Abstract: Bacteria that are not natural butanol producers were found to have increased tolerance to butanol when the saturated fatty acids content in bacterial cell membrane was increased. Methods for increasing the concentration of saturated fatty acids in the membranes of bacteria that are not natural butanol produces are described whereby tolerance of the bacterial cell to butanol is increased. Saturated fatty acids concentration in the bacterial cell membrane increased upon exogenously feeding saturated fatty acids to cells. Bacterial strains useful for production of butanol are described herein having modified unsaturated fatty acid biosynthetic pathway.