Strategies for high-level recombinant protein expression in transgenic microalgae: a review

Microalgae represent the 'best of both worlds', combining the high growth rate and ease of cultivation of microorganisms with the ability to perform post-transcriptional and post-translational modifications of plants. The development of economically viable microalgal expression systems is, however, hindered by low recombinant protein yields. Although there are still many obstacles to overcome before microalgae become standard expression systems, considerable progress has been made in recent years in regards to elucidating the causes for these low yields and in the development of strategies to improve them. Transgenes have successfully been expressed in both nuclear and chloroplast microalgal genomes, although at economically viable levels only in the latter. The present review describes recent progress in genetic manipulation of microalgae, outlines strategies to increase protein yields and presents some interesting avenues of research that remain to be explored.