NOVELTY - A butanol tolerant bacterial cell comprising engineered butanol biosynthetic pathway and increased concentration of membrane unsaturated trans fatty acids as compared with wild type cell, is new.    USE - The butanol tolerant bacterial cell is useful for producing isobutanol, 1-butanol or 2-butanol (all claimed) useful as industrial chemical, fuel additive, feedstock chemical in plastics industry, and food grade extractant in food and flavor industry.    ADVANTAGE - The concentration of unsaturated trans fatty acid, such as elaidic acid, vaccenic acid, and/or C16:1 trans fatty acid is increased as compared with wild type cell. The growth yield of the butanol tolerant bacterial cell is at least 1.6-3.5 times more with respect to 2.5% isobutanol, 1.6-3 times more with respect to 2.25% 1-butanol or 2.2-4 times more with respect to 4% 2-butanol, than the cell not containing increased concentration of membrane unsaturated trans fatty acids. The concentration of at least one membrane unsaturated trans fatty acid of the butanol tolerant bacterial cell is 44 times more than wild type cell.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) method for producing butanol tolerant bacterial cell; and    (2) method for producing isobutanol, involves (a) providing bacterial cell comprising engineered isobutanol biosynthetic pathway, feeding the bacterial cell with at least one trans fatty acid under conditions where the concentration of unsaturated trans fatty acids in the membrane of the cell are increased, and growing the bacterial cell under conditions where isobutanol is produced, or (b) providing bacterial cell comprising engineered isobutanol biosynthetic pathway and at least one gene encoding cis-trans isomerase, expressing the gene encoding fatty acid cis-trans isomerase, such that the concentration of unsaturated trans fatty acids in the membrane of the cell are increased, and growing the bacterial cell under condition where isobutanol is produced.