Genetic and biochemical characterization of a mutation (fatA) that allows trans unsaturated fatty acids to replace the essential cis unsaturated fatty acids of Escherichia coli

Abstract

Unsaturated fatty acid auxotrophs of Escherichia coli are able to use only unsaturated fatty acids of the cis configuration as the required growth supplement. A mutation in the fatA gene allows such auxotrophs to utilize unsaturated fatty acids with a trans double bond as well as fatty acids having a cis double bond. The fatA gene was mapped to min 69 near argG, and the allele studied (fatA1) was found to be dominant over the wild-type gene. fatA1 mutant strains grew at similar rates when supplemented with elaidate (trans-9-octadecenoate) or oleate (cis-9-octadecenoate). The fat+ strain, however, lysed when supplemented with the trans fatty acid. Physiological characterization of the fatA mutant strain was undertaken. The mutation appeared not to be involved with long-chain fatty acid transport. Introduction of lesions in known fatty acid transport genes abolished trans fatty acid utilization in the fatA mutant strain. Also, growth characteristics of the fat+ and the fatA1 mutant strains on elaidate as the sole carbon source were identical, which indicated comparables rate of fatty acid accumulation. The mutation appeared to be involved with recognition of the trans configuration after uptake into the cell. The levels of trans fatty acid incorporation into the phospholipids of the fat+ and the fatA strains differed considerably, with the mutant incorporating much higher levels. No significant accumulation of elaidate into nonphospholipid cellular components was observed. The fatA mutation did not appear to be involved with the cellular metabolic state, as cyclic AMP had no effect on the ability of the strains to utilize trans fatty acids.