Microalgae genome modification for the production of molecules of interest

Microalgae represent the first lung of our planet, capable of producing two-thirds of atmospheric oxygen. The second lung, made up of terrestrial forests, produces the remaining third. As the first link in the aquatic food chain and a key player in biogeochemical cycles, microalgae play a fundamental role in the biosphere. This article deals with microalgae, which we refer to as unicellular or undifferentiated multicellular photosynthetic eukaryotic microorganisms, excluding cyanobacteria, which are photosynthetic prokaryotic organisms.

Microalgae are a highly diverse group in terms of evolution (primary and/or secondary endosymbiosis), trophic mode (autotrophic and mixotrophic) and metabolism. They are veritable cellular factories capable of producing complex molecules such as lipids, proteins, polysaccharides, vitamins and pigments via photosynthesis, a redox reaction catalyzed by light energy to convert carbon dioxide into simple sugars and oxygen. Despite these exceptional physiological and metabolic properties, microalgae remain little exploited by industry, due to technological barriers that prevent them from being used reliably, efficiently and competitively. Increasing their productivity is therefore a major challenge. While process engineers optimize cultivation conditions to increase the production of a specific compound, geneticists propose modifying their genetic make-up to enable the production of natural and/or artificial compounds. Genetic engineering is an essential component of industrial biotechnology. Although microalgae were developed at a late stage compared with conventional industrial chassis (yeast, bacteria), the effort invested in developing engineering tools and methods in microalgae is now enabling them to compete with the latter.

In this article, we describe the evolution of microalgae genetic engineering since 1988, and its use to modify both quantitatively and qualitatively the content of natural compounds (lipids, carotenoids). We will also highlight their capacity to produce high value-added molecules (vaccines, hormones, terpenes, etc.).