INFLUENCE OF PHOSPHOLIPID-COMPOSITION ON EXCRETION OF BETA-LACTAMASE FROM A STRINGENT RELAXED ESCHERICHIA-COLI K-12 STRAIN PAIR/

In comparison to stringent (relA(+)) controlled Escherichia coli cells , relaxed (relA) controlled E. coli cells excreted more recombinant be ta-lactamase into the culture medium. The analysis of the composition of phospholipid fractions of the cells yielded increased levels of pho sphatidylserine in relaxed controlled cells. We added various phosphol ipid vesicles to growing cells in order to influence the excretion rat e via their incorporation in the membranes. The addition of vesicles o f phosphatidic acid, phosphatidylglycerol and phosphatidylserine reduc ed the excretion of beta-lactamase whereas vesicles of phosphatidyleth anolamine and phosphatidylchoIine decreased or increased the excretion of beta-lactamase in dependence on the individual fatty acid residues of the added phospholipids. The lower the degree of saturation of the added phospholipids the more permeable was the cell envelope for beta -lactamase.