Heme staining and Tricine-polyacrylamide gel electrophoresis of outer membrane-enriched fractions prepared from wild-type, OmcF-deficient (omcF::kan), FC-adapted OmcF-deficient (FC-adapted omcF::kan), and complemented (omcF::kan/pRG5-omcF) strains. Outer membrane-enriched fractions were prepared from cultures grown in acetate-Fe(III) citrate or acetate-fumarate medium by Sarkosyl extraction (41). Outer membrane proteins (10 μg for panel A, 30 μg for panel B) were resolved on a 15% (A) or 7.5% (B) Tris-Tricine polyacrylamide gel and stained for heme. In order to resolve OmcB and OmcC (27), the gel shown in panel B was run until all proteins having molecular masses less than 30 kDa were off the gel.