BIOSYNTHESIS OF POLY-3-HYDROXYBUTYRATE (PHB) IN THE TRANSGENIC GREEN ALGA CHLAMYDOMONAS REINHARDTII

A cell-wall deficient strain of Chlamydomonas reinhardtii P. A Dang. CC-849 was cotransformed with two expression vectors, p105B124 and pH105C124, containing phbB and phbC genes, respectively, from Ralstonia eutropha. The transformants were selected on Tris-acetate-phosphate media containing 10 μg · mL⁻¹ Zeomycin. Upon further screening, the transgenic algae were subcloned and maintained in culture. PCR analysis demonstrated that both phbB and phbC genes were successfully integrated into the algal nuclear genome. Poly-3-hydroxybutyrate (PHB) synthase activity in these transgenic algae ranged from 5.4 nmol · min⁻¹ · mg protein⁻¹ to 126 nmol · min⁻¹ · mg protein⁻¹. The amount of PHB in double transgenic algae was determined by gas chromatography-mass spectrometry (GC-MS) when comparing with PHB standard. In addition, PHB granules were observed in the cytoplasm of transgenic algal cells using TEM, which indicated that PHB was synthesized in transgenic C. reinhardtii. Hence, results clearly showed that producing PHB in C. reinhardtii was feasible. Further studies would focus on enhancing PHB production in the transgenic algae and targeting the chloroplast for PHB accumulation.