The hyperthermophilicarchaeon, Pyrococcus furiosus, growsoptimallynear100 °C byfermentingsugars
to acetate,carbondioxideandmolecularhydrogenasthemajorendproducts.Theorganismhasrecently
been exploitedtoproducebiofuelsusingatemperature-dependentmetabolicswitchusinggenesfrom
microorganisms thatgrownear70 °C. However,littleisknownaboutitsmetabolismatthelower
temperatures.Weshowherethat P.furiosus produces acetoin(3-hydroxybutanone)asamajorproductat
temperaturesbelow80 °C. Anoveltypeofacetolactatesynthase(ALS),whichisinvolvedinbranched-
chain aminoacidbiosynthesis,isresponsibleanddeletionofthe als gene abolishesacetoinproduction.
Accordingly,deletionof als in astrainof P.furiosus containing anovelpathwayforethanolproduction
significantly improvedtheyieldofethanol.Theseresultsalsodemonstratethat P.furiosus is apotential
platform forthebiologicalproductionofacetoinattemperaturesinthe70–80 °C range.