Effects of oleate starvation in a fatty acid auxotroph of Escherichia coli K-12

Abstract

The effects of oleate starvation on an oleate auxotroph of Escherichia coli K-12 were investigated. Following removal of oleate from the mutant growing in a minimal glycerol-peptone medium, the cells stopped making deoxyribonucleic acid, ribonucleic acid, protein, and phospholipids; they began to die exponentially and finally lysed. During oleate starvation in minimal medium minus peptone, inhibition of macromolecular syntheses and death occurred; however, lysis did not follow. When growth ceased, no further dying was observed. It is shown that none of the early effects (inhibition of macromolecular syntheses and death) can be due to leakiness of the cells, induction of a prophage or a colicin, or lack of energy sources. The cause of inhibition of macromolecular syntheses remained unknown. Since the rate of death was the same as the generation time under different conditions, it appears that death is due to the defective synthesis of some cellular structure (quite possibly, cytoplasmic membrane) during phospholipid deficiency. Lysis was found to require protein synthesis; electron microscopy revealed a peculiar type of "lysis from within"; i.e., the shape of the cells did not change but fragmentation of the inner layer of the cell envelope occurred. The murein was found to be unaltered. Most likely, lysis was a consequence of the cell's attempt to synthesize cytoplasmic membrane with altered phospholipid composition or during phospholipid deficiency. Several membrane functions (respiration, adenosine triphosphate formation, permeability) existing before oleate removal were not lost during starvation. Therefore, general damage to the membrane did not occur, and it could be that most, if not all, described effects were due to defective de novo membrane synthesis.