Altered biological properties of cell membranes in Escherichia coli dnaA and seqA mutants

We present evidence that biological properties of cell membranes are altered in dnaA and seqA mutants of Escherichia coli relative to wild-type bacteria. We found that bacteriophage λ forms extremely large plaques on the dnaA seqA double mutants. On the single mutants, dnaA and seqA, the plaques are also bigger than those formed on the wild-type host. However, no significant differences in intracellular phage λ development were observed between wild-type and mutant hosts, indicating that differences in burst size do not account for the observed differences in plaque size. On the other hand, more efficient release of the phage lytic proteins and/or higher sensitivity of the cell membranes to these proteins may result in more efficient cell lysis. We found that the efficiency of adsorption of bacteriophage λ to the dnaA seqA mutant cells is decreased at 0°?C , but not at 30°?C, relative to the wild-type strain. A considerable increase in the permeability of membranes of the mutant cells for β-galactosidase is demonstrated. The dnaA and seqA mutants are more sensitive to ethanol (an organic solvent) than wild-type bacteria, and the seqA strain and the double mutant dnaA seqA are very sensitive to deoxycholate (a detergent). We conclude that lesions in the genes dnaA and seqA result in alterations in cell membranes, such that the permeability and possibly also other properties of the membranes are significantly altered relative to wild-type bacteria.