The beta-barrel assembly module (BAM) and translocation and assembly module (TAM) are two multi-protein complexes embedded in the membrane of Gram-negative bacteria and are responsible for inserting and processing a whole host of proteins into the outer membrane. It is currently unknown what each component of these complexes is responsible for their function. To address this mutant strains of each component of the BAM and TAM have been systematically probed for their ability to process a wide range of substrates, deciphering the role of each component in outer-membrane biogenesis.