Effect ofTemperature on theFattyAcid Composition ofThermus aquaticus

Thermus aquaticus contains fourmajorfatty acids, iso-C15 (28%), iso-C16 (9%), normal-C16 (13%), andiso-C17 (48%), whengrown at70C,as determined bygas chromatography andmass spectrometry. Smallamountsofiso-C12, normal-C12:1, iso-C,1, normal-C14, iso-C14, andnormal-C,,:, were alsodetected. A changein growth temperature (50to75C at5-Cintervals) affects a shift intheproportions of some ofthefatty acids. Theproportions ofthemonoenoic andbranched-C17 fatty acids decreased andtheproportions ofthehigher-melting iso-C16 andnormal-C16 fatty acids increased. Cells grown at75Ccontained 70%more total fatty acids than cells grown at50C.Thelargest increases, inabsolute amounts,were inthecontent ofiso-C16 andnormal-C,1 fatty acids, withonly a 1.6-fold increase inthemajoriso- C,1andiso-C1, fatty acids. There was a 2.5-fold decrease innormal-C,1, andat least a 24-fold decrease inanteiso-C17, whichispresentat50and55C butnotat higher temperatures. There was nodifference inproportion or amountoffatty acids between exponential andstationary-phase cells grown at70C.Whencells were grown on glutamate instead ofyeast-extract andtryptone at70C,thetotal fatty acid content remained constant, butthere was an increase intheproportions ofiso- C1,andnormal-C,1 fatty acids concomitant with a decrease intheproportions of theiso-C,5 andiso-C17 fatty acids. Themolecular mechanism ofthermophily has beenattributed to(i) thestability ofthelipids in themembrane, (ii) ahighrate ofbreakdown and synthesis ofthemacromolecules, and(iii) aphysi- cochemical difference between themacromole- cules ofthermophiles andmesophiles (17). Brock (3)hypothesized thattheintegrity ofthecell membrane maybethelimiting factor inthermal death, thussuggesting that themembrane compo- nentsofmesophiles andthermophiles should differ. Thefatty acidcomposition ofsomemeso- philes hasaprogressively higher melting point as thetemperature ofgrowth increases (14). Inthese organisms, theprogressively higher melting point corresponds todecreasing proportions ofmono- unsaturated fatty acids inthelipids. Recent workhasshownthatthermophiles con- tainlarger proportions ofbranched-chain satu- rated fatty acids thanmesophiles. Bacillus stear- othermophilus presumably grownathigh temper- ature contains 64%branched-chain fatty acids (7). Otherthermophilic sporeforming bacilli con- tainhigher proportions ofbranched-chain and straight-chain saturated fatty acidsandlower proportions ofunsaturated fatty acids thanmeso- philic strains (8). A comparison ofthefatty acid differences between thermophilic andmesophilic strains ofsporeforming bacilli indicated that higher temperatures ofgrowthcorrelate with higher proportions ofiso-branched-chain