Rapid and efficient genetic transformation of the green microalga Chlorella vulgaris

Chlorella is a green unicellular alga that has a wide range of future biotechnical applications such as production of pharmaceuticals and biodiesel. Efficient genetic transformation of Chlorella vulgaris has been difficult due to technical limitations. In this study, an efficient and reliable transformation system of electroporation was established using two different reporter genes. First, C. vulgaris cell wall was digested with enzyme mixture for preparing protoplasts. The optimal transformation efficiency was 1.67 x 10(4) +/- 0.083 cfu mu g(-1) plasmid under the following conditions: 2 x 10(6) cells mL(-1) of growing culture; 655 V pulse voltage with 3.4 ms pulse width. After transformation, green and cyan fluorescence were observed from transgenic C. vulgaris harboring gfp (green fluorescent protein) gene of pCAMBIA1302 and cfp (cyan fluorescent protein) gene of pSK397, respectively, using laser confocal microscope. RT-PCR analysis as well as Southern blot confirmed the integration of reporter gene at the molecular level. This efficient transformation system of C. vulgaris would be valuable for the production of recombinant proteins in the future.