Solvent Production by the Hyperthermophilic Archaeon Hyperthermus butylicus

Hyperthermus butylicus is a hyperthermophilic crenarchaeon capable of producing 1-butanol. In this study, it was determined that H. butylicus also produced key solvents, including acetone, isopropanol, and ethanol, using gas chromatography and/or high-performance liquid chromatography. These end-products resemble those produced by solventogenic Clostridium species. Solvent synthesis was growth-dependent and enhanced by supplementation with organic acids, such as acetate and butyrate. Sequence analysis could not show the presence of key homologs of known solvent-producing enzymes from other butanol-producing organisms, such as those of the acetone–butanol–ethanol pathway in Clostridium acetobutylicum. These results suggest that H. butylicus utilizes a metabolic route that is not fully elucidated. This work shows that H. butylicus is the first hyperthermophile that has been found to have the capability of ABE-like fermentation, thereby offering potential in biofuel research and thermophilic metabolic engineering.