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

We present evidence that biological properties of cell membranes are altere d in dnaA and seqA mutants of Escherichia coli relative to wild-type bacter ia. We found that bacteriophage lambda forms extremely large plaques on the dnaA seqA double mutants. On the single mutants, dnaA and seqA, the plaque s are also bigger than those formed on the wild-type host. However, no sign ificant differences in intracellular phage lambda development were observed between wild-type and mutant hosts, indicating that differences in burst s ize do not account for the observed differences in plaque size. On the othe r hand, more efficient release of the phage lytic proteins and/or higher se nsitivity of the cell membranes to these proteins may result in more effici ent cell lysis. We found that the efficiency of adsorption of bacteriophage lambda to the dnaA seqA mutant cells is decreased at 0 degrees C, but not at 30 degrees C, relative to the wild-type strain. A considerable increase in the permeability of membranes of the mutant cells for P-galactosidase is demonstrated. The dnaA and seqA mutants are more sensitive to ethanol tan organic solvent) than wild-type bacteria, and the seqA strain and the doubl e mutant dnaA seqA are very sensitive to deoxycholate (a detergent). We con clude that lesions in the genes dna 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.