Plasmid mediated alterations in composition and structure of envelopes of Escherichia coli B/r

Seven transmissible (Tra⁺), antibiotic resistance (r) plasmids, which confer sensitivity to the filamentous bacteriophage IKe on an Escherichia coli B/r strain harboring them, have been examined for the changes they evoke in the host cell membranes. The plasmids rR48and rR269, like rRM98 1], cause a significant reduction in the density of the outer membrane and the virtual elimination of its 36 500 dalton protein. These 2 properties do not appear to be altered when rR45, rR199 or rR205 are the resident plasmids. No changes in the inner membrane proteins are seen in any of these strains. In the case of the rR46-bearing strain, the density of the outer membrane is increased and the level of the 36 500 dalton protein is unaltered; in addition, several changes in both inner and outer membrane proteins are seen. Spontaneous IKe resistant mutants isolated from strains lacking the 36 500 dalton protein are either Tra⁺ or Tra^?. Since most of them also lack this protein, the latter is not important to the expression of inter-bacterial gene transfer and IKe sensitivity.On freeze fracture, strains lacking the 36 500 dalton protein cleave almost exclusively within the outer membrane. The plasmidless host and the remaining plasmid-bearing strains show a strong fracture plane within the cytoplasmic membrane. Despite the fact that most of the plasmid-bearing strains used are proficient in effecting interbacterial plasmid transfer, no morphological differences which can be correlated with this function have been observed between their etched cell surfaces and that of the plasmidless host.