The synthesis of mcl-polyhydroxyalkanoates (mcl-PHAs) by Pseudomonas sp. Gl01 using saponified waste palm oil (SWPO) as the sole carbon source was investigated. It was shown that the analyzed strain accumulated biopolymers during the growth phase. Up to 43% of mcl-PHAs at 17 h were produced, when Pseudomonas sp. Gl01 was grown for 48 h in a biofermentor containing 15 g/l of SWPO. The results clearly indicate that lower carbon source supplementation decreased mcl-PHAs production. Furthermore, the obtained results confirmed that nitrogen limitation is unnecessary for the stimulation of biopolymer synthesis. Additionally, in the present study the mcl-PHAs biosynthesis at the molecular level was also investigated. Using the RT real-time PCR technique, the expression of PHA synthase genes (phaC1 and phaC2) and PHA depolymerase gene (phaZ) was analyzed. The data suggest that the phaZ gene could be transcribed together with the phaC1 or phaC2 gene, which means that PHA synthesis and degradation followed simultaneously. Depending on the oily substrate concentration a wide range of repeat-unit components were observed. The purified polymers consisted of monomers ranging from C-6 to C-16. Moreover, a differential scanning calorimetric and gel permeation chromatography analysis confirmed that the extracted mcl-PHAs are elastomers with useful physical and chemical properties. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.