Abstract

The composition of polyhydroxyalkanoates (PHA) determines their mechanical properties. This modulation allows obtaining PHA for different applications. Burkholderia sacchari, isolated from Brazilian soil, produces the copolymer poly-3-hydroxybutyrate-co-3-hydroxyhexanoate P(3HB-co-3HHx), a hybrid PHA that combines short-chain- (HA_SCL) and medium-chain-length (HA_MCL) monomers, thus showing promising properties for a wide range of applications. B. sacchari accumulated P(3HB-co-2mol%3HHx) from glucose and hexanoic acid. In this work we evaluated strategies to insert different amounts of 3HHx in the copolymer P(3HB-co-3HHx) produced by B. sacchari. In order to obtain P(3HB-co-3HHx) with larger 3HHx amount by B. sacchari was constructed a recombinant strain harboring phaPCJ operon genes from Aeromonas spp. Bioreactor cultivations with this strain were performed, fed by a solution containing glucose 140 g.l-1and hexanoic acid ranging from 0 to 45 g.l-1 in the accumulation phase. Copolymers containing 0, 6, 13, 15 and 19 mol% of 3HHx were obtained depending on the concentration of hexanoic acid supplied. The 3HHx yields from hexanoic acid were up to 0,5 g/g. The productivities showed by the cultivations of this recombinant strain were above 0,4 g/L.h, indicating it is an intersting strain to industrial processes. These copolymers were extracted and were prepared films to perform property analysis. The molecular weight average (Mn) obtained for these copolymer were 2x105 to 3x105. The glass transition temperature (Tg) was ranging from 4 to -3,2 °C, depending on the amount of 3HHx. According to the properties exhibited by these copolymers was suggested its application on flexible porous films or controlled release systems for medicine and dentistry.