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 enterotoxin (LT) are secreted from Vibrio cholerae via the general secretion pathway (GSP), but remain periplasmic in E. coli. In order to determine 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 able to secrete this protein through the outer membrane; other Gram- genera, including Erwinia, Klebsiella and Xanthomonas were not, even though 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. cholerae by examination of their 5S rRNA [MacDonell and Colwell, Syst. Appl. Microbiol. 6 (1985) 171-182].