Engineered microbial biofuel production and recovery under supercritical carbon dioxide

Culture contamination, end-product toxicity, and energy efficient product recovery are long-standing bioprocess challenges. To solve these problems, we propose a high-pressure fermentation strategy, coupled with in situ extraction using the abundant and renewable solvent supercritical carbon dioxide (scCO₂), which is also known for its broad microbial lethality. Towards this goal, we report the domestication and engineering of a scCO₂-tolerant strain of Bacillus megaterium, previously isolated from formation waters from the McElmo Dome CO₂ field, to produce branched alcohols that have potential use as biofuels. After establishing induced-expression under scCO₂, isobutanol production from 2-ketoisovalerate is observed with greater than 40% yield with co-produced isopentanol. Finally, we present a process model to compare the energy required for our process to other in situ extraction methods, such as gas stripping, finding scCO₂ extraction to be potentially competitive, if not superior.