Abstract: Projektet syftar till att utveckla stammar av bagerijäst som kan bilda butanol istället för etanol därför att butanol har fördelar som alternativt biobränsle jämfört med t.ex. etanol och därför att bagerijäst lämpar sig för storskaliga industriella processer. Arbetet bedrivs med molekylärbiologiska metoder. Projektet har hög grundforskningskvalitet och hög energirelevans.Abstract: The aim is to develop strains from baker´s yeast, Saccharomyces cerevisiae, which can produce butanol. Butanol is of interest as a motor fuel due to its higher energy content compared to ethanol. Yeast does not produce butanol, but lacks only one enzyme which would make that possible.This enzyme has been identified in strains of Lactobacilli and if this could be transferred to the yeast, a process similar to the ethanol production process could be developed. The work comprises various molecular biological methods to develop strains.Screening tests will be run, to isolate strains with desired properties. Various process concepts will be studied, batch and continuous cultivation, and also different process parametres, will be studied for their effect on butanol production. A problem is that butanol is toxic for microorganisms of interest, at concentrations of 2 %. A goal of the project is to isolate strains by evolutionary engineering, which have a higher tolerance limit.