Microalgal Synthetic Biotechnology: From Genetic Models to Deployable Photosynthetic Chassis

Microalgae have long been considered promising platforms for producing biochemicals and supporting environmental applications. Realizing this potential will require turning microalgal species into predictable and reusable engineering platforms. However, it remains challenging to engineer such evolutionarily diverse, compartmentalized photosynthetic eukaryotes in a predictable way, because their behavior depends strongly on organelle organization, gene-expression context, and cultivation conditions. Here, we focus on 3 well-developed but functionally distinct chassis. Chlamydomonas reinhardtii provides the strongest genetic and cell-biological foundation among green microalgae; Phaeodactylum tricornutum serves as the main diatom system for genome engineering and systems-level pathway analysis; and Nannochloropsis spp., especially N. oceanica and N. gaditana, are more production-oriented and are particularly important for lipid engineering. We assess these chassis from the perspective of practical engineerability, including transformation and genome access, expression design, precise editing and regulatory control, and iterative design-build-test-learn workflows. We then discuss 4 representative trait areas: photosynthetic productivity and stress tolerance, storage lipids and omega-3 fatty acids, terpenoids and carotenoids, and pollutant removal. Despite substantial progress, the field is still limited by unstable transgene expression, weak portability of genetic parts, incomplete understanding of intracellular pathway organization, and poor agreement between laboratory phenotypes and process performance. Progress will require genetic design to be evaluated together with chassis physiology, cultivation performance, product recovery, and deployment-specific biosafety.