SPECIFICITY OF THE PROTEIN SECRETORY APPARATUS - SECRETION OF THE HEAT-LABILE ENTEROTOXIN-B SUBUNIT PENTAMERS BY DIFFERENT SPECIES OF GRAM(-) BACTERIA

The B-subunit pentamer(s) (EtxBp) of Escherichia coli heat-labile ente rotoxin (LT) are secreted from Vibro io choleiae via the general secre tion pathway (GSP), but remain periplasmic in E. coli. In order to det ermine if other Gram bacteria were also able to secrete the ExtBp, the etxB gene, which encodes EtxB was introduced into different bacteria. Of the bacteria examined, most species of Vibrio and Aeromonas were a ble to secrete this protein through the outer membrane; other Gram(-) genera, including Erwinia, Klebsiella and Xanthomonas were not, even t hough they encode GSP genes homologous to those of V. cholerae. Thus, the ability to recognize the EtxBp as a secretable protein is confined to bacteria that were identified as being closely related to V. chole rae by examination of their 5S rRNA [MacDonell and Colwell, Syst. Appl . Microbiol. 6 (1985) 171-182].