Important human pathogens such as Escherichia coli, Salmonella and Legionella, belong to the Gram-negative subclass of bacteria, the defining feature of which is an outer membrane that forms a protective barrier. The assembly of protein complexes in the outer membrane are essential for outer membrane biogenesis and survival of bacterial cells. In pathogenic strains, outer membrane protein complexes play additional roles in initiating productive infections. The majority of outer membrane proteins have a typical ß-barrel topology embedded in the membrane and are reliant on the ß-barrel assembly machinery (BAM) for correct and efficient assembly. In E.coli BAM is composed of five subunits, BamA, BamB, BamC, BamD and BamE. BamA is itself a ß-barrel protein containing a periplasmic domain thought to scaffold the remaining components. The four accessory lipoproteins are anchored to the outer membrane and like most known lipoproteins, assumed to face into the periplasm. Our recent analysis of the BAM component BamC, however disputes this current model and suggests the BAM complex spans the outer membrane displaying functional modules not only in the periplasmic space but also on the cell surface ¹. Work now continues to characterise the membrane-spanning region of BamC and to elucidate the mechanism by which it is transported to, and assembled on the cell surface.