Fatty acid synthesis in Escherichia coli

Abstract

Fatty acid formation by cells of a strain of E. coli has been studied in the exponential, post-exponential and stationary phases of growth. During the exponential phase of growth, the metabolic quotient (m[mu] moles of fatty-acid synthesized/mg dry wt. of cells/hr.) for each fatty-acid in the ex-tractable lipid was constant. The newly synthesized fatty-acid mixtures produced during this phase contained hexadecanoic-acid (41 percent), hexadeconoic-acid (31 percent), octadecenoid-acid (21 percent) and the C17-cyclopropane-acid, methylenehexadecanoic-acid (4 percent). As the proportion of newly snythesized material increased, changes in the fatty-acid composition of the cells during this period were towards this constant composition. Abrupt changes in fatty-acid synthesis occurred when exponential growth ceased. In media in which glycerol, or SO42- or Mg2+ , was growth-limiting there was a small accumulation of C17-cyclopropane acid in cells growing in the post-exponential phase of growth. Where either NH4+ or PO43- was growth-limiting and there were adequate supplies of glycerol, Mg2+ and SO42-, there was a marked accumulation of C17-cyclopropane acid and C19-cyclopropane acid appeared. Under appropriate conditions the metabolic quotient for C17-cyclopropane-acid increased up to sevenfold at the end of exponential growth. Simultaneously the metabolic quotients of the other acids fell. A mixture of glycerol, Mg2+ and SO42- stimulated cyclopropane-acid formation in resting cells.