Isolation, Development, and Genomic Analysis of Bacillus megaterium SR7 for Growth and Metabolite Production Under Supercritical Carbon Dioxide

Supercritical carbon dioxide (scCO(2)) is an attractive substitute for conventional organic solvents due to its unique transport and thermodynamic properties, its renewability and labile nature, and its high solubility for compounds such as alcohols, ketones, and aldehydes. However, biological systems that use scCO(2) are mainly limited to in vitro processes due to its strong inhibition of cell viability and growth. To solve this problem, we used a bioprospecting approach to isolate a microbial strain with the natural ability to grow while exposed to scCO(2). Enrichment culture and serial passaging of deep subsurface fluids from the McElmo Dome scCO(2) reservoir in aqueous media under scCO(2) headspace enabled the isolation of spore-forming strain Bacillus megaterium SR7. Sequencing and analysis of the complete 5.51 Mbp genome and physiological characterization revealed the capacity for facultative anaerobic metabolism, including fermentative growth on a diverse range of organic substrates. Supplementation of growth medium with L-alanine for chemical induction of spore germination significantly improved growth frequencies and biomass accumulation under scCO(2) headspace. Detection of endogenous fermentative compounds in cultures grown under scCO(2) represents the first observation of bioproduct generation and accumulation under this condition. Culturing development and metabolic characterization of B. megaterium SR7 represent initial advancements in the effort toward enabling exploitation of scCO(2) as a sustainable solvent for in vivo bioprocessing.