Direct Photosynthetic Production of Plastic Building Block Chemicals from CO₂

Hydroxy acids have attracted attention as building block chemicals due to their roles as precursors for the production of various pharmaceuticals, vitamins, antibiotics, and flavor compounds as well as monomers for biodegradable plastic polyesters. The current approach to hydroxy acid production relies on nonrenewable fossil resources such as petroleum for raw materials, raising issues such as the rising costs of starting materials and environmental incompatibility. Recently, synthetic biology approaches based on the rational design and reconstruction of new biological systems were implemented to produce chemicals from a variety of renewable substrates. In addition to research using heterotrophic organic carbon-dependent Escherichia coli or yeasts, photosynthetic microorganisms such as cyanobacteria possessing the ability to absorb solar radiation and fix carbon dioxide (CO₂) as a sole carbon source have been engineered into a new type of microbial cell factory to directly produce hydroxy acids from CO₂. In this chapter, recent progress regarding the direct photosynthetic production of three important hydroxy acids-3-hydroxypropionate (3-HP), 3-hydroxybutyrate (3-HB), and 3-hydroxyvalerate (3-HV)-from CO₂ in cyanobacteria is summarized and discussed.