TOLC AND DSBA ARE NEEDED FOR THE SECRETION OF STB, A HEAT-STABLE ENTEROTOXIN OF ESCHERICHIA-COLI

STB secretion-deficient mutants were isolated using the synthetic tran sposon Tn beta laM. Cultures were plated using a double-membrane syste m of cellulose acetate and nitrocellulose placed on Luria agar plates containing carbenicillin. The STB bound to the underlying nitrocellulo se membrane was detected with anti-STB antibodies. The altered genes o f two STB secretion-deficient mutants were identified by conjugation a nd complementation as tolC and dsbA. In cultures of well-characterized dsbA and tolC mutants, STB was absent from the culture supernatant Th e role of TolC and DsbA in the secretion of peptides is discussed.