Development of a stable genetic system for Chlorella vulgaris—A promising green alga for CO2 biomitigation

Abstract

Chlorella vulgaris has been proposed as a promising green alga for CO2 biomitigation due to its attractive traits of high growth rate, excellent CO2 fixation ability and broad industrial applications. Nevertheless, the genetic engineering of this alga is still in its infancy. In the present study, a stable and efficient transformation system was established for C. vulgaris CBS 15-2075, a robust strain with great potential for CO2 biomitigation. The antibiotic sensitivity spectrum of this organism was evaluated, and the nptII gene was selected as a dominant selectable marker for genetic transformation. The selectable marker, together with an enhanced green fluorescent protein (EGFP) gene, was delivered into C. vulgaris protoplasts by using a PEG-mediated method, giving a transformation efficiency of 356±30cfu per μg vector DNA. Molecular characterization and live-cell fluorescence microscopy demonstrated that the EGFP gene was stably integrated into C. vulgaris genome and expressed in the cytoplasm of transformed cells. Taken together, we for the first time established a stable and useful genetic toolkit for the industrially important microalga C. vulgaris, which will facilitate to a great extent the future rational genetic manipulation for strain improvement to increase CO2 fixation capacity and may as well provide valuable insights into other Chlorella species. Besides, the success in EGFP expression and live-cell fluorescence detection in C. vulgaris will be useful in molecular and cell biology for protein subcellular localization.