Cell envelope composition of G3.2 compared to WT EcNR1. Possible cell envelope adaptations in G3.2 were investigated by profiling cellular fatty acid composition and cell envelope proteins in G3.2 and the parent E. coli EcNR1 during growth at 0.5% (w/v) isobutanol. (A) Fatty acid composition of G3.2 and WT EcNR1. Relative proportions of cyclopropane, unsaturated, and saturated fatty acids were determined by GC-FID analysis. (B) SDS-PAGE profile of cell envelope proteins in G3.2 and WT EcNR1. Cell envelopes were isolated from 5 × 109 cells and analyzed by SDS-PAGE. For comparison, 20 μg total cellular proteins (TP) from each strain (WT and G3.2) were analyzed alongside the isolated cell envelopes (EP). As a reference, bands corresponding to outer membrane proteins OmpA and OmpC/OmpF are indicated with arrows. Experiment was repeated to verify results (not shown).