Abstract

Polyhydroxyalkanoates (PHA) has attracted industrial interest as bioplastics since the 1960's. PHA presenting different monomer compositions has been evaluated to replace petrochemical plastics in a number of applications. Copolymers of 3-hydroxybutyrate and medium-chain-length 3-hydroxyalkanoates (P3HB-co-3HAMCL) with molar fractions smaller than 20 mol% of 3HAMCL have attracted interest since they show similar properties to low density polyethylene. Polymers with larger fractions of 20 mol% 3HAMCL on the copolymer tends to be more elastic, resembling as PHA containing only medium–chain-length monomers produced mainly by bacteria belonging to Pseudomonas genus. Recently, we constructed a recombinant strain of Pseudomonas sp. harboring PHA biosynthesis genes from Aeromonas hydrophyla, with the ability to produce PHA containing high 3HHx fraction (> 20 mol%) besides small molar fraction of other 3HAMCL monomers from glucose. Therefore, it was proposed a genetic system for regulating the composition of the copolymer P3HB-co-3HAMCL based on the induction of genes responsible for the biosynthesis of 3HB monomers. To reach this aim, a plasmid containing a promoter PLAC and a repressor LacIq was used to control expression of genes phaA and phaB. As a preliminary test, the monomeric red fluorescent protein (mRFP1) reporter gene was placed into the plasmid instead of phaA and phaB genes. The inducible genetic system was functional in the host Pseudomonas sp. and it displayed a linear relation of induction with reporter protein expression up to 200 uM of IPTG, with 50% of total expression compared with a non-repressed control. For production assay of P3HB-co-3HAMCL the genes phaAB were replaced in mRFP1 along with the operon phaPC from Aeromonas hydrophyla. The effects of controlled expression of phaAB will be presented.