THE ANTIBACTERIAL EFFECT OF ATTACINS FROM THE SILK MOTH HYALOPHORA-CECROPIA IS DIRECTED AGAINST THE OUTER-MEMBRANE OF ESCHERICHIA-COLI

The attacins are antibacterial proteins which accumulate in the hemolymph of the giant silk moth, H. cecropia, in response to a bacterial infection. The permeability barrier function of the outer membrane is affected shortly after addition of attacin to growing cultures of E. coli. Specifically, the penetration through the outer membrane of .beta.-lactam antibiotics, chicken egg white lysozyme and the detergent Triton X-100 was found to be facilitated. The sensitivity of E. coli to cecropin B, another antibacterial protein present in the hemolymph of H. cecropia, was also found to be increased after treatment with attacin. The results suggest that the target of the attacins in E. coli is the outer membrane. Other effects of the attacins which were observed are likely to be indirect consequences of the alteration in the properties of the outer membrane. These effects include changes in the cell shape, irregular patterns of cell division and lysis. The minimal concentration at which the attacins affected the growth of E. coli was 1 and 0.5 .mu.M for the neutral (pI [isoelectric point] 7) and basic (pI 9) attacins, respectively, which corresponds to < 2% of the concentration of the attacins in the hemolymph of infected pupae.