“…To understand the mechanism of protein secretion across the outer membrane, xcp mutants have been isolated that are pleiotropically defective in the production of several extracellular proteins [6,17,18]. Some of the mutants obtained (mutations xcp-2, xcp-3, xcp-31, xcp-4 and xcp-41 through xcp-45) did not accumulate the exoproteins intracellularly [6]. These mutants, which are only affected in exoprotein synthesis on plates, but not in broth, probably contain a mutation in a regulatory gene, and will therefore not further be discussed here.…”