Aim Evaluation of the capability of Burkholderia sacchari to incorporate different monomers into polyhydroxyalkanoates (PHA). Methods and Results Thirty different carbon sources were evaluated as cosubstrates for B.sacchari growing on glucose with the intention to promote the incorporation of different monomers into the PHA produced by this species. With odd-numbered fatty acids, incorporation of the 3HV monomer was achieved, up to 65mol% in the case of valerate. With 4-hydroxybutyrate, incorporation of 4HB was obtained, representing 9 center dot 1mol%. With hexanoic acid, the production of P3HB-co-3HHx was achieved, containing up to 1 center dot 6mol% of 3HHx. The molar fraction of 3HHx was found to be dependent on the ratio of glucose to hexanoic acid supplied. Metabolic flux analysis revealed a high efficiency of B.sacchari in converting carbon sources into P3HB-co-3HHx. Nevertheless, hexanoic acid was only poorly converted to 3HHx. Conclusions Burkholderia sacchari is able to incorporate 3HV, 4HB and 3HHx in PHA containing mainly 3HB. The 3HHx content of P3HB-co-3HHx can be controlled by varying the glucose to hexanoic acid ratio. Burkholderia sacchari is highly efficient in converting carbon sources into PHA; however, only 2% of the hexanoic acid supplied could be converted to 3HHx. Significance and Impact of the Study This is the first report describing an approach to modulate the composition of P3HB-co-3HHx produced by bacteria using mixtures of carbohydrate and hexanoic acid as carbon source.