(725f) A Robust Light-Driven CO2 to Limonene Conversion By a Synthetic Microbial Consortium

A Robust
Light-Driven CO₂ to Limonene Conversion by a Synthetic Microbial
Consortium

Shrameeta Shinde, Kaya
Mernitz, and Xin Wang

Miami University,
Oxford OH

The
terpene family is very diverse with more than 50,000 unique chemical
structures. Terpenes are condensed from two C₅ precursor isomers, isopentenyl
pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). Limonene, a C₁₀
monoterpene, has been tested to use as a drop-in fuel additive for combustion
engines and as the kerosene substitute for aviation fuels. Terpene
biosynthesis has been explored in both heterotrophs and phototrophs. Photosynthesis
driven CO₂ conversion to terpenes is particularly attractive for
biofuel applications due to its low carbon footprint. However, terpene titer
achieved in phototrophs is far lower than that achieved in heterotrophs through
sugar conversion. We
hypothesize that the low terpene yield in phototrophs is due to the low driving
force determined by thermodynamics, i.e. the Gibbs free energy change (ΔG).
Thermodynamics
does not favor efficient photosynthetic CO₂ conversion, a situation
limited by CO₂ concentration and exacerbated by low photosynthesis
efficiency.
To bypass this limitation, we developed a synthetic photo-heterotrophic
microbial consortium to efficiently convert CO₂ into limonene. The photosynthetic
cyanobacteria were engineered to produce sugars, which then serve as the carbon
source for limonene production in the heterotrophic microbes through
co-culture fermentation. Implementing high-flux metabolic reactions in
phototrophs can create a strong carbon sink, and by constantly removing the
product, it can decrease ΔG and drive reactions toward products,
stimulating an enhanced photosynthesis and carbon fixation. The high sugar flux
from cyanobacteria can be captured by a natural microbial terpene producer to
synthesize limonene at high titer. We further investigated the consortium
strains through proteomics and metabolites analysis, and illustrate interesting
metabolic rewiring
that supports the robust CO₂ to limonene
conversion by the consortium. This study greatly expands our knowledge on
photosynthesis and carbon metabolism, and illustrates the merits of applying
microbial consortia for efficient chemical productions.