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 TnβIaM. 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 toIC and dsbA. In cultures of well‐characterized dsbA and toIC mutants, ST_B was absent from the culture supernatant. The role of ToIC and DsbA in the secretion of peptides is discussed.