S131: Cyanobacterial conversion of carbon dioxide to 2,3-butanediol

Cyanobacteria offer advantages to microbial fuel and chemical production, including use of non-arable land, high-efficiency photon harvesting, and direct production. Despite this, synthetic pathway construction in cyanobacteria is still nascent compared to model fermentative organisms. In this study we systematically developed the 2,3-butanediol (23BD) biosynthetic pathway in Synechococcus elongatus strain PCC 7942 as a model system to establish design methods for efficient exogenous chemical production in cyanobacteria. To adapt production to photosynthetic cells we matched reducing cofactors with the host, avoided oxygen sensitive enzymes, and optimized gene codons. We further applied irreversible enzymatic steps to create a driving force toward the target, and identified low toxicity of the product enabling high titers. By optimization of enzyme combinations production of 23BD from CO₂ reached 2.38 g/L, which is a significant increase for chemical production from exogenous pathways in cyanobacteria. We concurrently observed an increase in oxygen evolution by chlorophyll correlating to high carbon redirection away from metabolism, which may indicate possibilities for increases in photosynthetic efficiency overall. This work demonstrates that developing strong design methods can continue to increase chemical production in cyanobacteria.