ToIC and DsbA are needed for the secretion of ST_B, a heat-stable enterotoxin of Escherichia coli

ST_B secretion-deficient mutants were isolated using the synthetic transposon TnβlaM. Cultures were plated using a double-membrane system of cellulose acetate and nitrocellulose placed on Luria agar plates containing carbenicillin. The ST_B bound to the underlying nitrocellulose membrane was detected with anti-ST_B antibodies. The altered genes of two ST_B secretion-deficient mutants were identified by conjugation and complementation as tolC and dsbA. In cultures of well-characterized dsbA and tolC mutants, ST_B was absent from the culture supernatant. The role of TolC and DsbA in the secretion of peptides is discussed.