The elongation of exogenous fatty acids and the control of phospholipid acyl chain length in Micrococcus cryophilus.

The synthesis of fatty acids de novo from acetate and the elongation of exogenous satuated fatty acids (C12-C18) by the psychrophilic bacterium Micrococcus cryophilus (A.T.C.C. 15174) grown at 1 or 20 degrees C was investigated. M. cryophilus normally contains only C16 and C18 acyl chains in its phospholipids, and the C18/C16 ratio is altered by changes in growth temperature. The bacterium was shown to regulate strictly its phospholipid acyl chain length and to be capable of directly elongating myristate and palmitate, and possibly laurate, to a mixture of C16 and C18 acyl chains. Retroconversion of stearate into palmitate also occurred. Fatty acid elongation could be distinguished from fatty acid synthesis de novo by the greater sensitivity of fatty acid elongation to inhibition by NaAsO2 under conditions when the supply of ATP and reduced nicotinamide nucleotides was not limiting. It is suggested that phospholipid acyl chain length may be controlled by a membrane-bound elongase enzyme, which interconverts C16 and C18 fatty acids via a C14 intermediate; the activity of the enzyme could be regulated by membrane lipid fluidity.