Summary Diderm bacteria have an outer membrane that provides defense against environmental factors including antibiotics. Understanding the process of outer membrane biogenesis is, therefore, of critical importance in order to envisage new treatments of these bacterial pathogens. Borrelia burgdorferi is the pathogen responsible for Lyme disease. Its outer membrane contains integral, beta-barrel proteins as well as swathes of externally exposed lipoproteins. Previous work has demonstrated that the beta-barrel assembly machine (BAM complex) in B. burgdorferi and other Spirochetes shares several similarities with the BAM complex in other bacterial lineages, such as the Proteobacteria that includes Escherichia coli. However, Iqbal et al. () have identified the inner membrane protein TamB as a subunit of the BAM complex in Spirochetes. This latest study highlights the modular nature of the BAM complex, and suggests that in some bacterial lineages the BAM complex and translocation and assembly module (the TAM) function as a single unit.