Exchange of phospholipids between Escherichia coli cells and environment.

We studied the exchange of phospholipids between Escherichia coli K-12 cells and the suspension medium containing inactivated guinea-pig serum. In this medium, the release of 3H-labelled phospholipids was proportional both to the quantity of serum and to the temperature of incubation. No phospholipids were released when no guinea-pig serum was added to the medium, or the incubation temperature was 4 degrees C. The release of phospholipids into the medium was accompanied by an uptake of serum phospholipids by the cells, as demonstrated by incorporation of labelled phospholipids from the suspension medium. We conclude that an exchange occurs between the cellular phospholipids and those of the medium. Control tests with 3H-thymidine showed that cellular lysis was not involved.