Inhibition of protein secretion by cerulenin in Bacillus subtilis

Cerulenin at a concentration of 10 micrograms ml-1 only slightly inhibited growth of Bacillus subtilis YY88 while at 50 micrograms ml-1 it inhibited the growth rate by 20-35% in complex media, and by 50-60% in mineral medium containing a single carbon source. Cerulenin (50 micrograms ml-1) only partially prevented the secretion of alpha-amylase, proteases and levansucrase when added to bacteria growing in complex medium, but completely prevented the secretion of these enzymes in the mineral medium. Lower concentrations of cerulenin (10 micrograms ml-1) inhibited the secretion of the enzymes in the mineral medium by up to 40%. When the cells were incubated with L-[35S]-methionine (plus a complete amino acid mixture) in the presence of cerulenin (50 micrograms ml-1), protein secretion was lowered by 68%. Cerulenin inhibited translocation of membrane-bound forms of the secreted enzymes to 18% of the control value and the incorporation of radioactive methionine into membranes to 46%. These results suggest that the membrane-bound forms of secreted proteins play an important role in the secretion process in B. subtilis.