Pseudomonas sp. MBEL 6-19 phaC1437 gene and the Clostridium propionicum pct540 gene accumulated P(3HB-co-21.5mol%LA) to a polymer content of 19.5 wt% from sucrose by the expression of the sacC gene and the Escherichia coli ldhA gene. The engineered R. eutropha strains reported here will be useful for the production of polyhydroxyalkanoates from sucrose, one of the most abundant and relatively inexpensive carbon sources. [This work was supported by the Technology Development Program to Solve Climate Changes on Systems Metabolic Engineering for Biorefineries from the Ministry of Science, ICT and Future Planning (MSIP) through the National Research Foundation (NRF) of Korea (NRF-2012M1A2A2026556 and NRF-2012M1A2A2026557).]