Characterization of Escherichia coli mutants completely defective in synthesis of cyclopropane fatty acids.

The synthesis of cyclopropane fatty acids (CFA) in bacteria represents a biochemically and physiologically unique membrane modification whose importance for the cell remains unknown, despite extensive study of a Cfa- mutant of Escherichia coli and of the cloned cfa gene. Recently we reported the isolation of new Cfa- mutants (D. W. Grogan and J. E. Cronan, Jr., Mol. Gen. Genet. 196:367-372, 1984). Molecular-genetic and biochemical analysis indicated that these were null mutants of the E. coli cfa locus which were formed by inversions of a chromosomal segment. Isogenic Cfa+ and Cfa- strains were constructed from one such mutant and subjected to various stress conditions. In nearly all cases, both strains responded equally, but certain treatments, such as repeated freezing and thawing, favored the survival of Cfa+ strains over Cfa- strains. Though not essential, CFA thus appeared to play some beneficial role (or roles) in the bacterial cell.