Regulation of fatty acid chain length

All organisms regulate the fluidity of their membranes to maintain a membrane bilayer in a largely fluid state. As temperatures are lowered, membranes undergo a reversible change from a fluid (disordered) to a non-fluid (ordered) state. In E. coli, the temperature of the transition point depends on the fatty acid composition of the membrane phospholipids [12]. At lower temperatures, the amount of c/i-vaccenic acid is rapidly (within 30 s) increased due to the increased activity of FabF. Synthesis of mRNA and protein are not required. Mutants that lack FabF are unable to modulate their fatty acid composition in a temperature-dependent manner. Thus FabF, and not FabB, is involved in the thermal regulation of the fatty acid composition of the membranes. 

Other bacteria use different systems to regulate fluidity. For example, gram-positive bacteria alter the ratio of iso- to anteiso-branched-chain fatty acids in response to temperature [20]. However, the biochemical mechanisms that govern this universal response to environmental temperature are largely unknown in most bacterial species. 

---