Part of the outer membrane protein assembly complex (Bam), which is involved in assembly and insertion of beta-barrel proteins into the outer membrane. Constitutes, with BamD, the core component of the assembly machinery. Efficient substrate folding and insertion into the outer membrane requires all 5 subunits (PubMed:20378773, PubMed:21823654, PubMed:27686148). A lateral gate may open between the first and last strands of the BamA beta-barrel that allows substrate to insert into the outer membrane; comparison of the structures of complete and nearly complete Bam complexes show there is considerable movement of all 5 proteins (PubMed:27686148, PubMed:26900875, PubMed:26901871, PubMed:26744406). (Microbial infection) Acts as a receptor for CdiA-EC93, the contact-dependent growth inhibition (CDI) effector of E.coli strain EC93; antibodies against extracellular epitopes decrease CDI. Its role in CDI is independent of the other Bam complex components (PubMed:18761695). Is not the receptor for CdiA from E.coli strain 536 / UPEC, which does not have the same mode of toxicity as CdiA from strain EC93; the decreased expression of bamA101 in some experiments decreases the level of outer membrane proteins in general (PubMed:23469034, PubMed:23882017). Susceptibility to CdiA-EC93 is dependent on E.coli BamA; replacing BamA with the gene from S.typhimurium LT2, E.cloacae ATCC 13047 or D.dadantii 3937 renders cells resistant to CdiA-EC93. Cells with BamA from another bacteria no longer form CdiA-EC93-induced aggregates with EC93 cells. A chimera in which E.cloacae extracellular loops 6 and 7 are replaced with loops 6 and 7 from E.coli is susceptible to CdiA-EC93 and to CdiA-CT from strain 536 / UPEC (PubMed:23882017). Part of the Bam complex, which is composed of the outer membrane protein BamA, and four lipoproteins BamB, BamC, BamD and BamE. BamA interacts directly with BamB and the BamCDE subcomplex. The Bam complex has the shape of a hat, with the BamA beta-barrel crown in the outer membrane and the periplasmic brim formed by the BamA POTRA domains and the 4 lipoproteins (PubMed:27686148, PubMed:26900875, PubMed:26901871, PubMed:26744406). Contains 5 N-terminal periplasmic polypeptide transport-associated (POTRA) domains which interact with other subunits of the complex, may recruit substrates from the periplasm into the outer membrane and also act as a chaperone (PubMed:17702946, PubMed:18430136, PubMed:19081063, PubMed:21795783, PubMed:14559180). The C-terminal region forms a discontinuous 16-stranded beta-barrel transmembrane region. The central pore is ellipsoid, and probably closed by extracellular loop 6, perhaps with the aid of other loops (PubMed:24914988, PubMed:24619089). Deletion is lethal. Depletion results in the accumulation of incorrectly assembled outer membrane proteins, including TolC, OmpF, OmpC and OmpA (PubMed:15851030, PubMed:16102012). Decreased expression leads to decreased susceptibility to contact-dependent growth inhibition (CDI), and decreased expression of outer membrane proteins (including in this study LamB) as well as up-regulation of periplasmic protease DegP (PubMed:18761695, PubMed:23469034). Belongs to the BamA family.