1-06: System biology and metagenomics applied to bioplastic production from hemicellulosic hydrolysate

Depending on their monomer composition, polyhydroxyalkanoates (PHA) can be either termoplastics or elastomeric materials. In the bacterial metabolism, PHA synthases are determinants to define PHA monomer composition. This research focuses in the: (i) improvement of PHA properties and (ii) utilization of inexpensive carbon sources. Considering the first issue, a PCR screening on a metagenomic library from Atlantic Rainforest's soil allowed the isolation of 100 clones harboring putative PHA-encoding genes, currently being sequenced. Using new PHA synthases we expect to be able to produce PHA with improved properties. Considering the second issue, a new soil isolated Burkholderia sp. F24 was capable to use xylose and remove organic inhibitors from hemicellulosic hydrolysates with simultaneous production of polyhydroxybutyrate (PHB). High cell density cultivation using hemicellulosic hydrolysate to produce PHB reached dry biomass of 25 g l^-1, containing 49.31% of PHB and 0.28 g l^-1 h^-1 of volumetric productivity. In silico simulations predicted that PHB yield from xylose could be improved from 0.25 (in vivo results) to 0.40 g g^-1 and PHA accumulation to 80% of CDW by increasing the NADPH availability in the system and avoiding catabolite repression. Therefore, we expressed (i) a modified CRP, independent of cAMP, to release catabolic repression and a (ii) transaldolase to increase the flux through the lower part of the Pentose Phosphate Pathway to produce an extra NADPH during the conversion of glucose-6P to glucono-1,5-lactone-6P, increasing growth rate, PHB accumulation and PHB yield in our strain.