Influence of moderate temperatures on myristoyl-CoA metabolism and acyl-CoA thioesterase activity in the psychrophilic antarctic yeast Rhodotorula aurantiaca

The inability of psychrophilic microorganisms to grow at moderate temperatu res (>20 degreesC) presently represents an unresolved thermodynamic paradox . Here we report for the psychrophilic yeast Rhodotorula aurantiaca A19, is olated from Antarctic ice, that the inability to grow at temperatures close to 20 degreesC is associated with profound alterations in cell morphology and integrity. High performance liquid chromatography analysis of the intra cellular acyl-CoA esters revealed an abnormal accumulation of myristoyl-CoA (C14-CoA) in cells cultivated close to the nonpermissive temperature. Its concentration (500 muM) was found to be 28-fold higher than in cells cultiv ated at 0 degreesC, If one considers its ability to disrupt membrane bilaye rs and to inhibit many cellular enzymes and functions, intracellular myrist oyl-CoA accumulation in the psychrophile R, aurantiaca represents one of th e principal causes of growth arrest at moderate temperatures. Intracellular acyl-CoA concentrations are believed to be regulated by thioesterase activ ity. Thus in an attempt to explore the mechanism by which temperature disru pts myristoyl-CoA metabolism, we isolated and characterized a long chain ac yl-CoA thioesterase, The monomeric 80-kDa thioesterase from the psychrophil ic yeast shows a very strong specificity for myristoyl-CoA The affinity for substrate and the catalytic efficiency of the thioesterase are optimal bel ow 5 degreesC (temperatures habitually experienced by the strain) and drama tically decrease with increasing temperature. The loss of affinity for subs trate is related to the intracellular increase of myristoyl-CoA concentrati on. Our observations reveal one of the probable mechanisms by which tempera ture fixes the limit of growth for this psychrophilic yeast.