Cyanobacteria offer advantages to microbial chemical production from CO2, including use of non-arable land, high-efficiency photon harvesting, and direct production. Despite this, biochemical production in cyanobacteria is still nascent compared to model fermentative organisms. In this study we systematically developed the 2,3-butanediol biosynthetic pathway in the cyanobacterium, Synechococcus elongatus PCC 7942 as a model system to establish design methods for efficient exogenous chemical production from cyanobacteria. 2,3-Butanediol is readily convertible to butadiene, butenes and methyl ethyl ketone, which in turn are used for the production of textiles, polymers, synthetic rubbers, plastics, fuel additives, and several different hydrocarbon fuels. 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 we achieved production with apparent limitation only by endogenous carbon flux to synthetic precursors. 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. Production of 2,3-butanediol from CO2 reached 2.38 g/L, which is a significant increase for chemical production from exogenous pathway in cyanobacteria.

Cyanobacterial conversion of carbon dioxide to 2,3-butanediol

247th National Meeting (2014)

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