S101: Engineering Synechococcus elongatus PCC 7942 to grow continuously in diurnal conditions

Synechococcus elongatus strain PCC 7942 strictly depends upon the generation of photosynthetically derived energy for growth and is incapable of biomass increase in the absence of light energy. In this work, we use synthetic biology approaches to probe and rewire photoautotrophic cyanobacterial metabolism for the ability to grow without light energy.  We determine that sugar transporter systems are the necessary genetic factors for continuous growth under diurnal (light/dark) conditions. Installing heterologous sugar transporters allowed the engineered strain to use saccharides such as glucose, xylose, and sucrose as both energy and carbon inputs.  This modified strain showed heterotrophic growth in the dark and a 2-fold growth rate increase in the presence of light. Cyanobacterial chemical production has gained increased attention. However, this obligate phototroph is incapable of product formation in the absence of light. Thus, converting an obligate photoautotroph to a heterotroph is desirable for more efficient, economical and controllable production systems.