Chlorella species as hosts for genetic engineering and expression of heterologous proteins: Progress, challenge and perspective

The species of Chlorella represent a highly specialized group of green microalgae that can produce high levels of protein. Many Chlorella strains can grow rapidly and achieve high cell density under controlled conditions and are thus considered to be promising protein sources. Many advances in the genetic engineering of Chlorella have occurred in recent years, with significant developments in successful expression of heterologous proteins for various applications. Nevertheless, a lot of obstacles remain to be addressed, and a sophisticated and stable Chlorella expression system has yet to emerge. This review provides a brief summary of current knowledge on Chlorella and an overview of recent progress in the genetic engineering of Chlorella, and highlights the advances in the development of a genetic toolbox of Chlorella for heterologous protein expression. Research directions to further exploit the Chlorella expression system with respect to both challenges and perspectives are also discussed. This paper serves as a comprehensive literature review for the Chlorella community and will provide valuable insights into future exploration of Chlorella as a promising host for heterologous protein expression.